High-intensity exercise

A variable-speed drive is usually used on the feed and cross-belt drives to exercise control in separator operation, although the speed is not usually changed once the optimum operating condition is estabUshed. Feed rates and the selection of the number of magnetic poles are usually deterrnined by preliminary laboratory tests. The mineral types involved in the feed largely determine the number of poles selected. High intensity cross-belt separators are frequendy used in combination with induced-roU or electrostatic separators. 

Fatigue in Intact Skeletal Muscle of Human Subjects During High Intensity Exercise 247 Muscle Metabolism During Electrically Evoked High Intensity Contraction 248... 

FATIGUE IN INTACT SKELETAL MUSCLE OF HUMAN SUBJECTS DURING HIGH INTENSITY EXERCISE... 

Figure 4. Ten bouts of high intensity cycle exercise, each with a duration of 6 sec and with 30 sec rest periods between bouts were performed on a given day. The entire exercise protocol was performed on four separate days by each subject (n = 8), before and after placebo and creatine supplementation. Mean power output was 882 watts. Upper panels (A1 and B1) demonstrate mean revolutions per min during the 0-4 sec period of each bout and the lower panel (A2 and B2) during 4-6 sec of each bout. The left panels (A1 and A2) show results before (o) and after (x) placebo and the right panels (B1 and B2) before (o) and after (x) creatine supplementation. The study was performed in a double blind manner.

This categorization of relative whole body intensity is also valuable in distinguishing between high intensity and submaximal exercise. Exercise intensities or power outputs at or above 100% VO2 max are generally considered high intensity. These intensities require muscle contractions that generate -40-100% of the force... 

Balsom, P.D., Ekblom, B., Soderlund, K., Sjodin, B., Hultman, E. (1993). Creatine supplementation and dynamic high intensity intermittent exercise. Scand. J. Med. Sci. Sports (in press). 

Somewhat of a dichotomy exists in the research literature pertaining to caffeine s ergogenic potential to enhance short-term, intense exercise. In general, laboratory research (in vitro/in situ) has consistently demonstrated positive results related to caffeine s ability to generate increased muscular force. Human studies have consistently been suggestive of no significant effects on short-term, high intensity performance. There have been a... 

Williams, J. FT, Caffeine, neuromuscular function and high-intensity exercise performance, Journal of Sports Medicine and Physical Fitness, 31, 481, 1991. 

Caffeine increases the capacity of skeletal muscle. This effect is probably due to the release of intracellular Ca2+, and is observable in human performance. The contribution of central effects is also likely. Whether caffeine actually benefits exercise is contested (Spriet 1995 Dodd et al. 1993). Research does not consistently support caffeine enhancement of performance during high-intensity, short-term exercise. There is some evidence to suggest benefit during prolonged, moderate-intensity exercise. 

Fast-twitch muscle fibers have a high capacity for anaerobic glycolysis but are quick to fatigue. They are involved primarily in short-term, high-intensity exercise. Slow-twitch muscle fibers in arm and leg muscles are well vascularized and primarily oxidative. They are used during prolonged, low-to-moderate intensity exercise and resist fatigue. Slow-twitch fibers and the number of their mitochondria increase dramatically in trained endurance athletes. 

Short bursts of high-intensity exercise are supported by anaerobic glycolysis drawing on stored muscle glycogen. 

During very brief but very high-intensity exercise (sprinting, running upstairs), when there is not sufficient time for the arterioles to dilate to permit increased blood flow to the muscle. 

Most team games (e.g. soccer, rugby, hockey, football) and some individual sports (e.g. squash, tennis) involve intermittent high-intensity bursts of exercise interspersed with rest periods (i.e. mostly less intense periods), although the whole period of activity can be very long. These are known as multiple sprint sports. In experiments that involved a study of short bursts of activity followed by short rest periods, repeated for 30 minutes, the increase in blood... 

McMurray RG, Brown CF. The effect of sleep loss on high intensity exercise and recovery. Aviat Space Environ Med 1984 55 1031-1035. 

Hill DW, Borden DO, Damaby KM, Hendricks DN. Aerobic and anaerobic contir-butions to exhaustive high intensity exercise after sleep deprivation. J Sports Sci 1994 12 455 161. 

Jacobs I, Bell D. Modafinil prolongs time to exhaustion during high intensity sub-maximal exercise (abstr). Med Sci Sports Exerc 1997 29(suppl 5) S39. 

Ortega, E., Rodriguez, M J., Barriga, C., and Fomer, M.A. 1996. Corticosterone, prolactin and thyroid hormones as hormonal mediators of the stimulated phagocytic capacity of peritoneal macrophages after high-intensity exercise. Int J Sports Med 17 149-155. 

---