BackgroundThe importance of concurrent exercise order for improving endurance and resistance adaptations remains unclear, particularly when sessions are performed a few hours apart. We investigated the effects of concurrent training (in alternate orders, separated by~3 hours) on endurance and resistance training adaptations, compared to resistance-only training. Materials and methodsTwenty-nine healthy, moderately-active men (mean ± SD; age 24.5 ± 4.7 y; body mass 74.9 ± 10.8 kg; height 179.7 ± 6.5 cm) performed either resistance-only training (RT, n = 9), or same-day concurrent training whereby high-intensity interval training was performed either 3 hours before (HIIT+RT, n = 10) or after resistance training (RT+HIIT, n = 10), for 3 d . wk -1 over 9 weeks. Training-induced changes in leg press 1-repetition maximal (1-RM) strength, countermovement jump (CMJ) performance, body composition, peak oxygen uptake ( _ VO 2peak ), aerobic power ( _ W peak ), and lactate threshold ( _ W LT ) were assessed before, and after both 5 and 9 weeks of training. ResultsAfter 9 weeks, all training groups increased leg press 1-RM (~24-28%) and total lean mass (~3-4%), with no clear differences between groups. Both concurrent groups elicited similar small-to-moderate improvements in all markers of aerobic fitness ( _ V O 2peak~8 -9%; _ W LT~1 6-20%; _ W peak~1 4-15%). RT improved CMJ displacement (mean ± SD, 5.3 ± 6.3%), velocity(2.2 ± 2.7%), force (absolute

The aim of this study was to investigate the relationship between mitochondrial content and respiratory function and whole-body insulin resistance in high fat diet (HFD) fed rats. Male Wistar rats were given either a chow diet or a HFD for 12 weeks. After four weeks of the dietary intervention, half of the rats in each group began eight weeks of interval training. In vivo glucose and insulin tolerance were assessed. Mitochondrial respiratory function was assessed in permeabilised soleus and white gastrocnemius (WG) muscles. Mitochondrial content was determined by measurement of citrate synthase (CS) activity and protein expression of components of the electron transport system (ETS). We found HFD rats had impaired glucose and insulin tolerance but increased mitochondrial respiratory function and increased protein expression of components of the ETS. This was accompanied by an increase in CS activity in WG. Exercise training improved glucose and insulin tolerance in the HFD rats. Mitochondrial respiratory function was increased with exercise training in the chow fed animals in soleus muscle. This exercise effect was absent in the HFD animals. In conclusion, exercise training improved insulin resistance in HFD rats, but without changes in mitochondrial respiratory function and content. The lack of an association between mitochondrial characteristics and whole-body insulin resistance was reinforced by the absence of strong correlations between these measures. Our results suggest that improvements in mitochondrial respiratory function and content are not responsible for improvements of whole-body insulin resistance in HFD rats.