Muscle Energetics and The Cardiovascular Response to Isometric Exercise and Post Exercise Circulatory Occlusion Following Exercise-Induced Muscle Damage: Insights from multi-parametric MRI

Fabio Zambolin^1*Jean-Christophe Lagacé²Susan Pinner¹James Mcstravick¹Fiona Smith¹Aneurin J Kennerley¹Jamie McPhee¹

• ¹Department of Sport and Exercise Sciences, Manchester Metropolitan University, Manchester, United Kingdom
• ²Research Centre on Aging, Sherbrooke Geriatric Insititute, Universite de Sherbrooke, Sherbrooke, Canada

Introduction: Skeletal muscles damaged by exercise exhibit disturbed energy metabolism and microvascular function for several days. However, it remains unclear whether these local changes might affect systemic cardiovascular responses to exercise. The present study aimed to investigate whether damaged muscles show changes in muscle energy metabolism and oxygenation that influence the systemic cardiovascular responses to exercise and post exercise circulatory occlusion (PECO). Methods: A novel multi-parametric magnetic resonance imaging (MRI) and spectroscopy approach was applied. Twelve healthy males completed assessments before and 48 hours after 40 minutes of downhill running (20% decline). Assessments included muscle function, inflammation and multi-parametric imaging at rest, exercise and post-exercise occlusion using ³¹P spectroscopy, ¹H and muscle blood oxygen level dependent and 23Na⁺ imaging to assess phosphate metabolism, oxygenation and sodium disturbances. Mean arterial pressure (MAP) and heart rate (HR) were recorded throughout MRI sequences. Results: 48 hours after downhill running, muscle inflammation and Na⁺ disturbance were evident (both p<0.05). Muscle oxygenation was lower, and inorganic phosphates were higher during exercise and PECO compared with baseline (both p<0.05). However, MAP and HR during exercise and PECO remained unchanged at 48 hours compared with baseline. Conclusion: Our multi-parametric MRI approach provides new insights into the local effects of muscle damage on energy metabolism, oxygenation and Na⁺. Despite these local metabolic and microvascular disturbances, the systemic cardiovascular responses as indicated by MAP and HR, remained unchanged. These new findings suggest a dissociation between muscle metabolites, oxygenation, and the cardiovascular response to exercise and PECO 48 hours after damaging exercise.