4. Discussion
loss of fat-free or skeletal muscle mass, appendicular skeletal muscle mass
RECRUITMENT
The present study indicates that, when combined with four weeks of structured resistance training, TRE is as effective as a habitual dietary pattern in decreasing fat mass while preserving fat-free and appendicular skeletal muscle mass in trained young males. Despite this, the effects of both interventions on upper and lower body strength were different. While after training, the habitual diet condition was compatible with a slightly greater dynamic high-speed strength performance in the lower body, this was not the case for upper body exercise. In fact, improvements in ballistic bench press performance were only seen after four weeks of TRE. In addition, these data also show that both interventions were similarly effective for improving explosive muscle strength in response to isometric upper limb MVC. Despite this, it should be noted that the magnitude of change in the maximum RFD obtained during isometric upper body MVC was greater under the non-TRE condition. Taken together, this study provides preliminary evidence that, when combined with structured resistance training, TRE might potentiate performance in dynamic tasks involving upper body high-speed strength, but this does not occur at the lower body level.According to the current findings, both conditions were similarly effective in decreasing fat mass, without a parallel loss of fat-free or skeletal muscle mass. Specific biological mechanisms have been advocated to explain the effects of TRE on fat mass reduction (e.g., increased mitochondrial biogenesis, enhanced secretion of adiponectin, noradrenaline and growth hormone) [It was observed that neither intervention was effective for improving peak or explosive force in response to isometric mid-thigh pull after training. This is in line with certain past studies showing that, due to its specificity, dynamic resistance training has no impact on improving isometric strength performance [Similar to the case of the countermovement jump, no differences between conditions were observed for the peak force of the squat jump before training. Again, after four weeks of intervention, the combination of resistance training and a habitual dietary pattern resulted in a greater peak force in the squat jump (~6%). The magnitude of this difference is greater than the coefficient of variation reported for this specific variable (~4.3%) [Upper body isometric strength performance was similar between conditions before training. In contrast, after four weeks of intervention, there were greater values in terms of peak RFD (obtained during MVC) under the condition combining resistance training and a habitual dietary pattern (~9%). An elevated peak RFD enables enhanced force production during rapid movements, and this is important for both athletic as well as nonathletic populations [In contrast to the results obtained for peak RFD, there were significant improvements, from pre- to post-training, in explosive force production from 100 to 200 ms in terms of bench press isometric MVC under both conditions. This indicates that qualitative changes may have occurred with resistance training, potentially involving alterations in motoneuron recruitment, rate coding, discharge doublets, myosin heavy chain isoform expression and sarcoplasmic reticulum calcium kinetics [Both conditions were compatible with similar values in terms of upper body high-speed strength performance at pre-training. Yet, while the combination of resistance training with a habitual dietary pattern resulted in a significant reduction (−15%) in peak force in response to the bench press throw exercise after training, this was not seen with TRE. The magnitude of reduction in this specific variable following the intervention involving a habitual dietary pattern was greater than its coefficient of variation (~9.3%). Hence, while TRE induced a slight increase in upper body high-speed strength performance over time, the combination of resistance training with a habitual dietary pattern resulted in its decrease after four weeks of intervention. This finding agrees with isolated scientific data involving the interaction of certain resistance training regimens and high-speed strength performance [