A small study from the US Department of Agriculture reports that low zinc might be the root cause of poor muscle strength and impaired cardiorespiratory and metabolic responses during and after exercise. This trial measured the effects of low versus high zinc intake on the physical performance of 14 men, aged 20 to 31 years. While the role of zinc during exercise is not fully understood, some zinc-containing enzymes are believed to regulate energy expenditure.

The participants were split into two groups, each following diets containing either 3.8 mg or 18.7 mg of zinc per day for nine weeks. (They had a six-week washout period and then switched diets.) The researchers tested the men’s physical performance and found that markers of respiratory and muscle fatigue (peak oxygen uptake, carbon dioxide output and respiratory exchange ratio) were all lower when the men had a lower zinc intake than during the higher zinc phase. Blood tests confirmed that the low-zinc diet reduced the activity of the carbonic anhydrase enzymes in red blood cells. They felt these results might explain poor muscle strength and increased tiredness reported in previous studies on zinc.

Source: Am J Clin Nutr 2005:81(5):1045-1051