Page 89 - Color_Atlas_of_Physiology_5th_Ed._-_A._Despopoulos_2003

Physical Fitness and Training types of physical training strategies, and most
training programs use a combination of them.
The physical exercise capacity can be Motor learning, which increases the rate and
measured using simple yet standardized tech- accuracy of motor skills (e.g., typewriting).
niques of ergometry. This may be desirable in These activities primarily involve the CNS.
athletes, for example, to assess the results of Endurance training, which improves sub-
training, or in patients undergoing rehabilita- maximal long-term performance (e.g., run-
tion therapy. Ergometry assesses the effects of ning a marathon). The main objectives of en-
exercise on physiological parameters such as durance training are to increase the oxidative
.
Nerve and Muscle, Physical Work (performance) is expressed in watts (W) or to increase V O 2 max (! B, C). The resulting in-
capacity of slow-twitch motor units (! p. 58!,
O 2 consumption (V O 2 ), respiration rate, heart
e.g., by increasing the mitochondrial density,
rate (! p. 74), and the plasma lactate concen-
tration (! A). The measured physical power
increase the cardiac output and, consequently,
.
crease in heart weight allows higher stroke
W/kg body weight (BW).
volumes (! C) as well as higher tidal volumes,
In bicycle ergometry, a brake is used to adjust the watt
resulting in very low resting heart rates and
level. In “uphill” ergometry on a treadmill set at an
respiratory rates. Trained athletes can there-
angle α, exercise performance in watts is calculated
fore achieve larger increases in cardiac output
as a factor of body mass (kg)!gravitational accelera-
and ventilation than untrained subjects (! C).
– 2
tion g (m · s )!distance traveled (m)!sin α!1/
.
time required (s ). In the Margaria step test, the test
– 1
by the cardiovascular capacity, not the respira-
possible after a certain starting distance. Perform-
tory capacity. In individuals who practice en-
ance is then measured as body mass (kg)!g
2 subject is required to run up a staircase as fast as The V O 2 max of a healthy individual is limited
durance training, the exercise-related rise in
– 2
– 1
(m · s )!height/time (m · s ).
the lactate concentraton is also lower and oc-
Short-term performance tests (10–30 s) curs later than in untrained subjects (! A).
measure performance achieved through the Strength training improves the maximum
rapidly available energy reserves (creatine short-term performance level (e.g., in weight
phosphate, glycogen). Medium-term perform- lifting). The main objectives are to increase the
ance tests measure performance fueled by an- muscle mass by increasing the size of the
aerobic glycolysis (! p. 72). The maximum O 2 muscle fibers (hypertrophy) and to increase
.
consumption (V O 2 max) is used to measure the glycolytic capacity of type motor units
longer term aerobic exercise performance (! p. 58).
achieved through oxidation of glucose and free Excessive physical exercise causes muscle
fatty acids (! p. 74). soreness and stiffness. The underlying cause is
In strenuous exercise (roughly 2/3 the max- not lactic acid accumulation, but sarcomere
imum physical capacity or more), the aerobic microtrauma, which leads to muscle swelling
mechanisms do not produce enough energy, so and pain. The muscle ache, is a sign of micro-
anaerobic metabolism must continue as a par- inflammation (! D).
allel energy source. This results in lactacidosis Muscle fatigue may be peripheral or central.
and a sharp increase in the plasma lactate con- Peripheral fatigue ist caused by the exhaustion
centration (! A). Lactate concentrations of of energy reserves and the accumulation of
up to 2 mmol/L (aerobic threshold) can be metabolic products in the active muscle. This
tolerated for prolonged periods of exercise. is particularly quick to occur during postural
Lactate concentrations above 4 mmol/L (an- work (! p. 66). Central fatigue is characterized
aerobic threshold) indicate that the perform- by work-related pain in the involved muscles
ance limit will soon be reached. Exercise must and joints that prevents the continuation of
eventually be interrupted, not because of the physical exercise or decreased the individual’s
increasing lactate concentration, but because motivation to continue the exercise.
of the increasing level of acidosis (! p. 74).
Physical training raises and maintains the
76 physical exercise capacity. There are three
Despopoulos, Color Atlas of Physiology © 2003 Thieme
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