Novel eccentrically biased exercise (downhill running) induces unequal strength loss and soreness across the quadriceps muscles, with the vastus lateralis exhibiting greater low-frequency force deficits and soreness than the vastus medialis.
Key Findings
Results
Downhill running produced significant immediate and 2-day reductions in maximal voluntary contraction (MVC) torque in the quadriceps.
Pre-DHR MVC torque was 214.5 ± 19.2 Nm, dropping to 160.2 ± 17.4 Nm immediately post-DHR (P < 0.001).
At 2 days post-DHR, MVC torque remained depressed at 177.1 ± 20.9 Nm (P = 0.002).
Level walking control group showed no significant change in MVC torque (P > 0.769).
The DHR protocol consisted of 60 minutes of downhill treadmill running in 8 male subjects aged 18-35.
Reductions in MVC torque ranged from approximately 17% at 2 days to approximately 25% immediately post-exercise.
Results
The vastus lateralis (VL) exhibited greater low-frequency stimulated torque deficits than the vastus medialis (VM) following downhill running.
VL showed greater 10-Hz-stimulated torque deficits compared to VM (P = 0.028).
Torque was assessed through electrical stimulation of individual quadriceps muscles at 10 Hz and 40 Hz.
Low-frequency force depression (10 Hz) is indicative of excitation-contraction coupling failure, a hallmark of exercise-induced muscle damage.
Measurements were taken before, immediately following, and 2 days after exercise.
Results
The vastus lateralis experienced greater muscle soreness than the other quadriceps muscles, including the vastus medialis, at 2 days post-downhill running.
VL soreness was significantly greater than VM soreness after DHR (P < 0.001).
Soreness of individual quadriceps muscles was assessed before, immediately following, and 2 days after exercise.
These findings indicate differential soreness distribution across the agonist muscle group following eccentrically biased exercise.
Results
Reduced muscle activation and stimulated torque depression accounted for the greatest variability in MVC torque following downhill running.
Reduced muscle activation (EMG RMS during MVCs) accounted for variability in MVC torque with R² = 0.444 (P < 0.001).
Stimulated torque depression at 10 Hz and 40 Hz accounted for R² = 0.253–0.278 of variability in MVC torque (P < 0.01).
These findings suggest both muscular (peripheral) and neural contributions to strength deficits following unaccustomed exercise.
Results
The downhill running group showed greater quadriceps muscle activation (EMG RMS) during level running immediately post-exercise compared to the control group.
The DHR group showed significantly greater quadriceps muscle activation during level running than the control group immediately postexercise (P < 0.001).
EMG RMS was measured during level running as well as during MVCs.
Increased activation during running post-DHR suggests compensatory neural recruitment to maintain locomotor output despite muscle damage.
This contrasts with reduced muscle activation observed during MVCs, indicating a task-dependent neural response.
Methods
The study design involved 15 healthy male subjects randomly assigned to downhill running or level walking control conditions.
Fifteen healthy, sedentary, or recreationally active male subjects aged 18-35 were included.
Eight subjects performed 60 minutes of downhill treadmill running (DHR group); 7 subjects performed 30 minutes of level treadmill walking (control group).
Measurements were taken at three time points: before, immediately following, and 2 days after exercise.
Individual muscle torque was assessed via electrical stimulation, and soreness of individual quadriceps muscles was measured separately.
Discussion
Unaccustomed eccentrically biased exercise induces differential muscle damage across individual muscles within an agonist muscle group.
The vastus lateralis showed both greater stimulated torque deficits and greater soreness compared to the vastus medialis.
These findings challenge assumptions that strength loss is uniform across agonist muscle groups following exercise-induced muscle damage.
The authors note this has potential implications for understanding injury risk and rehabilitation targeting specific muscles within a group.
What This Means
This research suggests that when people perform downhill running — a type of exercise that heavily stresses muscles through lengthening contractions — not all muscles in the thigh (quadriceps) are equally affected. In a study of 15 healthy young men, those who ran downhill for 60 minutes experienced a roughly 25% drop in quad strength immediately afterward and remained about 17% weaker two days later. By contrast, a control group that walked on a flat treadmill showed no meaningful strength changes. Importantly, when researchers electrically stimulated individual quad muscles to measure their independent strength, the vastus lateralis (the outer thigh muscle) showed greater weakness and more soreness than the vastus medialis (the inner thigh muscle), suggesting that downhill running damages these muscles to different degrees.
The researchers also found two distinct reasons for the overall strength loss: the muscles themselves became weaker (as shown by reduced response to electrical stimulation, a sign of damage to the cellular machinery that generates force), and the nervous system also sent weaker signals to the muscles during maximum effort contractions. Interestingly, during ordinary level running right after the downhill bout, the nervous system actually increased its signals to the quad muscles — possibly to compensate for their reduced capacity and maintain normal movement.
This research suggests that exercise-induced muscle damage does not affect all muscles within a group equally, which has potential relevance for understanding why certain muscles may be more prone to injury or slower to recover after demanding physical activity. The finding that the vastus lateralis is disproportionately stressed by downhill running could be useful context for sports science, physical therapy, and exercise program design, though further research would be needed to explore practical applications.
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Rawdon C, Ingalls C, Yang F, Otis J, Brandenberger K, Jackson M, et al.. (2026). Downhill running differentially reduces stimulated contraction torque in human quadriceps muscles.. Journal of applied physiology (Bethesda, Md. : 1985). https://doi.org/10.1152/japplphysiol.00765.2025