Muscle Damage, Inflammatory, And Performance Responses To Submaximal, Metabolically-Matched Load Carriage And Non-Weight Bearing Endurance Exercise

Abstract

PURPOSE: Metabolic and mechanical stressors elicited during submaximal load carriage (LC) and non-weight bearing, conventional endurance (CE) exercise differ, potentially influencing patterns of post-exercise muscle damage, inflammation, soreness, and performance. This study characterized muscle damage, inflammation, soreness, and lower-body muscular performance during recovery from submaximal LC and CE. METHODS: Forty adults (mean ± SD, 22 ± 4 y, 80 ± 10 kg, 4.0 ± 0.5 L·min-1) were randomly assigned (n = 20 per group), to perform either a 90 min submaximal, (2.2 ± 0.1 L·m-1) LC (24 ± 3 kg load) or metabolically-matched non-weight bearing (cycle ergometry), CE bout. Muscle damage, inflammation, ratings of soreness (deltoids, gluteus, quadriceps, and gastrocnemius/soleus), and quadriceps isometric and isokinetic peak force (PF), rate of force development (RFD), and total work were measured at baseline, 3, 24, 48, and 72 h post-exercise. RESULTS: Myoglobin (ng/mL) peaked 3 h post-exercise (70 ± 45) and remained elevated 72 h post-exercise (31 ± 10) compared to baseline (27 ± 8; P < 0.05). Overall, mean myoglobin levels were higher (P < 0.05) with LC (43 ± 31) than CE (34 ± 17). Creatine kinase (IU/L) increased similarly 3, 24, and 48 h post-exercise for LC and CE, but remained elevated 72 h post-exercise (327 ± 128) compared to baseline (205 ± 173) for LC only (mode-by-time, P < 0.05). Lactate dehydrogenase increased to a peak 3 h post-exercise and returned to baseline levels by 24 h, regardless of mode (P < 0.05). Post-exercise (24 and 48 h) interleukin-6 and C-reactive protein levels, which increased post-exercise relative to baseline, were 54% and 61% higher, respectively, for CE than LC (mode-by-time, P < 0.05). Post-exercise quadriceps and gastrocnemius/soleus soreness were similar between LC and CE, whereas gluteal soreness was higher for CE than LC, and deltoid soreness was greater for LC than CE (mode-by-time, P < 0.05). Independent of exercise mode, PF at 60°/sec at 24 h and RFD at 48 h decreased 5% and 13% lower (P < 0.05), respectively. No other differences in performance were observed. CONCLUSION: Although muscle damage, inflammatory, and soreness responses to metabolically-matched LC and CE were different, neither submaximal exercise bout produced meaningful decrements in lower-body, maximal muscular performance. Supported by U.S. Army Medical Research and Material Command.