Nonlinear analysis is the most suitable method to detect changes in heart autonomic control after exercise of different durations

This study aimed to compare the heart autonomic control (HAC) response during two time-limited physical workouts using linear and nonlinear methods. A total of 20 healthy volunteers performed two physical workouts lasting 5 (P5) and 10 min (P10). In both workouts, volunteers performed as many repetitions as possible within the time limit of sets of 10 repetitions of four different exercises in the order of pull-ups, push-ups, barbell power clean, and barbell shoulder to overhead press. Barbell exercises were performed using a load of 50% of each volunteer's personal record for the jerk lift. Successive RR intervals were recorded 1 h before, immediately after, and 1 h after each workout. HAC parameters were obtained using linear (e.g., time- and frequency-domain analysis) and nonlinear [e.g., recurrence plot (RP)] methods. The number of repetitions was recorded during each workout, and the cadence (e.g., repetitions per minute) was calculated. All HAC parameters showed a significant main effect with time; however, only some RP parameters (e.g., recurrence rate (REC), maximal length of lines (Lmax), and Shannon entropy) were significantly greater in P5. The number of repetitions was significantly greater in P10, but the cadence was higher in P5. Both workouts induced an acute increase in sympathetic activity and vagal withdrawal; however, P5 exhibited greater REC and Lmax, indicating a greater vagal withdrawal. This could be explained by a more intense performance in P5, as evidenced by the greater cadence. In addition, only the RP parameters (a nonlinear approach) were more suitable to detect acute exercise-induced changes in HAC.