Combined Strength and Endurance Training: Effect of Training Order and Time-of-Day on Adaptations in Neuromuscular and Cardiorespiratory Performance, Muscle Hypertrophy, Serum Hormone Concentrations and Wellbeing

Abstract

The aim of this study was to assess the daily fluctuations in strength and endurance performance and to examine chronic adaptations to time-of-dayspecific same-session combined strength (S) and endurance (E) training over the 24-week training period in previously untrained men. Participants were assigned to the morning (m) or evening (e) E+S or S+E group (mE+S n=9; mS+E n= 9; eE+S n=12, eS+E n=12) and trained 2-3 d·wk-1 in the respective time-ofday and training order. In the total group of participants, isometric strength and maximal cycling performance were, respectively, 4.5% and 1.5% higher in the evening compared to the morning. Based on the time-of-day of peak isometric strength performance, high morning performance (n=8), high evening performance (n=19) and neutral types (n=45) were identified. This grouping was valid also for endurance performance. Strength and endurance performance increased in the morning and evening in all training groups over the 24-week training period. Isometric force and EMG activity increased more in S+E compared to E+S, when measured in the evening. Maximal cycling performance increased more in E+S compared to S+E. Muscle hypertrophy was similar between the groups after the first 12 weeks, but evening training led to a larger increase over the weeks 13-24. Serum cortisol and testosterone showed a typical diurnal variation and no changes were observed after 24 weeks of timeof- day-specific training. Motivation to participate to the present training program showed a tendency to decrease after prolonged training in the morning hours. Evening training, however, led to worsened perception of time management. These results suggest that strength as well as endurance performance fluctuates over the day, however, the time for peak performance varies between individuals. In adaptations to combined training, the E+S order may potentially inhibit neural adaptations and thereby hinder adaptations in isometric strength performance, whereas in the S+E order the fatigue from the strength session may inhibit adaptations in endurance performance. Therefore, if combined training is performed over prolonged periods of time, training time and order should be selected based on the personal training goals. Keywords: concurrent training, testosterone, cortisol, diurnal rhythms, HRQoL, motivation, time-management