Water is the most essential component of the human body as it provides an important role in the function of cells. Important functions of water include transportation of nutrients, elimination of waste products, regulation and maintenance of body temperature through sweating, maintenance of blood circulation and pressure, lubrication of joints and body tissues, and facilitation of digestion.
More than half of the human body is composed of water, and it is impossible to sustain life without it.
Exercise produces an elevation in body temperature, which depends on the intensity and duration of exercise, environmental conditions, clothing worn, and metabolic rate. In order to get rid of the excess heat, your body secretes sweat, which is primarily composed of water and electrolytes such as sodium.
The evaporation of sweat is the primary mechanism of heat loss during exercise. Exercise can lead to substantial water and electrolyte loss from sweat leading to dehydration and, in cases of excessive fluid intake, hyponatremia (low sodium in the blood). However, considerable variability exists from person to person with regard to sweat loss. Therefore, the fluid and electrolyte requirements needed for the athlete are variable from person to person as well. If water and electrolytes are not replaced from these losses, the athlete will have a decrease in performance and perhaps an adverse effect on his or her overall health.
Thirst is a signal that your body is headed toward dehydration. Therefore, it is important to drink before you feel thirsty and to drink throughout the day. Thirst is not a good indicator of hydration and should not be used to monitor hydration status. One way to check your hydration status is to weigh yourself before and after exercise. The before-exercise measurement is best as a nude weight first thing in the morning after urinating. Comparing your body weight before and after exercise can be used to estimate your sweat loss and your fluid requirements. Any weight loss is likely from fluid loss, so drinking enough to replenish these losses will maintain hydration.
The table below shows us that over a one percent loss in body weight indicates dehydration and over five percent indicates serious dehydration. These fluid losses need to be replaced.
% Body Weight Change
Well Hydrated -1 to +1%
Minimal Dehydration -1 to -3%
Significant Dehydration -3 to -5%
Serious Dehydration > -5%
Another way to check hydration status is the urine color test. A large amount of light-colored urine means you are well hydrated. The darker the color, the more dehydrated you are.
Dehydration is the loss of fluids and salts essential to maintain normal body function. Dehydration occurs when the body loses more fluids than it takes in.
Dehydration can lead to:
- Muscle fatigue
- Loss of coordination
- Inability to regulate body temperature
- Heat illness (e.g., cramps, heat exhaustion, heat stroke)
- Decreased energy and athletic performance
Moderate caffeine intake does not affect hydration status or urine output. However, alcohol will increase your urine output and decrease hydration. Enhancing palatability of a fluid will help to encourage fluid consumption. This can be done with proper flavoring, proper salt (sodium) content and drinking a cold beverage (15-21 degrees Celsius).
Carbohydrates within a sports beverage help to replenish your sugar (glycogen) stores and electrolytes help to accelerate rehydration. Sports beverages for use during prolonged exercise should generally contain four to eight percent carbohydrate, 20-30 meq/L of sodium, and 2-5 meq/L of potassium. The need for carbohydrates and electrolytes within sports beverages increases with prolonged activity.
Carbohydrate consumption helps to sustain and improve exercise performance during high-intensity exercise longer than one hour as well as lower-intensity exercise for longer periods. You should ingest one-half to one liter of a sports drink each hour to maintain hydration. Also, sports drinks should not exceed a carbohydrate concentration of eight percent.
HYDRATION BEFORE EXERCISE
Check your hydration status before exercise because there is a wide variability in fluid needs for each person.
- Drink 16-20 fluid ounces of water or sports beverage at least four hours before exercise.
- Drink 8-12 fluid ounces of water 10-15 minutes before exercise.
Consuming a beverage with sodium (salt) and/or small meal helps to stimulate thirst and retain fluids.
HYDRATION DURING EXERCISE
- Drink 3-8 fluid ounces of water every 15-20 minutes when exercising for less than 60 minutes.
- Drink 3-8 fluid ounces of a sports beverage (5-8 percent carbohydrate with electrolytes) every 15-20 minutes when exercising greater than 60 minutes.
Do not drink more than one quart/hour during exercise.
HYDRATION GUIDELINES AFTER EXERCISE
Obtain your body weight and check your urine to estimate your fluid losses. The goal is to correct your losses within two hours after exercise.
Drink 20-24 fluid ounces of water or sports beverage for every one pound lost
Overhydration, also called water intoxication, is a condition where the body contains too much water. This can result in behavioral changes, confusion, drowsiness, nausea/vomiting, weight gain, muscle cramps, weakness/paralysis and risk of death.
In general, overhydration is treated by limiting your fluid intake and increasing the salt (sodium) that you consume. If overhydration is suspected, you should see your doctor for appropriate lab tests and treatment. You should not consume more than one liter per hour of fluid.
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Reprinted with permission of the American College of Sports Medicine. Copyright © 2011 American College of Sports Medicine. This brochure is a product of ACSM’s Consumer Information Committee.
Fotografía de Darwin Bell, usada bajo licencia de Creative Commons
En diciembre del 2013 el American College of Sports Medicine (ACSM) publicó los resultados de la encuesta sobre las tendencias en fitness alrededor del mundo. En total 3,815 profesionales —desde entrenadores físicos certificados hasta expertos en fisiología del ejercicio— respondieron la encuesta. Colombia se encuentra en la lista de los países participantes que incluye también a Brasil, Costa Rica, Perú, México, Australia, el Reino Unido, Singapur, España, Holanda y E.E.U.U., entre muchos otros.
TOP 20 FITNESS TRENDS FOR 2014
1. High-Intensity Interval Training (HIIT)*
2. Body Weight Training
3. Educated, Certified, and Experienced Fitness Professionals
4. Strength Training
5. Exercise and Weight Loss
6. Personal Training
7. Fitness Programs for Older Adults
8. Functional Fitness
9. Group Personal Training
11. Children and Exercise for the Treatment/Prevention of Obesity
12. Worksite Health Promotion
13. Core Training
14. Outdoor Activities
15. Circuit Training
16. Outcome Measurements
17. Wellness Coaching
18. Sport-Specific Training*
19. Worker Incentive Programs
20. Boot Camp
Tomado de: ACSM’S Health & Fitness Journal; November/December 2013 – Volume 17 – Issue 6 – p 10-20. doi: 10.1249/FIT.0b013e3182a955e6
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Fotografía de Living Fitness UK , usada bajo licencia Creative Commons
ACSM Current Comment
A cold is an inflammation of the upper respiratory tract caused by a viral infection. The common cold is probably the most frequently occurring illness in humans worldwide. More than 200 different viruses cause colds, and rhinoviruses and coronaviruses are the culprits 25-60 percent of the time. Rhinovirus infections often occur during the fall and spring seasons, while the coronavirus is more common during the winter.
The U.S. Centers for Disease Control and prevention estimates that over 425 million colds and flus occur annually in the United States, resulting in $2.5 billion in lost school and work days, and in medical costs. The average person has two or three respiratory infections per year. Young children suffer from six to seven annually.
How does one catch a cold?
Although still a matter of controversy, growing evidence suggests that at least among adults, cold viruses are passed from person to person primarily by being inhaled into the nose and air passageways (i.e., spread through the air). Viruses can be spread by direct contact with wet nasal discharge, but this may be rare, except perhaps in settings such as day care centers. Severe colds transmit viruses more readily than mild ones because a greater amount of virus is passed into the air by coughing and sneezing. Thus, to hinder the spread of cold viruses, coughs, sneezes and “nose-blows” should be smothered with clean handkerchiefs or facial tissues. It is also a very good idea to wash viruses off the hands with soap and water, and to disinfect one’s surroundings.
Damp, cold or drafty weather does not increase the risk of getting a cold. According to most cold researchers, cold or bad weather simply brings people together indoors, which leads to more person-to-person contact.
Doctors often quip that a cold lasts seven days without treatment, and one week with it. Most nonprescription medications, including antihistamines, decongestants, cough medicines, and analgesics provide only temporary relief of symptoms. These medications can make one feel more comfortable while the body’s immune system gears up to fight off the infection. To get rid of the cold, the immune system must make enough antibodies to destroy the viruses, a process that takes three to four days. Antibiotics that fight bacteria have no value in the treatment of the uncomplicated common cold which is caused by a virus.
Even the old standby – inhaling steam — has little or no beneficial effect on cold symptoms. Vitamin C does not prevent colds, according to most researchers, but may slightly reduce the severity and duration of symptoms. Resting, drinking plenty of hot fluids, and seeking comfort from over-the-counter cold remedies is still all that can be done to treat most colds.
Keeping the immune system in good shape
Whether one gets sick with a cold after a sufficient amount of the virus has entered the body depends on many factors that affect the immune system. Aging, cigarette smoking, mental stress, poor nutrition, and lack of sleep have all been associated with impaired immune function and increased risk of infection.
Based on current knowledge, good immune function can be maintained by eating a well-balanced diet, keeping life stresses to a minimum, avoiding chronic fatigue, and obtaining adequate sleep. Immune function is suppressed during periods of very low caloric intake and quick weight reduction, so weight loss should be gradual to maintain good immunity.
Can a walk each day keep colds away?
People who exercise report fewer colds than their inactive peers. For example, one recent survey revealed that 61% of 700 recreational runners reported fewer colds since beginning to run, while only 4 percent felt they experienced more. In another survey of 170 experienced runners who had been training for 12 years, 90% reported that they definitely or mostly agreed with the statement that they “rarely get sick.”
To test this belief scientifically, two well-controlled studies with young and elderly women were conducted. In both studies, women in the exercise groups walked briskly 35-45 minutes, five days a week, for 12-15 weeks, with the control groups remained physically inactive. The results were in the same direction reported by fitness enthusiasts — walkers experienced about half the days with cold symptoms as the sedentary controls.
Other research has shown that during moderate exercise, several positive changes occur in the immune system. Although the immune system returns to pre-exercise levels very quickly after the exercise session is over, each session represents a boost that appears to reduce the risk of infection over the long term.
Can too much exercise hurt?
Among elite athletes and their coaches, a common perception is that heavy exertion reduces resistance to colds. During the Winter and Summer Olympic Games, clinicians report that “upper respiratory infections abound” and that “the most irksome troubles with athletes are infections.”
To determine whether these anecdotal reports were true, 2,311 marathon runners who ran the 1987 Los Angeles Marathon were studied. During the week following the race, one out of seven runners became sick, which was about five times the rate of runners who trained for, but did not run, the Marathon. During the two-month period before the race, runners training more than 60 miles a week doubled their odds for sickness compared to those training less than 20 miles a week. Researchers in South Africa have also confirmed that after marathon-type exertion, runners are at a high risk for sickness.
The immune systems of marathon runners have been studied under laboratory conditions before and after running 2-3 hours. A steep drop in immune function occurs lasting at least 6-9 hours. Several exercise immunologists believe this allows viruses to spread and gain a foothold.
Rest or exercise when sick?
Most clinical authorities in the area of immunology recommend:
- If one has common cold symptoms (e.g., runny nose and sore throat without fever or general body aches and pains), intensive exercise training may be safely resumed a few days after the resolution of symptoms.
- Mild-to-moderate exercise (e.g., walking) when sick with the common cold does not appear to be harmful. In two studies using nasal sprays of a rhinovirus leading to common cold symptoms, subjects were able to engage in exercise during the course of the illness without any negative effects on severity of symptoms or performance capability.
- With a symptom complex of fever, extreme tiredness, muscle aches, and swollen lymph glands, 2-4 weeks should probably be allowed before resumption of intensive training.
- In general, if the symptoms are from the neck up, moderate exercise is probably acceptable and, some researchers would even argue, beneficial, while bed rest and a gradual progression to normal training are recommended when the illness is systemic. If in doubt as to the type of infectious illness, individuals should consult a physician.
Although more research is needed, the American College of Sports Medicine (ACSM) supports the viewpoint that moderate physical activity (30 minutes a day, on most, if not all days of the week) exerts less stress on the immune system than does prolonged and intense exercise. Regular and moderate exercise lowers the risk for respiratory infections, a finding consistent with previous reports from ACSM urging people to exercise moderately for enhancement of health and disease prevention. Athletes who must train hard for competition can lower their risk of respiratory infection by following the guidelines listed in this report for keeping the immune system in good shape.
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Running shoes should be selected after careful consideration. With so many brands and styles of shoes on the market today, it is important to find the best fit for your feet and your needs.
Consider the following when choosing a running shoes:
- Shoe size: the most common mistake in shoe selection is picking the wrong size. Be sure the shoe fits after break-in.
- Past experiences with shoes.
- Problems with your current shoes.
- Biomechanical needs (arch type, pronation, orthopedic injuries).
- Environmental conditions.
- Running and racing requirements.
FINDING A SHOE TO FIT YOUR FOOT CHARACTERISTICS
Carefully select shoes that fit the length and width of your feet. Determine what shoe shape you require based on your foot type. The wet test can be used to determine your foot type. Moisten your foot with water, and stand on any surface that will leave an imprint of your foot.
Normal Arch: A normal foot has a normal-sized arch and leaves an imprint that has a flare but shows the forefoot and heel connected by a wide band. A normal foot lands on the outside of the heel then rolls inward (pronates) slightly to absorb shock. Runners with a normal foot and normal weight are usually considered biomechanically efficient. Stability shoes work best for a normal foot and normal arch.
Low Arch: Flat feet have a low arch and leave a nearly complete imprint of the sole of the foot, indicating an overpronated foot that strikes on the outside of the heel and rolls inward excessively. Motion-control shoes work best for a flat foot with a low arch.
High Arch: High-arched feet leave an imprint showing a very narrow band connecting the forefoot and heel. This type of foot is underpronated and is not an effective shock absorber. Cushioned shoes work for a rigid foot with a high arch. Old shoes also show a pattern of wear that helps determine running style. Examine the soles of your shoes for a pattern of wear. Next, put your shoes on a table and look from the back of the shoe to the heel. If your shoe tilts to the inside, you may have a low arch. If your shoe tilts to the outside, you may have a high arch.
GUIDELINES FOR PURCHASING SHOES
Purchase running shoes from a good running shoe store or from someone knowledgeable about matching the correct type of shoe to your foot type and stride pattern. They can help you find the perfect fit that meets your needs.
Watch for shoes with excessive wear. Worn shoes often amplify a foot problem, and injuries can occur when a shoe is worn too long before it is replaced.
Analyze the need to purchase new shoes based on the number of miles on your old shoes, not by the amount of tread left on the outer soles. Most estimates place midsole breakdown, and increased potential for injury, between 400-500 miles. For some, this means replacing shoes before they show major wear.
OTHER RUNNING SHOE CONSIDERATIONS
Most people (85 percent) wear shoes that are too small. Shoe size varies among manufacturers. Have the shoe clerk help you select the correct shoe size. The shoe should have adequate room at the widest part of the foot. The shoe shouldn’t be tight, but it shouldn’t slide around either. Your heel should also fit snugly into the rear of the shoe.
Try shoes on later in the day, and bring the socks you normally run in. Try on several pairs of shoes in the category closest to your foot type. Make sure you try on both shoes since the sizes of your feet can be slightly different, and keep them on your feet for about ten minutes to make sure they are comfortable. Most good stores will allow you to run up and down the block to experience what running will feel like in the shoes.
Consider purchasing two pairs of running shoes. Alternating their use increases the life expectancy of each pair.
Once you’ve purchased new shoes, run easily in the shoes for a short distance. It is important to allow sufficient time, between 60-70 miles, to break in the new pair.
After you have wisely selected your new running shoes, take them home, put them on and enjoy the run!
Reprinted with permission of the American College of Sports Medicine. Copyright © 2011 American College of Sports Medicine. This brochure was created and updated by Shannon Crumpton and is a product of ACSM’s Consumer Information Committee. Visit ACSM online at www.acsm.org.
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ACSM current comment
Regular exercise is an important component of a healthy lifestyle. The American College of Sports Medicine, the American Heart Association, and other prominent organizations have issued recommendations to encourage individuals to establish and maintain participation in an exercise program. A potential impediment to an exercise program is the conflict that can be created by a business trip, which is a common event for many Americans. While it is not advisable for an individual to begin an exercise program while on a business trip, it is recommended that exercise habits be maintained while traveling.
Business trips can create a number of conflicts with your exercise program. It is important to recognize potential limitations so that you can plan accordingly and allow yourself to keep up your regimen. Here are some modifications in your exercise program that you might consider while traveling on business:
1. Consider exercise area and/or facility availability in your selection of lodging. If your exercise program includes a running component, you should be aware of restrictions that could exist in some urban areas. Ask hotel personnel for suggestions. If safe running routes are not available, you may find treadmill facilities in the hotel. Some hotels offer in-house exercise areas that might include weight training equipment, a swimming pool, and cardiovascular conditioning equipment. In some cities, perhaps a downtown athletic club will have an agreement with certain hotels whereby guests may use their facilities.
To prevent the muscular soreness that sometimes accompanies exercising new muscle groups or exercising differently (i.e. exercise equipment to which you are not accustomed), you may wish to reduce exercise intensity and duration. You may also consider packing such small pieces of exercise equipment as a jump rope or resistance bands.
2. Plan your trip schedule to include time for exercise. Business trips are fraught with time-crunched schedules and meetings and lunches that leave little extra time for the business traveler. However, there are a number of benefits to including time for exercise in your business trip itinerary. Exercise is known to be a stress reliever. Additionally, the distraction may even help you concentrate better and have the energy and focus to be more productive later. If a meeting is a must, then take attendees out for some exercise! This may provide a more informal setting to discuss matters while allowing you to maintain your exercise schedule.
3. Understand how reduced exercise time affects your fitness level. A common concern of exercisers who know they will not be able to exercise at all or as much due to restrictions imposed by their business trip is that they will suffer a reduction in their physical fitness level. It is important to understand that it is much easier to maintain your current level of fitness than it is to improve your fitness level. Current evidence suggests that you can take up to a week off from exercise training without any significant reduction in your fitness level. During longer trips you should be able to maintain your fitness with a regimen of either aerobic or strength training or both amounting to only twice a week, particularly if you maintain your exercise training intensity during this period of reduced training.
In conclusion, with advance planning and the willingness to make modifications to your exercise program, it is reasonable to incorporate exercise time into the schedule of a business trip. Because travel can be so disruptive to your normal schedule as well as other adjustments you must make (e.g., sleeping accommodations, food), this is NOT the best time to work on increasing your fitness level. Instead, the goal should be maintenance of your current fitness level.
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ACSM current comment
Around the world in health clubs on the walls beside treadmills, stationary bikes and step machines, one often sees a scale going from 6-20. This is called an RPE Scale, which stands for “Rate of Perceived Exertion.” It is a psychophysiological scale, meaning it calls on the mind and body to rate one’s perception of effort. Understanding the meaning and use of this chart will benefit the average fitness enthusiast.
The RPE scale measures feelings of effort, strain, discomfort, and/or fatigue experienced during both aerobic and resistance training. One’s perception of physical exertion is a subjective assessment that incorporates information from the internal and external environment of the body. The greater the frequency of these signals, the more intense are the perceptions of physical exertion. In addition, response from muscles and joints helps to scale and calibrate central motor outflow commands. The resulting integration of feedforward-feedback pathways provides fine-tuning of the exertional responses.
Perceived exertion reflects the interaction between the mind and body. That is, this psychological parameter has been linked to many physiological events that occur during physical exercise. These physiological events can be divided into respiratory/metabolic (such as ventilation and oxygen uptake) and peripheral (such as cellular metabolism and energy substrate utilization.) Previous studies have demonstrated that an increase in ventilation, an increase in oxygen uptake, an increase metabolic acidosis or a decrease in muscle carbohydrate stores are associated with more intense perceptions of exertion. The scale is valid in that it generally evidences a linear relation with both heart rate and oxygen uptake during aerobic exercise.
How is perceived exertion measured?
The level of perceived exertion is often measured with a 15 category scale that was developed by the Swedish psychologist Gunnar Borg. The Borg scale is shown below:
- 6 No exertion at all
- 7 Extremely light
- 9 Very light
- 11 Light
- 13 Somewhat hard
- 15 Hard (heavy)
- 19 Extremely hard
- 20 Maximal Exertion
© Gunnar Borg 1985
The Borg scale is simple to understand and very user-friendly. However, to use it effectively, it is necessary to adhere to the standard guidelines in measuring perceived exertion. These guidelines are:
1) It should be clear to either the client, patient, or athlete that perceived exertion is a method to determine the intensity of effort, strain, and/or discomfort that is felt during exercise;
2) The range of sensations must correspond to the scale. For example, number 6 should be made in reference to the feelings during rest, whereas number 20 should refer to the maximal level of exertion;
3) Either the RPE should be made specific to the overall body perception or the perception derived from a certain anatomical region of the body such as chest, arms and/or legs. Typically, individuals interested in monitoring the stress of a workout use RPE ratings.
4) It is important to know that when rating one’s perception of exertion there is no right or wrong
answer for the rating. However, the individual must clearly understand the meaning of the descriptors, so careful explanation of the scale is necessary before using.
How can ratings of perceived exertion be used?
Due to its reasonably linear relation with oxygen uptake and heart rate, RPE can be used to guide the progression of a graded exercise test. This is accomplished by providing subjective confirmation that end-points of the test have been achieved once the terminal rating is reported or by signaling the relative metabolic stress at a given time during the test. Based upon the fact that RPE’s positively correlate to power output over a wide range of intensities, they can also be used to predict aerobic power in a manner analogous to the way that heart rate is employed in submaximal testing.
Ratings of perceived exertion can also be used to prescribe and monitor exercise intensity during a workout. A common approach is to periodically ask a person to rate his or her perceived exertion for a given exercise intensity during a stress test and then match it to an appropriate exercise intensity prescription. Attempting to keep the RPE within a training range similar to heart rate training ranges can be effective. Using this procedure, the target RPE ratings are based upon prior test results, and the person is requested to produce intensity perceived to be similar to the target rating during a workout. The key is close approximation to heart rate in aerobic exercise, where the RPE scale is most often used.
A question is sometimes raised as to whether the intensity produced based on perceptual ratings is actually what it is supposed to be. Several recent studies have attempted to answer this question. These studies have used oxygen uptake as an objective variable and found no difference between the oxygen uptake that was estimated from the prior test results and oxygen uptake that was produced during a subsequent workout. This finding suggests that using a “target RPE” as a guide to regulate exercise intensity is valid.
It is important to note that using the RPE can be especially important in two situations. If heart-rate measurement is difficult for some reason, or if the individual is on medication that alters normal heart rate response to physical stress, RPE can be an excellent tool to regulate and monitor intensity. The RPE scale continues to be a useful tool, offering subjective reflection of physiological responses during physical exercise, and enabling the individual to regulate effort to gain maximum benefit.
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ACSM current comment
As athletes strive to improve their performance through effective training techniques, so too can workers benefit from optimally planned exercise training programs designed to boost occupational physical performance. Similar to athletics–where skill and fitness demands vary between that of the recreational and the professional athlete–occupational physical demands can vary among employment settings. Physically demanding occupations, such as those found in the armed services, emergency rescue professions, and construction and warehouse industries, require a high degree of physical fitness. Job performance in these occupations can be augmented by participation in formal exercise programs targeted at improving the musculoskeletal and/or cardiorespiratory systems.
Even less physically demanding occupations such as computer or clerical work can benefit from fitness and flexibility training. Tasks involving prolonged and repetitive pushing and pulling, holding, carrying, and lifting can lead to cumulative trauma disorders such as lower back pain, sprains, strains, carpal tunnel syndrome and neck pain. Physical training can be effectively used as both a prevention and rehabilitation tool in occupational settings. In addition to the well-known health benefits of being physically fit, physical training interventions can increase worker productivity by overcoming limitations in job performance due to inadequate muscle strength, power, endurance or aerobic capacity. Physical training can also prevent mismatches between job demands and physical capacities and decrease lost time due to injury-related absenteeism.
Conducting a Job Analysis
The first step in physical training program design is the completion of a comprehensive job analysis. This analysis should identify the most physically demanding and frequently occurring job tasks (critical job tasks). It will help to refer to written job descriptions and training manuals, observe individuals performing the job and interview subject-matter experts (e.g., ergonomists and occupational therapists). Once the critical physically demanding tasks have been identified, additional information regarding the tasks must be recorded to include mass and distance of loads handled, forces and torques exerted, frequency and duration of task performance, and equipment used to complete the job task. Information specific to the worker must also be recorded, such as body position, movement, and muscle groups employed while performing the task. This information is then used to determine the requisite energy systems and fitness components needed for successful job performance. Based on this information, a physical training program to improve job performance can be developed.
Before initiating a rigorous physical training program, it is essential that employees obtain medical approval for exercise.
Types of Physical Training for Improved Occupational Performance
Physical training programs for improving occupational physical performance typically assume one of two forms: 1) job- or task specific training and 2) generalized physical fitness training. Task-specific training is accomplished by performing the physically demanding tasks of the job. This must be done in a progressive manner. For example, if the main physically demanding task of a given occupation is to lift 20 boxes weighing 40 kg each from a pallet onto a waist-high shelf, this may be beyond the physical capacity of a new employee. The new worker may need to perform fewer lifts or may take longer to complete the task. Simply performing this task is a form of task-specific training. Once a worker is able to perform this task satisfactorily, the intensity of the exercise can be progressively increased to provide a continual training effect. This can be accomplished by manipulating the load lifted (resulting in strength gains), the lifting rate (resulting in aerobic gains), or the total number of repetitions (resulting in muscular endurance gains).
As the physical capacity of the worker increases (be it strength, cardiovascular endurance, or muscular endurance), the percentage of an individual’s maximum capacity utilized during the job task decreases. This, in turn, decreases the likelihood or risk of injury for that individual. Task-specific training is valid, and may provide improvement in task performance. The drawback is that it may be difficult and expensive to set up. A generalized physical fitness-training program is developed to improve employees’ overall health and physical fitness. The program emphasizes specific muscle groups and energy pathways needed for optimal job performance. For example, a job such as a luggage handler at an airport would involve moving many pieces of heavy luggage from a cart onto a belt, or from a moving belt into the belly of the plane. The periods of rapid lifting are followed by a short rest period while the handler drives the luggage to the next location.
This task is likely to have high strength and aerobic demands, and the individual may be required to work in confined postures. In this case, a general physical fitness program would involve progressive resistance exercise to increase strength and muscular endurance, as well an aerobic training component to improve aerobic capacity. The advantage of a general physical fitness training program is that it increases overall physical capacity and fitness of the individual. The training program is not narrowly focused, thus avoiding muscular imbalance. Increased physical capacity also may be generalized to other tasks. In other words, the employee may improve performance of other tasks, not just the one they were trying to improve. Generalized physical fitness training using standard exercise equipment reduces risk of injury compared with job-specific training. Ideally, a generalized physical fitness-training program is conducted in a corporate-owned or off-site fitness facility under the supervision of an experienced and certified allied health professional with a thorough knowledge of exercise training. One drawback to generalized physical fitness training is that the improvement in job performance is not so great as those obtained from task-specific training. The fact that improved performance may transfer to other tasks may offset this drawback.
Principles and Recommendations for Program Design
In designing a physical training program for improving occupational performance, several fundamental program-design variables should be considered:
- exercise selection and order
- equipment used
- rest intervals
The main factors influencing these variables are the initial fitness and training status of the worker and the desired outcome and goals of the program (i.e., muscle strength, power, endurance, aerobic capacity, and motor performance).
Jobs with little variation and a high skill or technical component will show the greatest improvements with task-specific training programs, while jobs requiring a variety of body movements and utilizing the various components of muscle fitness will benefit mostly from general fitness programs. The worker or “occupational athlete” can derive as much benefit in terms of improved performance as the Olympic athlete can by participating in optimal physical training programs.
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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.
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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