Effects Of A Predominantly Downhill Full-marathon On Knee Extensor Muscle Function

Downhill running (DR) is shown to alter muscle structure and performance as it requires eccentric loading followed by rapid concentric force production. The effects of repetitive eccentric loading on the muscles due to DR have been investigated mostly in controlled settings rather than in actual competition settings. Additionally, relatively few studies have evaluated the effects of completing a marathon past 24 hours, likely due to participant availability. PURPOSE: The purpose of this study was to examine the effects of eccentric loading during DR in a long-distance competition setting on the function of the knee extensor muscles before to 2 days after the race. METHODS: This study used a repeated-measures design to examine the effects of running a predominantly downhill full-marathon on muscle function in 24 runners (12 female; 37.8 ± 10 years of age; 25 miles of mean weekly mileage; 11 years of mean running experience). It was part of a larger research investigating the biomechanical and physiological responses to running a predominantly eccentric marathon. The peak knee extension force (Fmax), rate of force development to Fmax (RFD+), and the rate of force decline from Fmax (RFD-) were determined during 5-second isometric contractions using a force transducer. The measurements were taken in the morning of the race (PRE), immediately after the race at the finish line (POST), and 2 days later (48H). RESULTS: A marathon-distance DR led to a significant reduction in Fmax (PRE 643.8 N; POST 508.4 N; 48H 525.3 N) and RFD+ (PRE 2110.4 N/s; POST 1410.6 N/s; 48H 1450.8 N/s) at POST and 48H compared to PRE. The changes in RFD- were not significant (PRE -37.1 N/s; POST -68.6 N/s; 48H -33.9 N/s). CONCLUSION: The results from this study showed a decrease in Fmax and RFD+ immediately following the race. The Fmax and RFD+ 48H following the race remained significantly below the PRE testing. RFD- was not affected by an endurance DR. Supported by: Ambrose Amos Shaw Endowment Chair Grant