# The Impact of a Modality Switch During Isokinetic Leg Extensions on Performance Fatigability and Neuromuscular Patterns of Response

## TL;DR

Switching from bilateral to unilateral leg exercises during training may increase muscle fatigue and metabolic stress without changing neuromuscular activation strategies.

## Contribution

The study reveals that combining bilateral and unilateral exercises may enhance metabolic stress and peripheral fatigue compared to purely bilateral training.

## Key findings

- Bilateral and unilateral muscle actions showed similar neuromuscular activation strategies.
- Incorporating unilateral exercises after bilateral actions increased peripheral fatigue and metabolic stress.
- No significant differences in peak force or EMG amplitude were found between the tested modalities.

## Abstract

What are the main findings?
Bilateral and unilateral muscle actions elicited similar neuromuscular activation strategies.Incorporating unilateral following bilateral muscle actions may potentiate greater metabolic stress.

Bilateral and unilateral muscle actions elicited similar neuromuscular activation strategies.

Incorporating unilateral following bilateral muscle actions may potentiate greater metabolic stress.

What is the implication of the main finding?
Practitioners should consider selecting exercises based on sport-specific needs.Following bilateral with unilateral muscle actions could be a method of eliciting greater muscular adaptations via metabolic stimulation of hypertrophic mechanisms.

Practitioners should consider selecting exercises based on sport-specific needs.

Following bilateral with unilateral muscle actions could be a method of eliciting greater muscular adaptations via metabolic stimulation of hypertrophic mechanisms.

Bilateral (BL) and unilateral (UL) muscle actions are commonly incorporated in training programs to achieve distinct goals, however, the mechanisms driving modality-specific training adaptations remain unclear. This study examined peak force, electromyographic (EMG) amplitude (AMP), and mean power frequency (MPF) of the non-dominant leg during isokinetic leg extensions performed as either a BL or BLUL combined modality. Twelve recreationally trained men (Mean ± SD; age = 20.8 ± 1.7 years; weight = 83.1 ± 15.7 kg; height = 178.2 ± 7.8 cm) attended 2 test visits that included BL and UL maximal isokinetic leg extensions at 180°·s−1 followed by a fatiguing task of either 50 BL or 25 BL followed immediately by 25 UL (BLUL) maximal, isokinetic leg extensions at 180°·s−1, in random order on separate days. The results demonstrated a 33.3% decline in peak force with a concomitant increase in EMG AMP across the fatiguing task, but there were no significant differences between conditions. For EMG MPF, the BLUL condition exhibited a 19.39% decline versus a 10.97% decline in the BL condition. Overall, the present study suggested there were no significant differences in neuromuscular activation strategies between the tested modalities. However, our findings indicated that incorporating UL muscle actions after a BL task may induce a greater degree of peripheral fatigue compared to sustained BL muscle actions. Practitioners might consider implementing UL exercises at the end of a training bout to induce greater metabolic stress.