(70) Near-infrared Spectroscopy Resaturation Indices Can Differentiate High and Low Muscle Quality: A Pilot Study

Purpose: Near-infrared spectroscopy (NIRS) in combination with a vascular occlusion test (VOT) is a noninvasive assessment to characterize microvascular function and health in skeletal muscle. Echo intensity, determined via ultrasonography, is used to characterize skeletal muscle quality (MQ) by the echogenicity of contractile and noncontractile components. Thus, it may serve as a marker of muscle impairment and disease. However, few studies have examined the sensitivity of NIRS in distinguishing between different levels of muscle qualities. Therefore, the purpose of this investigation was to examine whether differences in NIRS re-saturation metrics could differentiate individuals with high or low muscle quality. Methods: Eight healthy adults (age:26±6yrs, height:177.5±13.1cm, weight:85.1±21.5kg, body fat: 20±6%) completed body composition analysis, ultrasonography, and a NIRS+VOT. Muscle quality was assessed using ultrasonography-derived echo intensity, which was corrected for adipose tissue thickness. NIRS was attached to the vastus lateralis to collect skeletal muscle tissue oxygenation (StO₂). A cuff was placed at the uppermost portion of the thigh and inflated to a supra-systolic pressure of 250 mmHg to induce ischemia. The VOT consisted of 3 min of baseline values, 5 min of ischemia, and 3 min of reperfusion. Re-saturation metrics were defined as the upslope, re-saturation max, and area under the curve (AUC; prolonged hypersaturation). Upslope was calculated as the first 10 seconds of reperfusion, re-saturation max was quantified as the maximum value observed, and AUC was quantified as the sum of all values exceeding baseline. Participants were dichotomized into two groups at the median. Mean differences were assessed with three independent t-tests. To determine potential relations, bivariate analyses were performed between re-saturation metrics and corrected echo intensity. A p< 0.05 was considered significant. Results: Echo intensity was inversely related to upslope (p=0.042; r=-0.725) and hypersaturation AUC (p=0.048; r=-0.711) but not re-saturation max (p=.069; r= -0.670). There were no significant differences between low and high groups for upslope (High: 1.3±0.86 %·s^-1, Low: 1.9±0.38 %·s^-1; p=0.084; d= 1.463), re-saturation max (High:73.4±2.1 A.U., Low: 76.8±2.5 A.U.; p=0.084; d= 1.464), and hypersaturation AUC (High: 1679.5±295.7 %·s^-1, Low: 1471.0±590.6 %·s^-1; p=0.551; d= .446). However, the Bayesian analyses suggested there may be potential differences in upslope (BF₁₀= 1.427) and re-saturation max (BF₁₀=1.429), but likely not hypersaturation AUC (BF₁₀=0.589). Conclusions: Individuals with better MQ tended to exhibit faster upslopes and higher re-saturation max values than those with poorer MQ. Thus, NIRS re-saturation indices might be able to differentiate individuals based on their muscle quality. This may be further supported with additional participants. Our future studies will continue to examine the utility and sensitivity of NIRS assessments. Practical Applications: Strength coaches remain uniquely qualified to develop skeletal muscle for athletic, clinical, and recreational populations. Based on our findings, improved MQ coincides with improved muscle oxygenation in response to various stresses like transient ischemia. Overall, an individual with adequately developed skeletal muscle will likely exhibit superior oxygen-based recovery characteristics and more resilience to strenuous exercise bouts. Acknowledgements: None