Explosive Exercise

ACSM current comment


Explosive exercises, characterized by maximum or near maximum rates of force development, are effective for enhancing physical performance. In activities requiring high RFD, accelerations, or power outputs, explosive exercises are necessary for maximum development. Exercises can be selected in accordance with the concept of training specificity. As with other training methods, explosive exercises should be taught by experienced and knowledgeable instructors. When properly taught and supervised, explosive exercises are safe and likely to reduce the risk of injury during participation in sports and other activities that involve high RFD and acceleration.


Explosive exercise can be defined as movements in which the rate of force development (RFD) is maximum or near maximum for a given type of muscle action (e.g. isometric, concentric, eccentric). The peak RFD has a strong association with the ability to accelerate a mass. Explosive exercise may be performed isometrically or dynamically; however, dynamic movements can produce higher RFDs than isometric exercise. As the resistance used for dynamic movements decreases, the RFD increases resulting in an inverse relationship between peak force production and RFD. Thus, a continuum of explosive exercise can be conceptualized ranging from isometric movements and high force slow movements (very heavy weights) to very fast movements performed with relatively light weights. Depending upon the resistance used, a high RFD, high acceleration and power output can be achieved within the same movement. Explosive exercises in which all three parameters (RFD, acceleration and power) are at maximum or near maximum can be termed “speed strength” exercises and may be plyometric or ballistic in nature.

Explosive Exercise Training 

It is apparent in performing daily activities, and especially during many athletic activities, that a wide range of maximum strength, RFD, power and speed may be necessary for various movements. Additionally, gradations in these parameters can be required for the successful completion of various tasks.

There is little doubt that in both daily and athletic tasks maximum or near maximum efforts can be required, which depend upon high levels of strength, RFD and power. Considerable evidence suggests that periodic training with speed-strength exercises is necessary to maximally enhance RFD, power and speed. Explosive exercises, particularly speed strength exercises, are often used in the training of strength-power athletes but may be useful in training non-athletic populations as well. The efficacy of adaptations resulting from training with these exercises depends upon a variety of factors including the performance movement patterns, velocity requirements and the training state of the participants.

Untrained subjects respond to heavy weight training with a shift of the entire force-velocity curve upward and to the right. In strength-trained subjects, evidence indicates that high velocity or high power training is necessary for continued alterations in the high velocity portion of the force- velocity curve. Isometric training with a high RFD can increase the rate of force production and velocity of movement, while heavy weight training primarily increases measures of maximum strength. Additionally, high power explosive exercise training appears to increase a wide range of athletic performance variables to a greater extent than traditional heavy weight training, particularly if there is a reasonably high initial level of maximum strength. Both cross-sectional and longitudinal data suggest that in order to maximize strength, RFD, power and speed of movement, a combination of heavy and light explosive exercise provides superior results. Furthermore, evidence suggests that in order to maximize power output or speed of movement, the early portion of training should be devoted primarily to increasing maximum strength with the later portion of training being devoted primarily to power and speed training.

For example, during a 12-week training period designed to increase power and speed, the first five weeks would consist primarily of heavy explosive strength training. The next six weeks would consist of a combination of heavy and high power explosive exercise training, and the final week would be devoted to high power movements.

 Exercise selection 

Typical explosive exercises, including speed-strength exercises, consist of large muscle mass movements such as squats, derivatives of weightlifting movements (e.g. snatch and clean), weighted and unweighted vertical jumps and whole body ball throws. Smaller muscle mass exercises such as bench and incline pressing movements can be used as well as various types of upper body ball throws. Exercises can be selected in keeping with the principle of Specificity of Training, thus exercises can be used to stimulate movement, force, acceleration and velocity patterns of many sports and daily activities.

Injuries from strength training, including explosive exercises, are rare, with rates of occurrence and severity far lower than those in many sports such as soccer, football, basketball or gymnastics. Even though injury rates as a result of using explosive exercises are extremely low, adequate safety measures and quality instruction should always be enforced. Some evidence suggests that the injury potential associated with sports involving high RFD and accelerations can be reduced by requiring training with explosive exercises.

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Ankle Sprains and the Athlete

ACSM current comment


Ankle sprains are one of the most common injuries in the athlete. Accurate and rapid diagnosis, comprehensive treatment, and rehabilitation are critical in reducing the risk of re-injury or chronic disabling ankle pain. Prevention of injury should be a part of any training and exercise plan. The ultimate goal of any treatment program is to improve function without inhibiting the athlete’s performance


 Reports estimate that 25,000 Americans suffer from an ankle sprain each day. Ankle sprains account for almost half of all sports injuries and are a common reason why athletes take time off from activities. Accurate diagnosis is critical, as some studies suggest that 40 percent of ankle sprains are misdiagnosed or poorly treated leading to chronic ankle pain and disability. Self-education is therefore important in order to decrease the risk of this disabling complication.

What is an ankle sprain?

An ankle sprain is an injury to one or more of the ligaments in the ankle. These strong fibrous bands hold together the bones of the ankle and are prone to injury during strenuous movement and repetitive activity. There are two categories of ankle ligaments: those on the outer and those on the inner surfaces of the ankle. The most common sites of injury are in the outer – or “lateral” – ankle ligaments.

Common Causes

More than 80 percent of ankle sprains are a result of inversion, or inward rolling, of the ankle. This is commonly experienced in athletic activities that involve running, pivoting and jumping. While sudden, forceful movements are certainly the cause of many ankle sprains, low-grade repetitive trauma can also weaken and injure ankle ligaments. Risk factors for ankle sprains include previous ankle injury, impaired balance/postural control, type of sport played, position, and muscle strength/range-of-motion deficits. Excess body weight may also be a risk factor for males.

Evaluation and Diagnosis

Obtaining a thorough, detailed history of events is critical in the evaluation of ankle pain in order to lead to an accurate diagnosis. Immediate evaluation is important to determine if there are any other injuries such as a fracture. Common signs and symptoms of an ankle sprain include swelling, pain, instability and bruising. Numbness or severe weakness may suggest a related nerve injury. Examination of the ankle for evidence of instability and localizing pain is part of the initial assessment. Clinicians may often obtain x-rays or MRIs for further evaluation. A widely validated and sensitive rule of the thumb for assessing ankle sprains is known as the Ottawa Ankle Rules. These rules recommend imaging for possible fracture if there is pain on the side of the ankle with palpation and the patient is unable to walk four steps without pain. Ankle sprains are generally categorized into three grades:

Grade I : The most common type; these are associated with a mild degree of swelling and pain related to stretching of the ligament.

Grade II : More commonly seen in athletic injuries, these are associated with a moderate degree of swelling and pain and are related to an incomplete tear of the ligaments.

Grade III : The most severe of ankle sprains; these are associated with significant swelling and pain and are related to complete tear of the ligaments.

Initial Treatment and Prognosis

After an accurate diagnosis is obtained, treatment will vary depending on the severity of injury. Early and comprehensive treatment remains the best predictor of a good recovery. Initial treatment includes four common concepts referred to as R.I.C.E. (Rest, Ice, Compression, and Elevation). Relative rest or discontinuation of athletics is often necessary. Ice bags applied at 20-minute intervals three times per day for at least 72 hours post injury, along with compression and elevation, can help reduce swelling and pain. A thorough evaluation by a medical expert will help determine other possible treatments, including bracing, taping and anti-inflammatory medications.

Prognosis is directly related to the severity of injury. Immediate evaluation and treatment will often lead to an increased chance of complete recovery. Surgery is rarely necessary, as most ankle sprains will heal with conservative management.


A comprehensive rehabilitation program is a critical part in the treatment of ankle sprains. With the guidance of an experienced physical therapist or athletic trainer, stretching and strengthening of the ankle joint and calf muscles will quicken the recovery time and decrease the risk of re-injury. To maintain cardiorespiratory fitness during recovery,walking or jogging in a pool or cycling is recommended, as the weight on the ankle is decreased. Re-training the muscle sensation (called proprioception) and postural control (balance) should be a critical component of any rehabilitation program. Balance training, using ‘wobble boards’, is an excellent rehabilitation technique that helps strengthen and stabilize the ankle, reducing the risk of re-injury. Returning to activities usually varies from a few days to two months, depending on the severity of injury.

Prevention of Re-Injury

Prevention in athletics is an important matter to discuss with a skilled sports medicine practitioner. Properly applied external ankle supports (tape, semi-rigid, and rigid braces) and balance board exercise training can reduce the risk of ankle re-injury by more than 50%. These prevention strategies are especially effective for those with a history of a previous ankle injury. External ankle supports do not adversely affect athletic performance. Semi-rigid and rigid ankle supports are most effective, widely available, and cost less than athletic tape.

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Nutrition and Athletic Performance

Joint Position Statement: American Dietetic Association, Dietitians of Canada, and the American College of Sports Medicine


It is the position of the American Dietetic Association, Dietitians of Canada, and the American College of Sports Medicine that physical activity, athletic performance, and recovery from exercise are enhanced by optimal nutrition. These organizations recommend appropriate selection of foods and fluids, timing of intake, and supplement choices for optimal health and exercise performance.

This updated position paper couples a rigorous, systematic, evidence-based analysis of nutrition and performance-specific literature with current scientific data related to energy needs, assessment of body composition, strategies for weight change, nutrient and fluid needs, special nutrient needs during training and competition, the use of supplements and ergogenic aids, nutrition recommendations for vegetarian athletes, and the roles and responsibilities of the sports dietitian.

Energy and macronutrient needs, especially carbohydrate and protein, must be met during times of high physical activity to maintain body weight, replenish glycogen stores, and provide adequate protein to build and repair tissue. Fat intake should be sufficient to provide the essential fatty acids and fat-soluble vitamins and to contribute energy for weight maintenance. Although exercise performance can be affected by body weight and composition, these physical measures should not be a criterion for sports performance and daily weigh-ins are discouraged.

Adequate food and fluid should be consumed before, during, and after exercise to help maintain blood glucose concentration during exercise,maximize exercise performance, and improve recovery time. Athletes should be well hydrated before exercise and drink enough fluid during and after exercise to balance fluid losses. Sports beverages containing carbohydrates and electrolytes may be consumed before, during, and after exercise to help maintain blood glucose concentration, provide fuel for muscles, and decrease risk of dehydration and hyponatremia.

Vitamin and mineral supplements are not needed if adequate energy to maintain body weight is consumed from a variety of foods. However, athletes who restrict energy intake, use severe weight-loss practices, eliminate one or more food groups from their diet, or consume unbalanced diets with low micronutrient density may require supplements. Because regulations specific to nutritional ergogenic aids are poorly enforced, they should be used with caution and only after careful product evaluation for safety, efficacy, potency, and legality.

A qualified sports dietitian and, in particular, the Board Certified Specialist in Sports Dietetics in the United States, should provide individualized nutrition direction and advice after a comprehensive nutrition assessment.

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Alcohol and Athletic Performance

ACSM current comment

The effects of alcohol can depend on the amount consumed, the environmental context, and on the individual. Daily consumption of up to four drinks may have a protective effect on the cardiovascular system. Nonetheless, people most commonly drink for alcohol’s anxiolytic (stress-reducing) property. Conversely, alcohol has a wide spectrum of negative effects, from societal to physiological, accounting for approximately 100,000 deaths yearly in the United States. From a physiological perspective, two situations draw special attention for the fitness-oriented individual who consumes alcohol. Acutely, alcohol can cause negative effects on motor skills and physical performance. Chronically, alcohol abuse may eventually impede physical performance; individuals diagnosed with alcohol dependence have displayed varying degrees of muscle damage and weakness. Furthermore, alcohol abuse is at least as prevalent in the athletic community as it is in the general population; the vast majority of athletes have begun drinking by the end of high school.


Alcohol use by athletes often starts at the junior high school level and can start even earlier. Among high school students, male athletes are more likely to not only use alcohol regularly but also to abuse alcohol. This relationship does not seem to exist at the college level. Nonetheless, alcohol consumption is high enough for alcohol to have been named the most abused drug in collegiate sport by the NCAA and in professional and Olympic sports by the NFL, NBA, and USOC.


Each gram of alcohol (ethanol) provides seven kilocalories compared to nine for fat and four each for carbohydrate and protein. Other nutrients may be present, depending on the type of beverage. Beer, for example, has been seen as a good source of many nutrients and has sometimes been used in preparation for endurance events or to replenish nutrients following competition. Actually, orange juice supplies four times the potassium plus almost three times the carbohydrates, and it would take 11 beers, for example, to obtain the B-vitamin recommended daily allowance (RDA).


Motor Performance – Low amounts of alcohol (0.02-0.05g/dL) can result in decreased hand tremors, improved balance and throwing accuracy, and a clearer release in archery, but in slower reaction time and decreased eye-hand coordination. A moderate (0.06-0.10 g/dL) amount of alcohol negatively affects such skills.

Strength/Power and Short-term Performances – The effect of alcohol, in low to moderate doses, is equivocal. It can have a deleterious effect on grip strength, jump height, 200- and 400-meter run performance, and can result in faster fatigue during high-intensity exercise. Conversely, alcohol has been shown to lack an effect on strength in various muscle groups, on muscular endurance, and on 100-meter run time.

Aerobic Performance – Low or moderate amounts of alcohol can impair 800- and 1500-meter run times. Because of its diuretic property, it can also result in dehydration, being especially detrimental in both performance and health during prolonged exercise in hot environments.


Any lingering effect of alcohol would especially hinder physical conditioning progress. According to current research, the effect during a hangover seems to be undecided, with no effect on several performance variables, but a decline in total work output during high-intensity cycling. Furthermore, handgrip muscular endurance has been shown to suffer a delayed decline on the second morning following intoxication.


Chronic alcohol abuse may be detrimental to athletic performance secondarily to many of the sequelae that can develop. Alcohol affects the body’s every system, linking it to several pathologies, including liver cirrhosis, ulcers, heart disease, diabetes, myopathy, bone disorders, and mental disorders. The following implications may especially interest the athletic individual. Alcohol can result in nutritional deficiencies from alterations in nutrient intake, digestion, absorption, metabolism, physiological effects, turnover, and excretion of nutrients. Myopathy (muscle damage, wasting, and weakness) can occur in various muscles, including the heart, often compounded by alcohol-caused neuropathies. Also, the hormonal environment can change, making it less conducive to increasing muscle mass and strength.


There are various methods to screen for alcohol abuse. Standardized questionnaires are available, but taking a more subtle approach by adding questions in medical history forms may be more effective. A team physician may also look for certain signs in the athlete’s appearance, but this has limited usefulness; it is good only for extreme cases of alcoholism. Athletes should be informed of all of alcohol’s detrimental aspects. Team rules and guidelines such as the following can be used:

* Pre-event: Avoid alcohol beyond low-amount social drinking for 48 hours.

* Post-exercise: Rehydrate first and consume food to retard any alcohol absorption.

To address any underlying causes of alcohol abuse, professional counseling should be available to athletes either directly or by referring athletes to community resources.

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Eating Disorders

ACSM current comment

Many student-athletes face a difficult paradox in their training regimes. They are encouraged to eat to provide the necessary energy sources for performance, yet they often face self- or team-imposed weight restrictions. Emphasis on low body weight or low body fat may benefit performance only if the guidelines are realistic, the calorie intake is reasonable, and the diet is balanced. The use of extreme weight-control measures can jeopardize the health of the student-athlete and possibly trigger behaviors associated with defined eating disorders.

National Collegiate Athletic Association (NCAA) studies show that at least 40 percent of member institutions reported at least one case of anorexia or bulimia in their athletic programs. Although these eating disorders are much more prevalent in women (approximately 90 percent of the reports were in women’s sports), eating disorders also occur in men.

Eating disorders are often an expression of underlying emotional distress that may develop long before the individual becomes involved in athletics. It has been suggested that stress, whether it be from participating in athletics, striving for academic success, or pursuing social relationships, may trigger psychological problems, such as eating disorders, in susceptible individuals. Eating disorders can be triggered in such individuals by a single event or by comments from a person important to the individual. In athletics, such triggering mechanisms may include offhand remarks about appearance or constant badgering about an athlete’s body weight, body composition or body type.

Eating disorders often experienced by student-athletes and their warning signs include:

Anorexia Nervosa - Self-imposed starvation in an obsessive effort to lose weight and to become thin. Warning signs - Drastic loss in weight, a preoccupation with food, calories and weight, wearing baggy or layered clothing, relentless, excessive exercise, mood swings, and avoiding food-related social activities.

Bulimia - Recurring binge eating usually followed by some method of purging such as vomiting, diuretic or laxative abuse, or excessive exercise. Warning signs - Excessive concern about weight, bathroom visits after meals, depressive moods, strict dieting followed by eating binges, and increasing criticism of one’s body.

Bulimarexia - Anorexia nervosa with practice of one or more bulimic behaviors.

It is important to note that the presence of one or two of these warning signs does not necessarily indicate the presence of an eating disorder. Definitive diagnosis should be done by appropriate professionals.

Anorexia and bulimia lead to semi-starvation and dehydration, which can result in loss of muscular strength and endurance, decreased aerobic and anaerobic power, loss of coordination, impaired judgment and other complications that decrease performance and impair health. These symptoms may be readily apparent or they may not be evident for an extended period of time. Many student athletes have performed successfully while experiencing an eating disorder. Therefore, diagnosis of this problem should not be based primarily on a decrease in athletic performance.

Coaches, athletic trainers and supervising physicians must be watchful for student-athletes who may be prone to eating disorders, particularly in sports in which appearance or body weight is a factor in performance.

Fotografía de Pablo Salto-Weis

Fotografía de Pablo Salto-Weis

Decisions regarding weight loss should be based on the following recommendations to reduce the potential of an eating disorder:

1. Weight loss should be agreed upon by both the coach and the athlete with appropriate medical and nutrition personnel;

2. A responsible and realistic plan should be developed by all individuals involved, and

3. Weight loss plans should be developed on an individual basis.

If a problem develops, thorough medical evaluation of the athlete suspected of an eating disorder is imperative. Once confirmed, behavior modification should emanate from professional guidance through nutritional, psychological and/or psychiatric counseling. Because eating disorders are a growing problem with serious health consequences, the establishment of professionally guided support groups, access to personal counseling and an assistance hotline should be considered on every campus.

Education about eating disorders is a good preventive measure. In 1989, the athletics department at each member institution received the NCAA project “Nutrition and Eating Disorders in College Athletics.” These materials, which included videotapes and written supplements, should be reviewed by athletic administrators, coaches, medical personnel and athletes. In addition, in 1992, the American College of Sports Medicine began development of informational materials on the female athlete triad: disordered eating, amenorrhea, and osteoporosis. These materials also will be valuable resources for NCAA institutions, and can be requested by sending a self-addressed, stamped business size envelope to ACSM, c/o Triad, P.O. Box 1440, Indianapolis, IN 46206-1440.

Written by the National Collegiate Athletic Association and modified by the American College of Sports Medicine.

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Exercise During Pregnancy

ACSM current comment  -  

Exercise and physical fitness have dramatically gained in popularity over the past several years, and have assumed important roles in the lives of many women. Physical activity and reproduction are normal parts of life, and for normal healthy women, combining regular exercise and pregnancy appears to benefit both mother and baby in many ways. Thus, a healthy woman with a normal pregnancy may either continue her regular exercise regimen, or begin a new exercise program. The American College of Obstetrics and Gynecology (ACOG), as well as the American Society for Obstetrics and Gynecology (ASOG), recommends that normally healthy pregnant women may continue an already-established exercise regimen.

Pregnancy is a normal physiological state characterized by growth of both mother and fetus. From conception onward, the fetus develops into a baby, and the mother experiences both physical and psychological growth. All mothers want the best possible health for themselves and their babies, but some women and physicians are concerned that regular maternal physical activity during pregnancy may cause miscarriage, premature delivery, poor fetal growth, or musculoskeletal injury. For normal pregnancies, these concerns have not been substantiated. Indeed, participation in regular weight-bearing exercise has been shown to improve maternal fitness, restrict weight gain without compromising fetal growth, and hasten postpartum recovery. In addition, the psychological benefits of exercise are undeniable, and should be nurtured by all who care for pregnant women. During the first trimester, major physiological changes are taking place, even though maternal body changes are few. During low-level exercise, blood pressure and pulse responses are not dramatically different from those in the non-pregnant woman, but fatigue may be noticed earlier during exercise. As early pregnancy progresses, blood volume expands and the uterus continues to enlarge. Weight gain is usually small but can range from zero to ten pounds. During this time, the fetus is undergoing its most important growth, including development of organs and limbs. For this reason, a proper balance of nutrition, hydration, exercise and rest assume great importance. It is important for the pregnant woman to avoid large increases in her body temperature during exercise. Fortunately, adequate hydration, regular exercise, and pregnancy all improve a woman’s capacity to dissipate heat. The individual effects of these on heat dissipation appear to complement one another when combined. Thus, well hydrated, fit pregnant women regulate their core body temperatures more efficiently than sedentary people, and undergo less temperature variation during exercise. Loose fitting clothing and a cool environment are also important in protecting against heat stress. Other environmental conditions to consider are very high and very low air pressure. Exposure to the decreased oxygen of high altitudes, as well as the high pressures experienced during deep sea diving, should be avoided during pregnancy.

The second and third trimesters are accompanied by dramatic changes in a woman’s body. Normal weight gain ranges between 22 and 35 pounds and is centered around the abdomen and pelvis, which alters both posture and the center of gravity. During this time, exercises requiring balance and agility may become more difficult due to the change in the pregnant woman’s weight distribution. The use of properly adjusted exercise equipment, a smooth floor surface, and/or aquatic exercises are extremely helpful. The extra caloric demands of pregnancy are extremely variable; no fixed equation accurately estimates the amount of increased caloric need. The best measure of sufficient caloric intake is adequate weight gain. Small, frequent meals and regular fluid intake throughout the day are most desirable in maintaining a steady flow of nutrients while minimizing the discomfort of exercising on a full stomach, and avoiding dehydration and low blood sugar. Pregnant, sedentary women commonly require approximately 3,000 calories per day during the second and third trimesters to ensure adequate stores of nutrients. A physically active expectant mother would therefore have a higher caloric need, in order to compensate for calories burned off during strenuous exercise.

Sports Medicine provides the following recommendations:

Safety: As changes in weight distribution occur, balance and coordination may be affected. Exercise programs should be modified if they pose a significant risk of abdominal injury or fatigue as opposed to relaxation and an enhanced sense of well being. Until more information is available, exercising in the supine or prone positions should be avoided after the first trimester.

Environment: Temperature regulation is highly dependent on hydration and environmental conditions. Exercising pregnant women should ensure adequate fluid intake before, during and after exercise, wear loose-fitting clothing, and avoid high heat and humidity to protect against heat stress, especially during the first trimester.

Growth and Development: The pregnant woman should monitor her level of exercise and adjust her dietary intake to ensure proper weight gain. If pregnancy is not progressing normally or if vaginal bleeding, membrane rupture, persistent pain or chronic fatigue are noted, exercise should be stopped until a medical evaluation has been completed. Also, if regular contractions occur more than 30 minutes after exercise, medical evaluation should be sought. This may signify pre-term labor.

Mode: Weight-bearing and non-weight-bearing exercise are thought to be safe during pregnancy. Improved maternal fitness is a well-known benefit of non-weight-bearing exercise such as swimming and cycling. Weightbearing exercises are similarly beneficial as long as they are comfortable. Swimming and stationary cycling are excellent non-weight-bearing exercises, and may be recommended. Walking, jogging and low-impact aerobics programs are good choices when weight-bearing exercise is to be considered.

Heavy weightlifting, or similar activities that require straining, are to be discouraged. Bicycle riding, especially during the second and third trimesters, should be avoided because of changes in balance and the risk of falling. Exposure to the extremes of air pressure, such as in SCUBA diving and high altitude exercise in non-acclimatized women, should be avoided.

Intensity: Pregnancy is probably not a time for serious competition. For women who are continuing their regular exercise regimen during pregnancy, exercise intensity should not exceed pre-pregnancy levels. The intensity of exercise should be regulated by how hard a woman believes she is working. Moderate to hard is quite safe for a woman who is accustomed to this level of exercise.

Exercise: A healthy woman with a normal pregnancy may either continue her regular exercise regimen or begin a new exercise program during pregnancy. For your particular exercise prescription and its duration, check with your physician.

Written for the American College of Sports Medicine by Raul Artal, M.D., James F. Clapp, III, M.D., and Daniel V. Vigil, M.D., FACSM

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Strenght trainning for bones, muscle and hormones


ACSM current comment

One of the hallmark features of aging is loss: loss of bone strength, muscle mass and strength and hormone production. Although the debate continues as to the cause of this loss, one thing is certain: the inclusion of regular strength training sessions will play an important role delaying and reducing age- or inactivity-associated loss experience.

Bone Health 

Weak bones, osteopenia (low bone mass that precedes osteoporosis), porous bone or brittle bones are all terms used to characterize the condition known as osteoporosis. It is important to understand that osteoporosis is not a disease in the clinical sense, but a condition. Osteoporosis typically begins with an unnoticed decrease in bone mass that leads to structural deterioration of bone tissue and an increased susceptibility to fractures of the hip, spine and wrist. In fact, any bone can become susceptible to change in strength, particularly with age.

Until the age of about 30 to 35 years, our bones are in a constant state of building. Bone strength, however, can be affected by such things as heredity, diet, sex hormones, physical activity, lifestyle choices, and the use of certain medications. Osteoporotic symptoms occur earlier and last longer in women (40-65 years) than men (from 65 years). Osteoporosis is less common in men than in women for several reasons. Men have larger skeletons, their bone loss starts later in life and progresses more slowly, and they do not experience the rapid bone loss that affects women when their estrogen production drops as a result of menopause. Despite these differences, men can be at high risk for this condition.

Osteoporosis is prevalent in America. Eight million women and two million men experience osteoporosis. Eighteen million others are at risk with low bone mass, and 1.5 million fractures occur annually because of osteoporosis. The cost of osteoporosis to Americans is increasing; according to the National Osteoporosis Foundation of America, more than 38 million dollars are spent daily on osteoporotic and associated fractures.

Muscle Health 

Sarcopenia, a loss of skeletal muscle mass, declining strength and muscle atrophy are terms that describe a decrease in muscle size and functional strength. The changes in muscle size and ultimately strength levels are related to the loss of muscle fibers and shrinking of remaining fibers. Under normal conditions human muscle strength in women and men reaches its peak between the ages of 20-30 years, after which it remains virtually unchanged for another 20 years, if there is no disease or injury. After this point muscular performance deteriorates at a rate of about five per cent per decade, amounting to a 30 to 40 per cent loss of functional strength over the adult life span. Variations in the rate of loss reflect the diversity of occupations, physical activity backgrounds, the muscles used, and type of muscle contractions.

The upside for graceful aging is the ability of elderly individuals to respond to exercise with large gains in strength, mobility and physical fitness. Exercise studies have repeatedly demonstrated the capacity of older muscle to adapt to specifically designed training programs, resulting in gains in both strength and muscle size regardless of age or gender. Because the independent performance of many daily living activities is strength-dependent, the maintenance of muscle size and functional strength should play an important role in the training regime for older adults.

Hormone Health 

Hormones are the chemical messengers of the body that function to control and coordinate many of the body’s activities. Muscle development, growth and maturation, immune functions and perhaps even aging itself are among them. Unfortunately, like most chemicals, tissues, organs and organ systems in the body, hormones are not excluded from the changes and decline seen throughout the aging body. The lower levels of hormone production probably precede the accompanying visual changes. Ultimately, the changes in hormones accompany the changes in bone and muscle strength as well as the other way around.

As the human body inevitably advances toward old age it is becoming more evident that strength training and weight-bearing activity are providing the answers to slowing age-related changes in our bones, muscles and hormones.

Strength training provides the mechanical stress or “load” that stimulates the development of muscle and bone strength. The adaptation of muscles as a result of regular strength-training sessions and weight-bearing activity include strength changes and muscle mass improvement. A consequence of these improvements is the fact that the muscle is now capable of providing a stronger contraction to increase training loads. The advantage of this is that muscle contraction is the dominant source of skeletal loading that provides the mechanical stimulus to increase bone.

In contrast, physical inactivity has been shown as a contributing factor to the loss of bone, muscle mass and other health risks. The ideal exercise regime for maintaining or promoting bone, muscle and hormone health is strength training. Strength training can be site-specific, individualized, progressively overloaded and adjustable. Strength training also provides other benefits, such as improved balance and coordination.

Two important concerns for strength training are intensity and recovery. A minimum of two sessions a week for 45-60 minutes beginning at 70 per cent of the one repetition maximum (1RM) and building to 85 per cent 1RM would be appropriate. It is better to stand on the side of caution when beginning. Recovery becomes paramount if the training programs are to be effective for the older adult. Regular health checks and training program assessments are required to determine the efficiency of the training program. Preventive measures for bone and hormone loss, maintaining a physically active, healthy lifestyle and modification of risk factors for falls will yield benefits to overall health.

Returning to a physical activity program after an absence, or beginning a new training program, can be both intimidating and beneficial, especially for the untrained or inexperienced. After making the first and important decision to return to an exercise program, there are several basic guidelines to follow. The first is to consult with a physician about resuming a regular exercise program so he/she may determine overall health and be aware of conditions that may restrict exercise. With this information in hand, the next step is to discuss goals and needs with a qualified sports or exercise scientist/trainer. Strength training is one solution that can be used to alter the changes in bone strength, muscle strength and hormone levels that accompany aging.

Written for the American Collge of Sports Medicine by Brendan D. Humphries, Ph.D.

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Caffeine and Exercise Performance


ACSM current comment

Caffeine ingestion (3-9 mg/kg bw) prior to exercise increases performance during prolonged
endurance exercise and short-term intense exercise lasting approx. 5 minutes in the
laboratory. These results are generally reported in well-trained elite or recreational athletes,
but field studies are required to test caffeine’s ergogenic potency in the athletic world.
Caffeine does not appear to enhance performance during sprinting lasting less than 90
seconds, although research in this area is lacking. The mechanisms for improved endurance
have not been clearly established. Muscle glycogen sparing occurs early during endurance
exercise following caffeine ingestion but it is unclear whether this is due to increased fat
mobilization and use by the muscle. The positive effect of caffeine during exercise lasting
approx. 5 minutes is not related to the sparing of muscle glycogen. The ergogenic effects of
caffeine are present with urinary caffeine levels that are well below the IOC allowable limit
(12 ug/ml). This raises ethical issues regarding caffeine use in athletics. Should the practice
be condoned, as it is legal, or should it be discouraged, as it promotes the “doping mentality”
and may lead to more serious abuse? One solution would be to add caffeine to the list of
banned substances, thereby requiring athletes to abstain from caffeine ingestion 48-72
hours prior to competition and discouraging its use as a doping agent to increase
performance in the average population.


Caffeine may be the most widely used stimulant in the world. It is found in a variety of plants, dietary sources (including coffee, tea, chocolate, cocoa, and colas), and non-prescription medications. The average caffeine consumption in the USA is approximately 2 cups of coffee per day (200 mg); 10% of the population ingests more than 1000 mg per day. Caffeine is a socially acceptable, legal drug consumed by all groups in society.

Caffeine is often referred to as a nutritional ergogenic aid, but it has no nutritional value. Ingested caffeine is quickly absorbed from the stomach and peaks in the blood in 1-2 hours. Caffeine has the potential to affect all systems of the body, as it is absorbed by most tissue. The remaining caffeine is broken down in the liver and byproducts are excreted in urine.


Laboratory studies from the 1970’s suggested that caffeine enhanced endurance performance by increasing the release of adrenaline into the blood stimulating the release of free fatty acids from fat tissue and/or skeletal muscle. The working muscles use this extra fat early in exercise, reducing the need to use muscle carbohydrate (glycogen). The “sparing” of muscle glycogen made more available later in exercise to delay fatigue.

In the 1980’s, many studies found that caffeine did not alter exercise metabolism, and implied that it had no ergogenic effect, without actually measuring performance. A few reports did examine caffeine and performance during endurance exercise and generally found no ergogenic effect. By the end of the decade, it was suggested that caffeine did not alter metabolism during endurance exercise and may not be ergogenic.

Recent work reported that ingestion of 3-9 mg of caffeine per kilogram (kg) of body weight one hour prior to exercise increased endurance running and cycling performance in the laboratory. To put this into perspective, 3 mg per kg body weight equals approximately one mug or 2 regular size cups of drip-percolated coffee; and 9 mg/kg = approximately 3 mugs of 5-6 regular size cups of coffee. These studies employed well-trained, elite or serious, recreational athletes. Studies with untrained individuals cannot be performed due to their inability to reliably exercise to exhaustion.

The mechanism to explain these endurance improvements is unclear. Muscle glycogen is spared early during submaximal exercise following caffeine ingestion (5-9 mg/kg). It is unknown whether glycogen sparing occurs as a result of caffeine’s ability to increase fat availability for skeletal muscle use. Furthermore, there is no evidence supporting a metabolic component for enhancing performance at a low caffeine dose (3 mg/kg). Therefore, it appears that alterations in muscle metabolism alone cannot fully explain the ergogenic effect of caffeine during endurance exercise.


Research suggests that caffeine ingestion improves performance during short-term exercise lasting approximately 5 minutes at 90 to 100 percent of maximal oxygen uptake in the laboratory. This exercise intensity requires maximal provision of energy from both aerobic (oxygen requiring) and anaerobic (non-oxygen) sources. It is unknown if this finding applies to race situations. The reasons for the performance improvement may be a direct positive effect of caffeine on muscle anaerobic energy provision and contraction or a central nervous component related to the sensation of effort. Caffeine ingestion does not appear to improve sprint performance, but additional well-controlled laboratory and field studies are required to confirm this conclusion. Sprinting is defined as exercise that can be maintained from a few seconds to 90 seconds where most of the required energy is derived from anaerobic metabolism.


Caffeine Dose. Caffeine is a “controlled or restricted substance” as defined by the International Olympic Committee (IOC). Athletes are allowed up to 12 ug caffeine per milliliter of urine before it is considered illegal. The acceptable limit in sports sanctioned by the National Collegiate Athletic Association (NCAA) in the U.S. is 15 ug/ml urine. These high urinary limits are to allow athletes to consume normal amounts of caffeine prior to competition. A large amount of caffeine can be ingested before reaching the “illegal” limit. For example, if a 70 kg person rapidly drank about 3-4 mugs, or 5-6 regular size cups of drip-percolated coffee (~9 mg/kg bw) one hour before exercise, exercised for 1-1.5 hours and then gave a urine sample, the urinary caffeine level would only approach the limit (12 ug/ml). The odds of reaching the limit through normal caffeine ingestion are low, except where smaller volumes of coffee with very high caffeine concentrations are consumed. Therefore, an illegal urinary caffeine level makes it highly probable that the athlete deliberately took supplementary caffeine tablets or suppositories in an attempt to improve performance.

The optimal dose for maximizing the chance that exercise performance will be enhanced is ~3 – 6 mg/kg, where side effects are minimized and urine levels are legal. The side effects of caffeine ingestion include anxiety, jitters, inability to focus, gastrointestinal unrest, insomnia, irritability, and, with higher doses, the risk of heart arrhythmias and mild hallucinations. While the side effects associated with doses of up to 9 mg/kg do not appear to be dangerous, they can be disconcerting if present prior to a competition and may impair performance. Ingestion of higher doses of caffeine (10-15 mg/kg) is not recommended as the side effects worsen. It should also be noted that most studies have used pure caffeine rather than a caffeinated beverage or food. Thus, it is not certain that consuming the “equivalent dose of caffeine” as coffee, for example, will have the same result.

Diuretic Effect of Caffeine. Coffee and/or caffeine are often reported to be diuretics, suggesting that ingestion of large quantities could lead to poor hydration status prior to and during exercise.

However, the available literature does not support immediate diuretic effect as body core temperature, sweat loss, plasma volume and urine volume were unchanged during exercise following caffeine ingestion.

Ethical Considerations. It is easy for endurance athletes to improve performance “legally” with caffeine, as ergogenic effects have been reported with as little as 3 mg/kg body weight (bw). Even ingesting a moderate caffeine dose (5-6 mg/kg) is permissible. It has been suggested that caffeine should be banned prior to endurance competitions, requiring the athletes to abstain from caffeine approx. 48-72 hours before competition. This limitation would ensure that no athlete had an unfair advantage on race day, but would not prevent caffeine use in training. However, even if caffeine is banned in the future, what practice should athletes follow at present? For elite athletes, it is currently acceptable and reasonable to have their normal dietary coffee. However, if they deliberately take pure caffeine to gain an advantage on competitors, it is clearly unethical and is considered doping.

An equally important issue is the use of caffeine by the average active teenager or adult. Caffeine’s widespread use was demonstrated in a recent survey by the Canadian Centre for Drug Free Sport. The survey found that 27% of Canadian youths (11-18 years old) had used a caffeine-containing substance in the previous year for the specific purpose of enhancing athletic performance. Does caffeine act as a “gateway” drug for the young who then use dangerous substances? For the average, active teenager or adult who is exercising with the goals of enjoyment and self-improvement, using caffeine defeats these purposes. Proper training and nutritional habits are more sensible and productive approaches.

Written for the American College of Sports Medicine by Lawrence L. Spriet, Ph.D., FACSM (Chair) and Terry E. Graham, Ph.D., FACSM.

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