Ischemic Preconditioning Did Not Affect Central and Peripheral Factors of Performance Fatigability After Submaximal Isometric Exercise

Abstract

The present study was designed to provide further insight into the mechanistic basis for the improved exercise tolerance following ischemic preconditioning (IPC) by investigating key-determinants of performance and perceived fatigability. Using a randomized, counterbalanced, single-blind, sham-controlled, crossover design, 16 males performed an isometric time-to-exhaustion test with the knee extensors at 20% maximal voluntary torque (MVT) after an IPC and a sham treatment (SHAM). Those who improved their time-to-exhaustion following IPC performed a time-matched IPC trial corresponding to the exercise duration of SHAM (IPC_tm). Neuromuscular function was assessed before and after exercise termination during each condition (IPC, IPC_tm, and SHAM) to analyze the impact of IPC on performance fatigability and its central and peripheral determinants. Muscle oxygenation (SmO₂), muscle activity, and perceptual responses (effort and muscle pain) were recorded during exercise. Performance fatigability as well as its central and peripheral determinants were quantified as percentage pre-post changes in MVT (ΔMVT) as well as voluntary activation (ΔVA) and quadriceps twitch torque evoked by paired electrical stimuli at 100 and 10 Hz (ΔPS100 and ΔPS10⋅PS100^-1 ratio), respectively. Time-to-exhaustion, performance fatigability, its determinants, muscle activity, SmO₂, and perceptual responses during exercise were not different between IPC and SHAM. However, six participants improved their performance by >10% following IPC (299 ± 71 s) compared to SHAM (253 ± 66 s, d = 3.23). The time-matched comparisons (IPC_tm vs. SHAM) indicated that performance fatigability, its determinants, and SmO₂ were not affected, while effort perception seemed to be lower (η_p ² = 0.495) in those who improved their time-to-exhaustion. The longer time-to-exhaustion following IPC seemed to be associated with a lower effort perception (η_p ² = 0.380) and larger impairments in neuromuscular function, i.e., larger ΔMVT, ΔVA, and ΔPS10⋅PS100^-1 ratio (d = 0.71, 1.0, 0.92, respectively). IPC did neither affect exercise tolerance, performance fatigability, as well as its central and peripheral determinants, nor muscle activity, SmO₂, and perceptual responses during submaximal isometric exercise. However, IPC seemed to have an ergogenic effect in a few subjects, which might have resulted from a lower effort perception during exercise. These findings support the assumption that there are 'responders' and 'non-responders' to IPC.

Keywords: central fatigue; contractile function; effort perception; muscle fatigue; muscle pain; pain perception; perceived fatigability; peripheral fatigue.

FIGURE 1

Schematic representation of the experimental design. Participants performed an isometric time-to-exhaustion test with the knee extensors at 20% maximal voluntary torque (MVT) following ischemic preconditioning (IPC) and a sham treatment (SHAM). Those who improved their time-to-exhaustion following IPC were considered as ‘responders’ and performed a time-matched IPC trial corresponding to the SHAM exercise duration (IPC_tm). In case IPC has an ergogenic effect on time-to-exhaustion, this procedure allows a time-matched comparison of neuromuscular data between IPC and SHAM. Electromyography (EMG) and near-infrared spectroscopy (NIRS) data were continuously recorded during exercise. Effort perception and exercise-induced leg muscle pain were recorded every 30 s during exercise.

FIGURE 2

(A) Mean values and individual data of all participants for the time-to-exhaustion tests for the ischemic preconditioning (IPC) and sham (SHAM) condition. (B) Percentage change from pre-exercise values for all participants for maximal voluntary torque (MVT), voluntary activation (VA), twitch torque in response to paired electrical stimuli (PS100), PS10⋅PS100^–1 ratio, and twitch torque in response to a single electrical stimulus (SS). Values are presented as mean ± standard deviation.

FIGURE 3

(A) ‘Responders’ mean values and individual data for the time-to-exhaustion tests for the ischemic preconditioning (IPC) and sham (SHAM) condition. (B) IPC vs. SHAM – Percentage change from pre-exercise values of the ‘responders’ for maximal voluntary torque (MVT), voluntary activation (VA), twitch torque in response to paired electrical stimuli (PS100), PS10⋅PS100^–1 ratio, and twitch torque in response to a single electrical stimulus (SS). (C) Time-matched IPC trial (IPC_tm) vs. SHAM – Percentage change from pre-exercise values of the ‘responders’ for MVT, VA, PS100, PS10⋅PS100^–1 ratio, and SS. Values are presented as mean ± standard deviation. ^∗P < 0.001.

FIGURE 4

(A) Percentage changes in normalized muscle activity of the quadriceps muscle (Q RMS⋅M^–1), muscle O₂ saturation of the vastus lateralis (SmO₂), and effort perception during exercise for the whole sample for the ischemic preconditioning (IPC) and sham (SHAM) condition. (B) IPC vs. SHAM – Percentage changes in Q RMS⋅M^–1, SmO₂, and effort perception during exercise of the ‘responders’ for the IPC and SHAM condition. (C) Time-matched IPC trial (IPC_tm) vs. SHAM – Percentage changes in Q RMS⋅M^–1, SmO₂, and effort perception during exercise of the ‘responders’ for the IPC_tm and SHAM condition. Values are presented as mean ± standard deviation.