News & Views from the Editor-in-Chief - L. Bruce Gladden
Three papers in this month's journal particularly caught my attention. First, Allen et al. demonstrated that six weeks of endurance exercise training altered the gut microbiota of previously sedentary lean (n = 18) and obese (n = 14) adults, irrespective of changes in diet. These changes were dependent on obesity status and were largely reversed when the participants subsequently reverted to six weeks of sedentary behavior. Importantly, endurance training resulted in an increase in potentially beneficial short-chain fatty acid concentrations and the genes responsible for their production, particularly in lean participants for whom the changes correlated with alterations in body composition, indicating a relationship between the gut microbiota and physiological responses to exercise training. This study is significant in that it represents the first longitudinal human exercise trial designed to determine the independent effects of exercise training on the gut microbiota and microbial metabolites.
Next, Goltz et al. used a novel approach (the replicated crossover design) to examine the reproducibility of perceived appetite (hunger, fullness, satisfaction, prospective food consumption) and appetite hormone (ghrelin, peptide YY) responses to exercise. Fifteen healthy young men completed two, 1-h running trials and two, 1-h resting trials. Measurements were obtained before and after each bout of exercise and rest. The differences between measurements before and after exercise were compared with those before and after rest on the two occasions to quantify the true individual variability of responses. Appetite responses to acute exercise were found to be reproducible although they were greater in some individuals than others. These findings suggest that some people will experience greater changes in appetite than others in response to exercise and the implications of this finding warrant further investigation.
Finally, Chaseling et al. examined whether cold water ingestion improves exercise tolerance of heat-sensitive people with Multiple Sclerosis (MS) in hot environments. The authors found that relative to drinking thermoneutral (37°C) water, participants with MS were able to exercise about 30% longer when drinking 1.5°C water. Intriguingly though, the improved exercise tolerance with cold water ingestion was not accompanied by lower core or skin temperatures, even after accounting for the longer exercise times. Given that "Uhthoff's phenomenon"—the temporary worsening of MS symptoms (e.g., fatigue) with heat exposure—is traditionally believed to occur due to a critical rise in core temperature of about 0.5°C, this latter finding potentially provides new mechanistic insight into the underlying causes of heat intolerance with MS, for example, feedback from cold-afferent thermoreceptors that reside in the abdomen and oral cavity.
L. Bruce Gladden
School of Kinesiology