rectus femoris

Background: Acute dehydration impairs performance, but its effects on resting neuromuscular and tissue mechanics are unclear. We tested whether baseline hydration status and exercise-induced sweat loss alter the resting neuromechanical phenotype of the rectus femoris (RF) as well as skin, subcutaneous tissue (subQ), and fascia overlying the RF. Methods: Thirty physically active men were randomized to hydration guidance (EXP) or habitual intake (CON). Hydration was verified weekly using first-morning urine specific gravity (USG), with targets of USG < 1.018 (EXP) and USG > 1.018 (CON). Participants performed continuous cycling at 50% maximal power output (Wmax) until ~3% body mass loss. Shear-wave elastography quantified tissue shear modulus (kPa), and tensiomyography assessed RF twitch-derived contractile properties (Dm, Tc, Tr) before and immediately after exercise. SWE data were analyzed using mixed design repeated-measures ANOVA; TMG outcomes were analyzed using non-parametric tests. Results: Baseline measures did not differ between groups. No significant group, time, or interaction effects were observed for RF muscle, skin, or subQ shear modulus. In contrast, fascia shear modulus showed a significant time effect, while TMG outcomes did not change significantly from pre- to post-exercise (all p > 0.05). Deep fascia showed a significant main effect of time, with decreased shear modulus post-exercise (F(1, 21) = 5.06, p = 0.035, η2p = 0.194; Δ = 1.25 kPa; d = 0.41; 95% CI [0.04, 0.78]), independent of hydration group. Conclusions: Under moderate-intensity cycling with approximately 3% body mass loss, we did not detect significant hydration-group differences or significant pre–post changes in resting RF twitch-derived contractile properties or in RF muscle, skin, and subQ shear modulus. Fascia shear modulus decreased after exercise irrespective of hydration group. These findings should be interpreted cautiously: the study was underpowered to detect small effects, and the fascial finding emerged from an exploratory, layer-specific analysis without correction for multiple comparisons. It should therefore be regarded as preliminary and hypothesis-generating, requiring confirmation in adequately powered, pre-registered studies.

matched text: “rectus femoris”

Background/Objectives: This study examined whether foot progression angle and stance width modify lower-limb muscle activation during the holding phase of forward lunges in healthy adults. Methods: Thirty-six healthy adults completed five randomized within-participant lunge conditions: standard stance with 0°, 30°, and 60° foot progression angles and narrow and wide stances with a 0° foot progression angle. Surface electromyographic activity was recorded from the rectus femoris, gluteus medius, vastus lateralis, vastus medialis, biceps femoris, and semitendinosus. The central 2 s of each 6 s trial were analyzed and normalized to maximal voluntary contraction. Data were analyzed using repeated-measures analysis of variance with Bonferroni-adjusted pairwise comparisons. Results: Foot progression angle significantly affected rectus femoris, gluteus medius, vastus lateralis, and vastus medialis activation. Rectus femoris and vastus lateralis activation were higher at 60° than at 0° and 30°, vastus medialis activation was higher at 60° than at 30° only, and gluteus medius activation decreased as foot progression angle increased. Stance width significantly affected rectus femoris, gluteus medius, vastus lateralis, and vastus medialis activation. Rectus femoris activation increased with stance width, gluteus medius activation was lower in standard and wide stances than in narrow stance, and vastus lateralis and vastus medialis activation were higher in standard and wide stances than in narrow stance. Biceps femoris and semitendinosus did not differ across conditions. Conclusions: Foot progression angle and stance width modified selected acute lower-limb EMG responses during the holding phase of bodyweight forward lunges.

matched text: “rectus femoris”