Abstract
Downhill running (DR) is a whole-body exercise model that is used to investigate the physiological consequences of eccentric muscle actions and/or exercise-induced muscle damage (EIMD). In a sporting context, DR sections can be part of running disciplines (off-road and road running) and can accentuate EIMD, leading to a reduction in performance. The purpose of this narrative review is to: (1) better inform on the acute and delayed physiological effects of DR; (2) identify and discuss, using a comprehensive approach, the DR characteristics that affect the physiological responses to DR and their potential interactions; (3) provide the current state of evidence on preventive and in-situ strategies to better adapt to DR. Key findings of this review show that DR may have an impact on exercise performance by altering muscle structure and function due to EIMD. In the majority of studies, EIMD are assessed through isometric maximal voluntary contraction, blood creatine kinase and delayed onset muscle soreness, with DR characteristics (slope, exercise duration, and running speed) acting as the main influencing factors. In previous studies, the median (25th percentile, Q1; 75th percentile, Q3) slope, exercise duration, and running speed were − 12% (− 15%; − 10%), 40 min (30 min; 45 min) and 11.3 km h−1 (9.8 km h−1; 12.9 km h−1), respectively. Regardless of DR characteristics, people the least accustomed to DR generally experienced the most EIMD. There is growing evidence to suggest that preventive strategies that consist of prior exposure to DR are the most effective to better tolerate DR. The effectiveness of in-situ strategies such as lower limb compression garments and specific footwear remains to be confirmed. Our review finally highlights important discrepancies between studies in the assessment of EIMD, DR protocols and populations, which prevent drawing firm conclusions on factors that most influence the response to DR, and adaptive strategies to DR.
Highlights
Eccentric muscle contractions occur when the magnitude of the force applied to the muscle exceeds the strength produced by the muscle itself, resulting in a lengthening action of the musculotendinous system
Evidence is lacking to support the use of in-situ strategies such as compression garments, specific footwear, or modification in running stride to limit muscle damage induced by downhill running (DR), which highlights the need for further high-quality research
DOMS, delayed onset muscle soreness; EIMD, exercise-induced muscle damage; FSP, foot stride pattern; HS, heat stress (30° C); KE, knee extensors; MVC, maximal voluntary contraction; PSF, preferred stride frequency; repeated bout effect’ (RBE), repeat bout effect; RE, running economy; r’, recovery duration; V O2max, maximal aerobic capacity measured on level grade unless otherwise stated; sV O2max, running speed associated with V O2max; +, positive effect; −, negative effect; ↔, no effect
Summary
Due to its eccentric nature, downhill running (DR) induces lower limb muscle damage, manifested by alterations in muscle structure, muscle function, and ensuing running performance for up to several days after exercise. Manipulating DR characteristics (slope, running speed, and duration), independently or not, can influence the extent of exercise-induced muscle damage (EIMD). Trained and/or accustomed people generally experience less muscle damage following DR, it is still unknown if sex and/or age may influence the adaptation to DR. Scientific evidence suggests preventive strategies that consist of prior exposure to DR to limit the extent of muscle damage induced by DR. Evidence is lacking to support the use of in-situ strategies such as compression garments, specific footwear, or modification in running stride to limit muscle damage induced by DR, which highlights the need for further high-quality research
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