EEG Measures of Cortical Activity Return to Baseline Within 24 Hours Despite Differential Protocols Emphasizing Force, Power, and Volume

Abstract

PURPOSE: While a clearer image of the physiological process of recovery from physical exertion is emerging, research into the recovery of the central nervous system is still in its infancy. The purpose of this study was to investigate the nature of motor cortical activity and peak force production 24 hours after resistance exercise. METHODS: Four resistance training protocols were chosen based on their differential interaction with force production: high power (6 x 3 squat jumps at 30% of 1RM); high force (6 x 3 squat at 95% of 1RM); high volume (6 x 10 at 80% of their 1RM); and a control day (6 sets of unracking an empty bar). Twenty-four hours after the intervention, subjects returned to perform a peak isometric squat along with corresponding EEG, perceptual, and blood measures. To control for the rate of adaptation, only highly trained male subjects (years of training: 6+/−1 yrs; squat 1RM: 174+/−26 kg; age: 22+/−3 yrs; body mass: 84.76+/−9.86 kg; n = 7) were included in this study. Cortical activity was measured using an Ag-AgCl electrode-cap, a 40-channel monopolar digital amplifier, and an expanded International 10–20 electrode placement. Linked-ears reference, a ground scalp electrode, and eye electrodes were used to account for electrical artifacts (facial contractions). Movement artifacts were removed using a spatial filter. A 32-bit analog-to-digital converter was used to digitize signals at a sampling rate of 1000hz. High and low frequency bandpass was set at DC and 100hz respectively and signals were low-pass filtered at 50hz using an Infinite Impulse Response (IIR) recursive filter set to a roll-off of 12dB/oct. Impedance was maintained at or below 5 Kohms throughout the experimental protocol. Channels possessing gross artifacts were eliminated. DC drift was removed using a 3rd order polynomial trend correction for each channel. Epochs were set from the completion of the previous movement or the movement of the bar off the rack to the completion of the next repetition. Pearson product-moment correlation coefficients were determined for selected pair wise variables. One-way and univariate analyses of variance (ANOVA) with repeated measures and Fisher's LSD post-hocs were used to detect significant mean differences. Significance level in this study was set at a 0.05 alpha level. RESULTS: Peak isometric squat force was equated by 24 hours post-exercise. The grand average movement related cortical potential area under the curve and mean global field power amplitude were also equated between recovery protocols. Despite the differences between each protocol, we were unable to detect statistically significant differences (in either mean amplitude or area under the curve) for global field power during isometric squats at an alpha level of 0.05. Therefore, the primary finding of this investigation was that 24 hours after differing maximal exertion force production protocols, cortical activity and peak force appear to recover to baseline. CONCLUSIONS: In the present study, the cortical findings suggest that the central responses of well-trained men recover from differing domains of resistance exercise within twenty-four hours. Practical Applications: It is possible that the central nervous system recovers quickly from resistance exercise in the well-trained population. Other limitations to physiological recovery, such as performance decrement, soreness, or fatigue, may be attributable to peripheral, rather than central, causes. Primary damage, particularly with eccentric movement, cannot be ignored. In addition, our laboratory has shown that exercise-induced hypoxia results in secondary damage to muscle through a series of biochemical reactions. The role of the central nervous system in the control of physiological function cannot be underestimated, and this study should be placed appropriately within the context of this evolving area of research.