Biology subjects

Nordez, A.

Publications and source records attributed to Nordez, A..

3 recordsLinked to original sources

bioRxiv2026

Effect of joint velocity and pre-activation on the torque-fascicle length relationship of the vastus lateralis

Fascicle operating length during dynamic tasks is often compared to the isometric torque-length relationship, but there is a lack of evidence regarding the influence of joint velocity on optimal fascicle length. Moreover, there is no consensus in the literature regarding the influence of contraction initiation (pre-activation or passive start), although it could alter the interaction between fascicles and the tendon. This study aimed to investigate the effect of joint velocity and pre-activation on the torque-angle and torque-length relationships of the vastus lateralis during mono-articular isokinetic knee extensions. Twenty-one participants performed isometric, isokinetic (50{degrees}.s-1 to 450{degrees}.s-1), and isokinetic knee extensions with maximal isometric or eccentric pre-activation at 100{degrees}.s-1 and 300{degrees}.s-1. Torque, joint angle, fascicle length, and electromyographic activity of the quadriceps femoris muscles were recorded during contractions and then used to model the torque-angle and torque-length relationships. We were able to successfully fit the torque-angle and torque-length relationships (R{superscript 2}=0.93 and R{superscript 2}=0.92, respectively). A main effect of velocity was detected regarding the optimal angle (p<0.05), but no significant change was observed for the optimal fascicle length. Isometric pre-activation induced a reduction in maximal torque production compared with eccentric pre-activation and passive conditions at both isokinetic velocities (p<0.001), with no change in muscle activity. Our results suggest that muscle-tendon interactions may permit a dissimilar behavior between the torque-angle and the torque-fascicle length relationships. The reduction in torque following isometric pre-activation may be related to a contraction history-dependent phenomenon. NEW & NOTEWORTHYWe demonstrated that, at a given joint angle, increasing velocity altered fascicle operating length without shifting optimal fascicle length, likely because of muscle-tendon interactions. We also showed that maximal isometric pre-activation before a concentric contraction reduced mean and maximal torque during the isokinetic phase compared with eccentric pre-activation or no pre-activation. This effect may be linked to contraction history, since muscle activity did not differ between conditions.

physiology↗

bioRxiv2025

Expert drummers replicate neuromechanical signatures of physiological tremor at extreme movement frequencies.

This study investigates the neuromechanical characteristics associated with expert drummers ability to achieve unilateral ankle oscillation frequencies of up to 10 Hz, surpassing known limits for lower-body movements. Eighteen experienced drummers performed trials at various frequencies, using a protocol combining H-reflex measurement, motion analysis, and electromyography. Our findings closely parallel neuromechanical signatures observed in ankle tremors, with an average movement frequency of 6.3 Hz (SD: 0.5 Hz), and a modulation range of 5.5-7.3 Hz. Oscillatory behavior may result from the interplay between muscle-tendon mechanics and stretch reflex loops. At 6.3 Hz, soleus activation lasts 56.2 ms, shortening by 2.5 ms/Hz (p < 0.001), while tibialis anterior activation lasts 52.7 ms, decreasing by 5.3 ms/Hz (p < 0.001). The latency between ankle dorsiflexion and soleus activation is 48.5 ms at 6.3 Hz, matching the short-latency stretch reflex, and decreases by 11 ms/Hz (p<0.001). Limiting factors for the drummers maximal frequency are soleus and tibialis anterior co-activation, reducing ankle movement, and high levels of activation in hip and back muscles, associated with discomfort and pain. Drummers with higher maximal frequencies (above 7.5 Hz, n = 6) show shorter tibialis anterior activation durations (34.3 ms vs. 53.2 ms, p = 0.0013) and reduced tensor fascia latae activation (6.2% vs. 21.0%, p = 0.0135). These findings highlight phenomenological similarities between the ankle technique and physiological tremors, in terms of neuromechanical timing and oscillatory patterns. Precise tibialis anterior timing and relaxed proximal muscle activation are critical for performance, while injury prevention strategies remain essential. Significance StatementThis study provides a neuromechanical analysis of expert metal drummers producing exceptionally high-frequency ankle movements--up to 10 Hz--that surpass known limits for lower-body movements, and draws parallels with physiological action tremors. By comparing their motor patterns to those reported in tremor literature, this work highlights the role of neuromuscular timing and mechanical adaptations, such as stretch reflex dynamics and muscle-tendon interactions. The findings demonstrate that precise tibialis anterior timing and relaxed proximal muscles are critical for performance, while stabilization demands increase the risk of musculoskeletal disorders in the lower back and hips. These insights bridge performance science, biomechanics, and injury prevention, offering valuable perspectives for optimizing high-frequency movements in music, sports, and rehabilitation.

physiology↗

bioRxiv2022

Handedness is associated with less common input to spinal motor neurons innervating different hand muscles

Whether the neural control of manual behaviours differs between the dominant and non-dominant hand is poorly understood. This study aimed to determine whether the level of common synaptic input to motor neurons innervating the same or different muscles differs between the dominant and the non-dominant hand. Seventeen participants performed two motor tasks with distinct mechanical requirements: an isometric pinch and an isometric rotation of a pinched dial. Each task was performed at 30% of maximum effort and was repeated with the dominant and non-dominant hand. Motor units were identified from two intrinsic (flexor digitorum interosseous and thenar) and one extrinsic muscle (flexor digitorum superficialis) from high-density surface electromyography recordings. Two complementary approaches were used to estimate common synaptic inputs. First, we calculated the coherence between groups of motor neurons from the same and from different muscles. Then, we estimated the common input for all pairs of motor neurons by correlating the low-frequency oscillations of their discharge rate. Both analyses led to the same conclusion, indicating less common synaptic input between motor neurons innervating different muscles in the dominant hand than in the non-dominant hand, which was only observed during the isometric rotation task. No differences in common input were observed between motor neurons of the same muscle. This lower level of common input could confer higher flexibility in the recruitment of motor units, and therefore, in mechanical outputs. Whether this difference between the dominant and non-dominant arm is the cause or the consequence of handedness remains to be determined. Key points- How the neural control of manual behaviours differs between the dominant and non-dominant hand remains poorly understood. - We decoded the spiking activities of spinal motor neurons innervating one extrinsic and two intrinsic hand muscles during isometric tasks. - We estimated the common synaptic input to motor neurons innervating the same or different muscles. - There is less common synaptic input between motor neurons innervating different muscles in the dominant than in the non-dominant hand during isometric rotation tasks. - No differences in common input were observed between motor neurons of the same muscle. - Lower level of common input could confer higher flexibility in the recruitment of motor units.

neuroscience↗