Motor unit properties in response to maximal concentric and eccentric fatiguing tasks are contraction-type specific, with the concentric task characterized by a more rapid decline and recovery of motor unit discharge rate, whereas the eccentric task produced a more gradual reduction in discharge rate with delayed restoration of motoneuron output and prolonged torque deficits during recovery.
Key Findings
Results
Both concentric and eccentric fatiguing tasks caused substantial reductions in motor unit discharge rate from baseline.
Thirteen participants (5 female) performed repeated maximal dorsiflexion contractions to a 50% torque loss threshold
Fine-wire intramuscular electrodes tracked single motor unit activity in the tibialis anterior
Both tasks caused reductions in MUDR of at least 40% from baseline (P ≤ 0.001)
The matched torque-loss endpoint allowed direct comparison between contraction types within the same individuals
Results
Concentric contractions produced a more rapid reduction in motor unit discharge rate compared to eccentric contractions during the fatiguing task.
CON demonstrated a more rapid reduction in MUDR (P ≤ 0.001)
ECC exhibited a more gradual decline in MUDR
The two conditions converged at task failure, reaching similar levels of MUDR reduction
This differential rate of decline indicates contraction-type-specific neural modulation during fatigue
Results
Concentric motor unit discharge rate and torque recovered to baseline by approximately 10 minutes, whereas eccentric recovery was substantially delayed.
CON MUDR returned to baseline by approximately 10 min (P = 0.415, indicating no significant difference from baseline)
ECC MUDR did not return to baseline until approximately 20 min (P = 0.418)
ECC torque deficits persisted for 30 or more minutes (P ≤ 0.001)
CON torque also recovered by approximately 10 min, matching the MUDR recovery timeline
Results
Electrically evoked measures indicated greater muscle slowing during the concentric fatiguing task and more prolonged contractile impairment following the eccentric fatiguing task.
Electrically evoked twitch properties showed greater muscle slowing during CON (P ≤ 0.01)
More prolonged contractile impairment was observed following the ECC fatiguing task (P = 0.033)
These findings are consistent with greater metabolic cost during concentric contractions and greater peripheral damage from eccentric contractions
Prolonged ECC contractile impairment likely reflects disruption of excitation-contraction coupling or structural damage
Results
M-wave amplitude and voluntary activation recovered similarly between concentric and eccentric conditions.
M-wave amplitude recovered without significant differences between conditions (P > 0.05)
Voluntary activation (VA) also recovered similarly between conditions (P > 0.05)
Similar M-wave recovery suggests that sarcolemmal excitability was not differentially affected between contraction types
Similar VA recovery indicates that supraspinal drive was not a primary differentiating factor between conditions during recovery
Results
A dissociation was observed between motor unit discharge rate recovery and torque recovery following the eccentric fatiguing task.
ECC MUDR recovered to baseline by approximately 20 min, but torque deficits persisted for 30 or more minutes (P ≤ 0.001)
This dissociation suggests that peripheral contractile impairment, rather than reduced motoneuron output, was responsible for sustained torque deficits after eccentric fatigue
The authors attributed this to 'differences in metabolic cost and peripheral contractile impairment induced between contraction types'
No equivalent dissociation was observed following the concentric fatiguing task
What This Means
This research suggests that the way our nervous system and muscles respond to fatigue depends heavily on whether muscles are contracting while shortening (concentric) or lengthening (eccentric). In this study, participants repeatedly performed maximal ankle-lifting movements until their force production dropped by 50%, while researchers recorded the firing rates of individual nerve-muscle units (motor units) in the tibialis anterior, the main muscle used for lifting the foot. Both types of contractions caused large drops in how fast motor units fired, but the pattern differed: concentric exercise caused a faster drop in firing rates, while eccentric exercise led to a more gradual decline that only caught up to concentric levels by the point of task failure.
During recovery, the differences were even more striking. After concentric exercise, both motor unit firing rates and force production returned to normal within about 10 minutes. After eccentric exercise, firing rates took about 20 minutes to recover, and force production remained significantly reduced even after 30 minutes. Importantly, measures of muscle membrane function and voluntary drive to the muscle recovered similarly after both types of exercise, pointing to the muscle tissue itself — rather than the brain or nerve signals — as the main reason for the prolonged weakness after eccentric contractions. This is consistent with the well-known phenomenon of delayed-onset muscle soreness and prolonged weakness after downhill walking or other eccentric-heavy activities.
This research suggests that the mechanisms underlying fatigue and recovery are fundamentally different depending on contraction type. The faster firing rate changes during concentric exercise likely reflect greater metabolic stress (the muscle 'burns out' faster chemically), while eccentric exercise causes more lasting structural or mechanical disruption to the muscle fibers themselves. Understanding these distinctions could have practical implications for designing rehabilitation programs, athletic training protocols, or recovery strategies, as eccentric exercise may require substantially longer recovery periods even when the total amount of fatigue experienced during exercise appears matched.
Check Your Own Numbers
Upload your bloodwork. We'll cross-reference your results against this study and 4,700 others.
Basile D, Rice C. (2026). Differential modulation of motor unit properties during maximal concentric and eccentric fatiguing tasks with recovery in the human dorsiflexors.. Journal of applied physiology (Bethesda, Md. : 1985). https://doi.org/10.1152/japplphysiol.00385.2026