Leg Dominance Does Not Influence Maximal Force, Force Steadiness, or Motor Unit Discharge Characteristics

Petrović, Ivana; Amiridis, Ioannis G.; Holobar, Aleš; Trypidakis, Georgios; Kellis, Eleftherios; Enoka, Roger M.

doi:10.1249/mss.0000000000002921

“…Finally, our results revealed a slight but significant increase in peak force when the ankle was secured at a joint angle of 90° compared to 130° position (∼8.7%). This increase could be attributed, at least in part, to sarcomere overlengthening beyond the optimal overlap (Bigland‐Ritchie et al., 1992; Petrovic et al., 2022).…”

Section: Discussionmentioning

confidence: 99%

Muscle contractile properties directly influence shared synaptic inputs to spinal motor neurons

Cabral,

Inglis,

Cudicio

et al. 2024

The Journal of Physiology

2

0

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Alpha band oscillations in shared synaptic inputs to the alpha motor neuron pool can be considered an involuntary source of noise that hinders precise voluntary force production. This study investigated the impact of changing muscle length on the shared synaptic oscillations to spinal motor neurons, particularly in the physiological tremor band. Fourteen healthy individuals performed low‐level dorsiflexion contractions at ankle joint angles of 90° and 130°, while high‐density surface electromyography (HDsEMG) was recorded from the tibialis anterior (TA). We decomposed the HDsEMG into motor units spike trains and calculated the motor units’ coherence within the delta (1–5 Hz), alpha (5–15 Hz), and beta (15–35 Hz) bands. Additionally, force steadiness and force spectral power within the tremor band were quantified. Results showed no significant differences in force steadiness between 90° and 130°. In contrast, alpha band oscillations in both synaptic inputs and force output decreased as the length of the TA was moved from shorter (90°) to longer (130°), with no changes in delta and beta bands. In a second set of experiments (10 participants), evoked twitches were recorded with the ankle joint at 90° and 130°, revealing longer twitch durations in the longer TA muscle length condition compared to the shorter. These experimental results, supported by a simple computational simulation, suggest that increasing muscle length enhances the muscle's low‐pass filtering properties, influencing the oscillations generated by the Ia afferent feedback loop. Therefore, this study provides valuable insights into the interplay between muscle biomechanics and neural oscillations. imageKey points We investigated whether changes in muscle length, achieved by changing joint position, could influence common synaptic oscillations to spinal motor neurons, particularly in the tremor band (5–15 Hz). Our results demonstrate that changing muscle length from shorter to longer induces reductions in the magnitude of alpha band oscillations in common synaptic inputs. Importantly, these reductions were reflected in the oscillations of muscle force output within the alpha band. Longer twitch durations were observed in the longer muscle length condition compared to the shorter, suggesting that increasing muscle length enhances the muscle's low‐pass filtering properties. Changes in the peripheral contractile properties of motor units due to changes in muscle length significantly influence the transmission of shared synaptic inputs into muscle force output. These findings prove the interplay between muscle mechanics and neural adaptations.

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“…Finally, this study examined only the FDI muscle. A recent study analyzing MUs in the TA muscle reported that no asymmetry of MUs was observed in males (Petrovic et al 2022 ). Since the upper and lower extremities are used differently, it is likely that the motor control mechanisms are also different, but sex differences in other muscles need to be clarified.…”

Section: Discussionmentioning

confidence: 99%

Sex differences in laterality of motor unit firing behavior of the first dorsal interosseous muscle in strength-matched healthy young males and females

Nishikawa,

Watanabe,

Holobar

et al. 2024

Eur J Appl Physiol

4

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Purpose The purpose of this study was to compare laterality in motor unit firing behavior between females and males. Methods Twenty-seven subjects (14 females) were recruited for this study. The participants performed ramp up and hold isometric index finger abduction at 10, 30, and 60% of their maximum voluntary contraction (MVC). High-density surface electromyography (HD-sEMG) signals were recorded in the first dorsal interosseous (FDI) muscle and decomposed into individual motor unit (MU) firing behavior using a convolution blind source separation method. Results In total, 769 MUs were detected (females, n = 318 and males, n = 451). Females had a significantly higher discharge rate than males at each relative torque level (10%: male dominant hand, 13.4 ± 2.7 pps vs. female dominant hand, 16.3 ± 3.4 pps; 30%: male dominant hand, 16.1 ± 3.9 pps vs. female dominant hand, 20.0 ± 5.0 pps; and 60%: male dominant hand, 19.3 ± 3.8 vs. female dominant hand, 25.3 ± 4.8 pps; p < 0.0001). The recruitment threshold was also significantly higher in females than in males at 30 and 60% MVC. Furthermore, males exhibited asymmetrical discharge rates at 30 and 60% MVC and recruitment thresholds at 30 and 60% MVC, whereas no asymmetry was observed in females. Conclusion In the FDI muscle, compared to males, females exhibited different neuromuscular strategies with higher discharge rates and recruitment thresholds and no asymmetrical MU firing behavior. Notably, the findings that sex differences in neuromuscular activity also occur in healthy individuals provide important information for understanding the pathogenesis of various diseases.

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“…Our results revealed that when the ankle was secured at a joint angle of 90°, peak torque significantly increased compared to the 130° position (∼8.7%). The lower MVC values at 130° could be explained, at least in part, by sarcomere overlengthening beyond the optimal overlap (Bigland-Ritchie et al, 1992, Petrovic et al, 2022). Interestingly, in the current study there were no significant differences in torque steadiness between the 90° or 130° ankle joint positions.…”

Section: Discussionmentioning

confidence: 99%

Muscle contractile properties directly influence shared synaptic inputs to spinal motor neurons

Cabral,

Inglis,

Cudicio

et al. 2023

Preprint

0

View full text Add to dashboard Cite

Alpha band oscillations in shared synaptic inputs to the alpha motor neuron pool can be considered an involuntary source of noise that hinders precise voluntary force production. This study investigated the impact of altering muscle length on the shared synaptic oscillations to spinal motor neurons, particularly in the physiological tremor band. Fourteen healthy individuals performed low-level dorsiflexion contractions at ankle joint angles of 90° and 130°, while high-density surface electromyography (HD-sEMG) was recorded from the tibialis anterior (TA). We decomposed the HDsEMG into motor units spike trains and calculated the motor units’ coherence within the delta (1-5 Hz), alpha (5-15 Hz) and beta (15-35 Hz) bands. Additionally, torque steadiness and torque spectral power within the tremor band was quantified. Results showed no significant differences in torque steadiness between 90° and 130°. In contrast, alpha band oscillations in both synaptic inputs and force output decreased as the length of the TA was moved from shorter (90°) to longer (130°), with no changes in delta and beta bands. In a second set of experiments, evoked twitches were recorded with the ankle joint at 70° and 130°, revealing longer twitch durations in the longer muscle lengthen condition compared to the shorter. These experimental results, supported by a simple computational simulation, suggest that increasing muscle length enhances the muscle’s low-pass filtering properties, influencing the oscillations generated by the Ia afferent feedback loop. Therefore, this study provides valuable insights into the interplay between muscle biomechanics and neural oscillations.

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Leg Dominance Does Not Influence Maximal Force, Force Steadiness, or Motor Unit Discharge Characteristics

Cited by 13 publications

References 47 publications

Muscle contractile properties directly influence shared synaptic inputs to spinal motor neurons

Muscle contractile properties directly influence shared synaptic inputs to spinal motor neurons

Sex differences in laterality of motor unit firing behavior of the first dorsal interosseous muscle in strength-matched healthy young males and females

Muscle contractile properties directly influence shared synaptic inputs to spinal motor neurons

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