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Fitness/Health

(56) EFFECT OF SEX AND INTENSITY ON MUSCLE OXYGEN SATURATION RESPONSE DURING ISOMETRIC, HANDGRIP HOLDS TO FAILURE

Thursday, July 11, 2024
2:00 PM – 3:30 PM East Coast USA Time
Location: Exhibit Hall
Abstract Details: It has been reported that females tend to be more fatigue resistant than males, particularly at lower intensities (< 50% maximal voluntary isometric contraction [MVIC]), and these differences in fatigability may be related to intramuscular blood flow. Near-infrared spectroscopy (NIRS) has been used to investigate potential alterations in blood flow and muscle oxygen saturation (SmO2) during exercise.

Purpose: This study compared the patterns of SmO2 responses during isometric handgrip holds to failure (HTF) at 30% vs. 60% MVIC in males and females. METHODS: Twelve females (Mean±SD; 22.8±3.8yr, 166.2±5.5cm, 68.0±13.5kg) and twelve males (28.2±3.8yr, 179.2±7.0cm, 82.5±17.5kg) performed isometric handgrip HTFs at 30% and 60% MVIC on separate days. Time to task failure (TTF) was recorded and SmO2 responses were obtained from a NIRS device placed on the flexor digitorum superficialis. The time course of SmO2 response was recorded in standardized segments of 5% TTF yielding 20 time points (5%-100%). 2-way mixed factorial ANOVAs with appropriate follow-up procedures were used to examine the TTF and SmO2 (p£0.05). A prior planned paired samples t-tests for comparisons of each time point, relative to 5% TTF, and for comparisons of each time point between the intensities were performed at an alpha of p£0.01. A priori planned comparisons for sex-differences in the % SmO2 change (initial – final time point) were examined with separate, independent samples t-tests for the 30% and 60% MVIC HTF (p£0.05). RESULTS: For TTF, there was no sex x intensity interaction (p=0.129) or main effect for sex (p=0.117), but TTF for 30% MVIC HTF (181.7±40.7 sec) was greater (p< 0.001) than 60% MVIC HTF (103.4±32.2 sec). For SmO2, there were interactions between sex x time (p=0.016) and time x intensity (p< 0.001). For the women, relative to 5% TTF, there were significant decreases in SmO2 (10-20%, and 100% TTF) for the 30% MVIC HTF and all time points for the 60% MVIC HTF. There was no significant difference (p≥0.01) in SmO2 between the intensities throughout the HTF for the women. For the men, relative to 5% TTF, there were significant decreases (15-45% TTF) for the 30% MVIC HTF and all time points for the 60% MVIC HTF. Moreover, the SmO2 for the 30% MVIC HTF were greater than the 60% MVIC HTF from 55% to 100% TTF. There was no difference in % SmO2 decreases (initial – final time point) between the men (10.7±14.2%) and women (8.5±8.9%) for the 30% MVIC HTF (p=0.315), but the men (34.2±12.7%) showed greater decreases in % SmO2 than the women (18.9±17.2%) for the 60% MVIC HTF (p=0.021). CONCLUSIONS: At a higher intensity, men demonstrated greater muscle oxygen desaturation than women, which may be attributed to differences in muscle fiber type or mitochondrial characteristics between the sexes. Despite the greater SmO2 desaturation in men than women, there were similar TTF between the sexes which may have been influenced by the individual sensory tolerance limit (STL). PRACTICAL APPLICATIONS: A comprehensive perspective (e.g. STL) integrating central and peripheral (e.g. SmO2) fatigue is necessary when identifying the underlying mechanisms of fatigue between the sexes. When prescribing exercise, practitioners should also consider sex and exercise intensity on the relationships between neuro-physiological responses and actual performance.

Acknowledgements: None