Can excessive training impair metabolic health?
Exercise training can improve exercise performance, mitochondrial function, and blood sugar control. However, it’s well known by athletes that too much training (overtraining) can hinder performance. Can excessive exercise volume also have a detrimental impact on metabolic health?
This study investigated the effect of progressively increasing training loads on metabolic health. Participants performed increasing loads of HIIT for three weeks. The HIIT consisted of cycling exercise at 90-95% maximal oxygen consumption (blocks of 4 min followed by 3 min rest). The first week was light training (36 min HIIT), the second week was moderate training (90 min HIIT), and the third week was excessive training (152 min HIIT). Oral glucose tolerance tests were performed to determine glucose tolerance and muscle biopsies were taken to determine mitochondrial function.
Cycling performance, glucose tolerance and mitochondrial function were improved in the first two weeks of the intervention (i.e. light and moderate training). However, performance, glucose tolerance and mitochondrial function were all impaired following the excessive training week.
To further investigate glucose tolerance with high training loads, this study also investigated glucose control in elite athletes. In support of the previous findings, elite athletes showed impaired glucose control during a 24-h measurement period when compared to a matched control group.
This study does not advise against intensive exercise, as elite athletes have lower mortality rates when compared to the general population. However, the data suggest there may be an upper limit to the positive effects with even some negative effects at excessive volumes.
Next in the endurance exercise series:
Interval more anabolic than continuous cardio?
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