William L. Daniels

The influence of muscle metabolic characteristics on physical performance

SummaryThis study describes the influence of muscle fiber type composition, enzyme activities and capillary supply on muscle strength, local muscle endurance or aerobic power and capacity. Muscle biopsies were obtained from m. vastus lateralis in thirteen physically active men. Histochemical staining procedures were applied to assess the percentage of fast twitch (FT) fibers, muscle fiber area, and capillary density. Also, the activity of citrate synthase (CS), creatine kinase (CK), hexokinase (HK), lactate dehydrogenase (LDH), and phosphofructokinase (PFK) were analysed using fluorometrical assays. Peak torque at ‘low’ and ‘high’ angular velocities was measured during leg extension. Similarly, muscle fatigue (e. g. peak torque decline) and recovery from a short-term exercise task were measured during maximal, voluntary consecutive leg extensions. Aerobic power (

Effects of travel across time zones (jet-lag) on exercise capacity and performance.

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Physiological effects of a military training program on male and female cadets

) and aerobic capacity (e.g. onset of blood lactate concentration; OBLA), as defined by a blood lactate concentration of 4 mol · l−1 were measured during cycling. Peak torque at a high angular velocity was positively correlated with % FT area (p<0.001). Fatigue and recovery were correlated with LDH · CS−1 (p<0.001). WOBLA was best correlated with PFK and PFK · CS−1 (p<0.001). Hence, muscle strength was partly determined by fiber type composition whereas local muscle endurance, recovery and aerobic capacity reflect mainly capillary supply and the activity of key enzymes involved in aerobic and anaerobic metabolism.

Does fever or myalgia indicate reduced physical performance capacity in viral infections

SummaryMale infantry soldiers (n=34) were studied before, during, and after a 5-day simulated combat exercise. During the exercise, subjects were rated on their field performance by senior infantry non-commissioned officers. Prior to the exercise, direct measures of body composition and maximal oxygen uptake were obtained. Before and after the exercise the Army Physical Fitness Test and various measures of anaerobic capacity (Wingate and Thorstensson tests) and muscular strength (isometric and isokinetic) were obtained. Results showed no significant decrement in field performance during the exercise. Upper-body anaerobic capacity and strength declined following the exercise, al though the results for upper-body strength were not consistent on all measures. Field performance was significantly correlated with measures of upper-body anaerobic capacity and strength. Upper-body strength and anaerobic capacity appear to be important for infantry operations and subject to declines during combat operations.