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

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.

Keywords: agreement; concurrent validity; incremental workload; oximeter; peripheral fatigue; sEMG.

Figure A1

Agreement between MOXY and NIMO data. Bland–Altman plot representing the mean difference (black line) and ± 1.96 × SD (dash lines) considering the total data. Details of agreement between oximeters in each section (PRE, STEP 1, STEP 2, STEP 3, and POST) are available in the Supplementary Materials.

Figure 1

Mechanical power output (black bars), sEMG amplitude signal (blue), and oxygen saturation signal (orange) of the right triceps brachii during the incremental step test. Data refer to a representative swimmer.

Figure 2

Mean stroke frequency (A) and mean mechanical power (B,C) of each arm in STEP 1, 2, and 3 during the incremental step test at the swim-bench. a b c difference between STEP 1, 2, and 3, respectively. No differences between left and right arms were found.

Figure 3

Mean muscle oxygen saturation (SmO₂) of right and left triceps brachii estimated by oximeters during incremental step test. a, b, c, d, e difference between PRE, STEP 1, 2, 3, and POST, respectively.

Figure 4

Average of onset (A), amplitude (B), mean (C), and median (D) frequency of the sEMG signal of the triceps brachii during STEP 1, 2, and 3 during the incremental test at the swim-bench. * difference between left/right arm; a b c significant difference between STEP 1, 2, and 3, respectively.

Figure 5

Slope of median frequency (a,b), slope of mean frequency (c,d), and slope of SmO₂ (e,f) are shown for both arms. STEP 1 is represented in green, STEP 2 is represented in blue, and STEP 3 is represented in red. The continuous line shows the mean slope of the participants in the respective step, while the shade represents the standard deviation. Intercept values with the y-axis of the regression line were set to 100%.