Investigation of the relationship between fatigue levels with motor unit size index and varying neural adaptation depending on different training protocols

Objective: The aim of this study was to investigate the correlation between strength and HIIT training-induced changing neural adaptation and motor unit size index with fatigue levels. Method: 62 healthy male participants aged 18-30 years were included to the study. The participants were randomly divided into three groups as Strength Training Group (n=23), HIIT Training Group (n=21) and Control Group (n=18). Training groups participated in the training program 3 days a week, at least 20 min. up to 60 min. training per day for 8 weeks. The control group did not participate in any training protocol. All participants were measured height and weight, Hoffmann Reflex, Recurrent Inhibition, Presynaptic Inhibition, Fatigue measurement with superficial EMG, isokinetic strength, isokinetic endurance and MUNIX before and after 8 weeks of training. Variance Analysis (ANOVA) in Repeated Measures was used to examine the change and interaction of each group. In the statistical analysis, Post-Hoc Bonferonni correction was used in order to obtain multiple comparisons in the data obtained from group and time differences. Pearson Correlation analysis was used to determine the correlation between variables. Results: It was determined that 8 weeks of HIIT and Strength training increased the isokinetic strength and endurance also motor neuron excitability, recurrent inhibition, presynaptic inhibition and motor unit size index (p <0.01). It was determined that the fatigue index of HIIT and Strength training groups increased (p<0.01). It was determined that there was a significant negative correlation between recurrent inhibition and presynaptic inhibition with fatigue index (p <0.01). It was seen that there was a positive correlation between motor unit size index and Hoffman reflex (p <0.05). There was no statistically significant correlation between fatigue index and motor unit size index (p> 0.05). Conclusion: It can be said that 8 weeks of HIIT and Strength training improved neural adaptation, motor unit size index and fatigue.