Sex Differences

For the same amount of muscles, no differences in strength between the sexes.
♀ posses smaller muscle fiber cross-sectional areas than ♂
 less muscle mass.
Sex Differences
For the same rate of work, trained ♀ generally have cardiac outputs similar to those of comparability trained ♂, but this is achieved through higher heart rates & lower stroke volumes.
Sex Differences
Sex Differences
Resistance training  major increase in strength (20% - 40%), similar to ♂.
In ♀ these gains are due more to neural factors, because increase in muscle mass is generally small.
Aerobic training  major increase in endurance capacity ( VO2max increases of 10 – 40%)
Physiological responses to exercise in the heat
During exercise in the heat, the heat loss mechanisms complete with the active muscle for more of the limited blood volume. Thus, neither area is adequately supplied under extreme conditions.
Though cardiac output may remain reasonably constant, stroke volume may decline, resulting in gradual upward drift in heart rate.
Physiological responses to exercise in the heat
Oxygen uptake also increases during constant rate exercise in the heat.
Sweating increases during exercise in the heat, and this can quickly lead to dehydration and excessive electrolyte loss. To compensate, the release of aldosterone and ADH increases, causing sodium and water retention, which can expand he plasma volume.
Heat acclimatization
Repeated exposure to heat stress causes a gradual improvement in your ability to lose excess heat. This process of adaptation is called “heat acclimatization”.
With heat acclimatization, the rate of sweating increases in areas that are well exposed and are the most efficient at promoting heat loss. This reduces skin temperature, which increases the thermal gradient from the internal to external body and promotes heat loss.
Heat acclimatization
Stroke volume increases with the acclimatization. This aids delivery of more blood to the active muscles and skin when necessary.
Heat acclimatization reduces the rate of muscle glycogen use, delaying the onset of fatigue.
Heat acclimatization
Heat acclimatization requires exercise in a hot environment, not merely exposure to heat.
The amount of heat acclimatization attained depends on the conditions to which you are exposed during each session, the duration of exposure, and your rate of internal heat production.
Physiological responses to exercise in the cold
Shivering (involuntary muscle contractions) increases metabolic heat production to help maintain or increase body temperature in the cold.
Nonshivering thermogenesis accomplishes the same goal, but through stimulation of the sympathetic nervous system and by the action of hormones such as thyroxin and the catecholamines.
Physiological responses to exercise in the cold
Peripheral vasoconstriction decreases the transfer of core heat to the skin, thus decreasing heat loss to the environment.
Body size is an important consideration for heat loss. Both increased surface area and reduced subcutaneous fat facilitate the loss of body heat to the environment. So those who have a small surface area-to-body mass ratio and those with more fat are less susceptible to hypothermia.
Physiological responses to exercise in the cold
Wind increases heat loss by convection and conduction, so this effect, known as wind chill, must be considered along with air temperature during cold exposure.
Immersion in cold water tremendously increases heat loss through conduction. Exercise generates metabolic heat to offset some of this loss.
Physiological responses to exercise in the cold
When muscle is cooled, it is weakened, and fatigue occurs more rapidly.
During prolonged exercise in the cold, as energy supplies diminish and exercise intensity declines, a person becomes increasingly susceptible to hypothermia.
Physiological responses to exercise in the cold
Exercise triggers release of catecholamines, which increase the mobilization and use of free fatty acid for fuel. But in the cold, vasoconstriction impairs circulation to the subcutaneous fat tissue, so this process is attenuated.
Cold acclimatization
Knowledge is limited, has not been studied well.
Repeated exposure to the cold, may alter peripheral blood flow & skin temperatures, allowing greater cold tolerance.