# Interplay Among Muscle Oxygen Saturation, Activation, and Power on a Swim-Bench

## TL;DR

This study examines how muscle oxygen saturation, electrical activation, and power output interact during swimming exercises using oximeters and sEMG.

## Contribution

The study is the first to combine oximeters and sEMG during swimming exercises with mechanical power output analysis.

## Key findings

- Both SmO2 and sEMG signals increased significantly with higher mechanical power during the incremental test.
- sEMG detected muscle fatigue through changes in spectral indexes, while no such correlation was found with SmO2.
- Strong correlations were observed between mechanical power and SmO2, as well as between mechanical power and sEMG amplitude.

## Abstract

Muscle activity during exercise is typically assessed using oximeters, to evaluate local oxygen saturation (SmO2), or surface electromyography (sEMG), to analyze electrical activation. Despite the importance of combining these analyses, no study has evaluated both of them during specific swimming exercises in combination with mechanical power output. This study aimed to assess muscle activity during an incremental test on a swim-bench utilizing oximeters and sEMG. Nine male swimmers performed a five-steps test: PRE (3 min at rest), STEP 1, 2, and 3 (swimming at a frequency of 25, 30, and 40 cycle/min for a duration of 2, 2, and 1 min, respectively), and POST (5 min at rest). Each swimmer wore two oximeters and sEMG, one for each triceps brachii. Stroke frequency and arm mechanical power (from ~13 to ~52 watts) estimated by the swim-bench were different among all steps, while no differences between arms were found. SmO2 (from ~70% to ~60%) and sEMG signals (from ~20 to ~65% in signal amplitude) showed a significant increase among all steps. In both arms, a large/very large correlation was found between mechanical power and SmO2 (r < −0.634), mechanical power and sEMG onset/amplitude (r > 0.581), and SmO2 and sEMG amplitude (r > 0.508). No correlations were found between the slope of the sEMG spectral indexes and the slope of SmO2; only sEMG detected electrical manifestation of muscle fatigue through the steps (p < 0.05). Increased muscle activity, assessed by both oximeters and sEMG, was found at mechanical power increases, revealing both devices can detect effort variation during exercise. However, only sEMG seems to detect peripheral manifestations of fatigue in dynamic conditions.