Exercise bout duration

During NCR a clear reduction of IMCL in both muscles was observed (about 20%, spectra not shown), which was even more prominent after M (about 50-60%, Fig. 28a). In contrast to this, IMCL were nearly unchanged after HM (Fig. 28b). The mean reduction of IMCL in all subjects is given in Fig. 28c. The studies show that decline of IMCL levels depends on exercise intensity, as a marked decrease in IMCL after exercise of similar duration is only observable at lower aerobic workloads (NCR vs. HM). IMCL reduction also depends on exercise duration, as shown by the greater decline after the marathon run (M = 225 min) compared to the non-competitive exercise bout (NCR =106 min). 

Several Important training variables are known to Influence the magnitude of the biochemical response. These Include the duration of the training program, the Intensity of the exercise effort, the duration of each exercise bout (mlnutes/day), and the frequency of exercise (l.e., days/week). 

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.

For those unable to sustain longer exercise periods, intermittent bouts can also be implemented at different times throughout the day. For those with low cardiorespiratory fitness, the duration of exercise can begin at any duration level with rest between bouts. The duration can increase progressively over a period of weeks until the desired goal is achieved. The rate of progression should be specific for each patient. 

Up to this point we have examined the influence of acute and chronic exercise on carnitine levels in the muscle, plasma, and urine. The hterature is fairly consistent in that there does not seem to be a depletion of total muscle carnitine and that an acute bout or chronic training does not change these levels. It is important to now focus on the performance aspect of these and other studies. The intent is to ascertain whether carnitine supplementation enhances performance as measured by such variables as VOj max, RQ, exercise duration, blood lactate concentrations, substrate metabolism, and glycogen sparing. There have been several studies that measured all or some combination of tliese markers, and they will be presented in ehronological order to help follow the progression of eamitine researeh. 

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