A Randomized Crossover Trial on Acute Stress-Related Physiological Responses to Mountain Hiking
BACKGROUND Single bouts of muscle damaging eccentric exercise (EE) affect glucose metabolism negatively while single bouts of concentric (CE) and not muscle damaging eccentric exercise have positive acute short-term effects on glucose metabolism. It has been proposed that long-term endurance EE might be more effective in improving glucose metabolism than long-term CE when adjusted for energy expenditure. This would imply that adaptations of glucose metabolism are dependent on the type of exercise. Interleukin-6 (IL-6) released from the exercising muscles may be involved in and could therefore explain acute adaptations on glucose metabolism. The aim of the study was to investigate the effects of a single bout of CE and a single bout of EE inducing no or just mild muscle damage, matched for energy expenditure, on glucose metabolism. METHODS 7 healthy but sedentary female participants (age 20.7 ± 2.9 years; BMI 22.45 ± 1.66 kg m(-2); VO2peak 39.0 ± 4.5 ml kg(-1) min(-1)) took part in a randomized cross over trial consisting of 1 h uphill (CE) respectively downhill (EE) walking on a treadmill. Venous blood samples were drawn before, directly after and 24 h after exercise. An oral glucose tolerance test (OGTT) was performed before and 24 h after exercise. RESULTS CE and EE lead to comparable changes of glucose tolerance (area under the curve of the OGTT) (-16.0 ± 25.81 vs. -6.3 ± 45.26 mg dl(-1) h(-1), p = 1.000) and HOMA insulin resistance (-0.16 ± 1.53 vs. -0.08 ± 0.75, p = 0.753). Compared to baseline, IL-6 concentration increased significantly immediately after EE (1.07 ± 0.67 vs. 1.32 ± 0.60 pg ml(-1), p = 0.028) and tended to increase immediately after CE (0.75 ± 0.29 vs. 1.03 ± 0.21 pg ml(-1), p = 0.058). TNF-α concentration decreased significantly immediately after EE (1.47 ± 0.19 vs. 1.06 ± 0.29 pg ml(-1), p = 0.046) but not after CE (1.27 ± 0.43 vs. 1.24 ± 0.43 pg ml(-1), p = 0.686) compared to baseline. CONCLUSIONS Acute effects of a single bout of exercise inducing no or just mild muscle damage on glucose tolerance and insulin resistance seem to be primarily energy expenditure dependent whereas acute anti-inflammatory activity induced by a single bout of exercise appears to be rather exercise type dependent. TRIAL REGISTRATION NCT01890876, clinicaltrials.gov, https://clinicaltrials.gov/.