Initial Muscle Quality Affects Individual Responsiveness of Interleukin-6 and Creatine Kinase following Acute Eccentric Exercise in Sedentary Obese Older Women

SIMPLE SUMMARY: Muscle health should be prioritized in individuals with conditions who may be at risk of obesity accompanied by sarcopenia. In this context, muscle quality is a novel index of functional capacity that is increasingly relied upon as a critical biomarker of muscle health in low-functioning aging. However, there is scarce evidence regarding which muscle phenotype elicits a more robust effect on important molecules responsible for muscle regeneration and energy homeostasis. Hence, in this study, we evaluated the time-course responses on interleukin-6 and creatine kinase levels following acute eccentric resistance exercise in sedentary obese elderly women with muscle quality differences. This issue is valuable because eccentric exercise may be a particularly promising approach for older adults to efficiently improve muscle mass, strength, and functional performance. We observed that obese older women with high baseline muscle quality display significant increases of interleukin-6 and creatine kinase following an acute eccentric exercise intervention. Such individuals are commonly termed “high-responders”. In contrast, the participants with low muscle quality showed exceptionally small responses (“low responders”) for these molecules compared to individuals with high baseline muscle quality. Muscle phenotype can potentially contribute to individual variation in exercise responses. This phenomenon of responsiveness may clarify important training adaptations. ABSTRACT: This study aimed to evaluate the time course and responsiveness of plasma interleukin-6 (IL-6) and creatine kinase (CK) levels following acute eccentric resistance exercise in sedentary obese older women with a different muscle quality index (MQI). Eighty-eight participants (69.4 ± 6.06 years) completed an acute eccentric resistance exercise (7 sets of 10 repetitions at 110% of 10-repetition maximum with 3 min rest interval). Participants were divided into two groups: high or low MQI according to 50th percentile cut-off. The responsiveness was based on minimal clinical important difference. There were no differences between groups and time on IL-6 and CK levels (p > 0.05). However, the high MQI group displayed a lower proportion of low responders (1 for laboratory and 2 for field-based vs. 5 and 4) and a higher proportion of high responders for IL-6 (7 for laboratory and 6 for field-based vs. 4 and 5) compared to low MQI group. In addition, the high MQI group showed a higher proportion of high responders for CK (11 for laboratory and 9 for field-based vs. 6 and 6) compared to low MQI. A prior MQI screening can provide feedback to understand the magnitude response. Individual responsiveness should be taken into consideration for maximizing eccentric exercise prescription.