Influence of time-of-day-specific same-session combined endurance and strength training on maximal and submaximal endurance parameters

Endurance and strength training are often performed concurrently by both elite athletes and recreational individuals. The question of whether the order of exercises or training at certain daytimes yields to different adaptations in endurance and strength parameters, when endurance and strength training are combined into a single training session, has received limited scientific attention. Moreover, effects on cardiorespiratory and neuromuscular variables after same-session concurrent training have shown conflicting results, particularly regarding exercise sequence or time-of-day characteristics. The purpose of the present study was to examine the effect of time-of-day-specific same- session combined endurance and strength training on maximal and submaximal endurance parameters. 52 previously physically active men (age 18-40) completed the study that consisted of a progressive 24-week same-session endurance and strength training program. Subjects were assigned into one of the four training groups: morning training groups performing endurance training before strength training in the same session (mE+S) or performing the opposite training order (mS+E) and evening training groups performing either one of the training sequences (eE+S or eS+E). A fifth group served as a control group (CON) that continued their habitual physical activity. Morning and evening measurements for endurance (maximal graded cycling test) and strength (dynamic leg press) performance were carried out at the beginning, at week 12 and after the intervention at week 24. The primary results showed significant increases in endurance and strength parameters throughout the 24-week intervention period in maximal oxygen consumption (morning measurements: mE+S, mS+E p<0.01; eE+S p<0.001; eS+E p<0.05; at evening: mE+S, mS+E p<0.05; eE+S p<0.01) except for eS+E at the evening tests (p=0.239) and in maximal work rate (at morning: mE+S, eE+S p<0.001; mS+E, eS+E p<0.01; at evening: p<0.001). Significant between-group differences in endurance performance were reported in morning tests between eE+S vs. eS+E (VO2max: 13.3% vs. 4.3%, p<0.05; Wmax: 23.9% vs. 13.7%, p<0.05) and when sorted by training order E+S vs. S+E (VO2max: 12.1% vs. 5.7%, p<0.05; Wmax: 22.0% vs. 15.9%, p<0.05). Dynamic 1RM leg press increased significantly throughout the intervention (at morning and evening tests: mE+S, eE+S, eS+E p<0.001; mS+E p<0.01). In conclusion, this study demonstrated that 24 weeks of time-of-day specific same- session combined endurance and strength training led to significant improvements both in endurance and strength variables. Training sequence influenced positively endurance performance when endurance training preceded strength training. Time-of-day effects and preferable training times for endurance improvements were not confirmed by our findings.