Changes In Mental And Physical Energy And Fatigue Have Unique Biomarkers: An Exploratory Study

PURPOSE: Recent evidence suggests subjective feelings of mental and physical energy and fatigue may have unique and overlapping biological correlates. However, the biological reasons for these moods are likely multifactorial and remain largely unexplored. METHODS: Fifteen subjects (6 female, 9 male; 29 ± 9 y; 71 ± 14 kg) completed 90 min of cycling (81% HRmax) in the heat (~33 °C) with (EUH) or without fluid (DEH). Using visual analogue scales, feelings of mental and physical energy (ME and PE) and fatigue (MF and PF) were measured. Capillary blood biomarkers were assessed pre- and post-exercise, while sweat electrolyte concentrations were assessed at multiple sites during the first and last 30-min of each exercise bout. Only 20 pre-post blood comparisons were analyzed due to difficulty in obtaining blood samples. Changes in mood state were calculated, and participants were bifurcated based on directionality of mood. Mann-Whitney U tests were used to assess differences in biomarkers between those who reported an increase or decrease in ME, MF, PE, PF. Benjamin-Hochberg False Detection Rate of 70% was used to correct for multiple analyses. RESULTS: With EU, 5 subjects reported an increase in ME and PE, and decrease in MF, while 4 reported a decrease in PF. After DEH, 5 reported an increase in PE, 4 an increase in ME, 2 a decrease in MF and all subjects reported an increase in PF. Changes in total blood CO2 were significantly different (p = .02) between subjects who reported an increase in ME (Median[range] = -2[-3,0]mM, n = 15) and those who reported a decrease (0[-2, 1]mM, n = 5). Subjects who reported an increase in MF had significantly (p = .04) lower decreases in blood Cl- (3[-2,7] mM, n = 4) compared to those who reported a decrease (6[4,9]mM, n = 15). For PE, subjects who reported an increase had a significantly (p = .04) lower decrease in hemoglobin (0.6[-0.7, 1]g/dl,n = 15) compared to those who reported a decrease (-0.4[-1.7,1]g/dl, n = 5). Sweat electrolyte concentrations were not significantly different between groups. DISCUSSION: Our findings support previous work suggesting changes in blood biomarkers may impact feelings of ME, MF and PE. Due to the small sample size, we were unable to elucidate the interaction effects. Future studies examining the role of select blood biomarkers on feelings of energy and fatigue are warranted.