SUMMARYACSM Position Stand on The Recommended Quantity and Quality of Exercise for Developing and Maintaining Cardiorespiratory and Muscular Fitness, and Flexibility in Adults. Med. Sci. Sports Exerc., Vol. 30, No. 6, pp. 975-991, 1998. The combination of frequency, intensity, and duration of chr

http://myweb.facstaff.wwu.edu/chalmers/pdfs/acsm position stand - quantity and quality of exercise.pdf

ACSM Position Stand: The Recommended Quantity and Quality of Exercise for Developing and Maintaining Cardiorespiratory and Muscular Fitness, and Flexibility in Healthy Adults

SUMMARY Exertional heat illness can affect athletes during high-intensity or longduration exercise and result in withdrawal from activity or collapse during or soon after activity. These maladies include exercise associated muscle cramping, heat exhaustion, or exertional heatstroke. While certain individuals are more prone to collapse from exhaustion in the heat (i.e., not acclimatized, using certain medications, dehydrated, or recently ill), exertional heatstroke (EHS) can affect seemingly healthy athletes even when the environment is relatively cool. EHS is defined as a rectal temperature greater than 40-C accompanied by symptoms or signs of organ system failure, most frequently central nervous system dysfunction. Early recognition and rapid cooling can reduce both the morbidity and mortality associated with EHS. The clinical changes associated with EHS can be subtle and easy to miss if coaches, medical personnel, and athletes do not maintain a high level of awareness and monitor at-risk athletes closely. Fatigue and exhaustion during exercise occur more rapidly as heat stress increases and are the most common causes of withdrawal from activity in hot conditions. When athletes collapse from exhaustion in hot conditions, the term heat exhaustion is often applied. In some cases, rectal temperature is the only discernable difference between severe heat exhaustion and EHS in on-site evaluations. Heat exhaustion will generally resolve with symptomatic care and oral fluid support. Exercise associated muscle cramping can occur with exhaustive work in any temperature range, but appears to be more prevalent in hot and humid conditions. Muscle cramping usually responds to rest and replacement of fluid and salt (sodium). Prevention strategies are essential to reducing the incidence of EHS, heat exhaustion, and exercise associated muscle cramping.

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Exertional heat illness during training and competition

A model is proposed in which the development of physical exhaustion is a relative rather than an absolute event and the sensation of fatigue is the sensory representation of the underlying neural integrative processes. Furthermore, activity is controlled as part of a pacing strategy involving active neural calculations in a "governor" region of the brain, which integrates internal sensory signals and information from the environment to produce a homoeostatically acceptable exercise intensity. The end point of the exercise bout is the controlling variable. This is an example of a complex, non-linear, dynamic system in which physiological systems interact to regulate activity before, during, and after the exercise bout.

https://bjsm.bmj.com/content/bjsports/38/6/797.full.pdf

Evidence for complex system integration and dynamic neural regulation of skeletal muscle recruitment during exercise in humans

SUMMARYIt is the position of the American College of Sports Medicine that adequate fluid replacement helps maintain hydration and, therefore, promotes the health, safety, and optimal physical performance of individuals participating in regular physical activity. This position statement is based on a

ACSM Position Stand: Exercise and Fluid Replacement

This study was designed to show the general increase in perceived exertion, perception of aches or pain in the legs, heart rate (HR), and blood lactate, and the covariance between these variables during bicycle ergometer work, and to describe individual differences both within and between power levels by testing a large group (28 male students).

The increase of perceived exertion, aches and pain in the legs, heart rate and blood lactate during exercise on a bicycle ergometer.

During intensive exercise such as marathon running, heat is produced in the contracting muscles at rates in excess of 1100 W, on the order of 15 to 18 times of the basal metabolic rate. Practically all of this heat is rapidly transferred from the muscles to the blood and carried to the body core in the venous return. A heat production of this magnitude is sufficient to raise the body core temperature of an average-sized individual by 1' C every 5 minutes if no temperature regulatory mechanisms were activated. Since a marathon runner is able to sustain this level of exercise for 2 to 3 hours' with body core temperature maintained at a relatively constant level between 39 and 41\" C,*g it is evident that the temperature regulatory system must be highly efficient. It is well established that in the presence of a thermal load, thermal receptors in specialized sites within the hypothalamus sense the increased body temperature and in response direct an integrated reflex whereby the excess heat is transferred via increased cutaneous circulation to the skin surface, where it can be dissipated by physical means, primarily the evaporation of sweat. In this case the great amount of heat produced during running is balanced by the heat dissipated to the environment and the new steady state of internal body temperature is maintained until some new perturbation is introduced. In the following paragraphs we will describe studies that were intended to elucidate the characteristics and sensitivity of the temperature regulatory system in humans during exercise. Since the rate of heat storage (and hence the new steady state of internal body temperature) is primarily determined by the rapidity of the temperature regulatory response, most of our studies were conducted during the 20 to 30 minute initial transient of exercise.

Physiological defenses against hyperthermia of exercise

The relationships between some physical and physiological events, and perceived effort were studied at several equivalent work outputs (V) at two pedalling rates (30 and 60 rev·min−1). Subjects judged effort throughout a 4 min exercise bout. After 4 min at any sen it was always more effortful to pedal at 30 rev·min−1 even though there were no differences in VE, VO2 or integrated electromyography per minute (IEMG·min−1) between pedalling rates. Effort was related to VO2 and IEMG·min−1 but it was more effortful to pedal at 30 rev·min−1. Effort was also related to pedal resistance and IEMG of single contractions but was influenced by pedalling rate after 4 min of exercise. At any resistance it was more effortful to pedal at 60 rev·min−1, however, when effort was plotted as a function of resistance after 15 s, there was virtually no effect of pedalling rate. The rate effect grows with time from the onset of exercise and appears to be related to the central signal to the effort sense. The interaction of peripheral and central signals suggests a model of the effort sense during exercise.

https://link.springer.com/content/pdf/10.1007/BF00421773.pdf

Enzo Cafarelli

Papers

Physiological defenses against hyperthermia of exercise

Peripheral and central inputs to the effort sense during cycling exercise.