Biology subjects

Rozand, V.

Publications and source records attributed to Rozand, V..

4 recordsLinked to original sources

bioRxiv2026

Estimates of persistent inward currents in human spinal motor neurons: non-linear and sex-dependent trajectories from young to very old age

The contribution of persistent inward currents (PICs) to spinal motor neurons discharge rate is lower in old compared to young adults. However, whether this difference further progresses at very old age ([≥]80 years) and differs between males and females remains unknown. Thirty young (26 {+/-} 4 years, 15 females), thirty old (72 {+/-} 5 years, 15 females) and twenty-nine very old adults (85 {+/-} 3 years, 15 females) performed isometric dorsiflexion ramp contractions at 20% of maximal voluntary torque. Individual motor unit spike trains were identified from decomposed high-density surface electromyograms of the tibialis anterior. The paired motor unit technique was used to estimate the prolongation effect of PICs ({Delta}F and normalized {Delta}F), and the quasi-geometric approach to estimate neuromodulatory (brace height) and inhibitory pattern (attenuation slope) contributions. {Delta}F was lower in old and very old adults than in young adults, with no difference between old and very old adults regardless of sex. Compared with young adults, normalized {Delta}F was lower in both old and very old males, whereas in females it is only lower in the very old group. Brace height and attenuation slope did not differ across ages or sexes. These findings indicate that age-related changes in spinal motor neuron excitability are established by the seventh decade and do not progress further in healthy active very old adults, following a nonlinear trajectory that may differ between males and females. The absence of age-related differences in the neuromodulatory index does not support a lower monoaminergic drive in older adults.

physiology↗

bioRxiv2022

Motor imagery training is beneficial for motor memory of upper and lower limb tasks in very old adults

Human aging is associated with a decline in the capacity to memorize recently acquired motor skills. Motor imagery training is a beneficial method to compensate for this deterioration in old adults. It is not yet known whether these beneficial effects are maintained in very old adults (>80 years), more affected by the degeneration processes. The aim of this study was to evaluate the effectiveness of a mental training session of motor imagery on the memorization of new motor skills acquired through physical practice in very old adults. Thirty very old adults performed 3 actual trials of a manual dexterity task (session 1) or a sequential footstep task (session 2) as fast as they could before and after a 20-min motor imagery training (mental-training group) or watching a documentary for 20 min (control group). Performance was improved after 3 actual trials for both tasks and both groups. For the control group, performance decreased in the manual dexterity task after the 20-min break and remained stable in the sequential stepping task. For the mental-training group, performance was maintained in the manual dexterity task after the 20-min motor imagery training and increased in the sequential stepping task. These results extended the benefits of motor imagery training to the very old population, showing that even a short motor imagery training improved their performance and favor the motor memory process. These results confirmed that motor imagery training is an effective method to complement traditional rehabilitation protocols.

neuroscience↗

bioRxiv2022

Wide-pulse electrical stimulation of the quadriceps femoris allows greater maximal evocable torque than conventional stimulation

PurposeThe effectiveness of a neuromuscular electrical stimulation (NMES) program has been shown to be proportional to the maximal evocable torque (MET), which is potentially influenced by pulse characteristics such as duration and frequency. The aim of this study was to compare MET between conventional and wide-pulse NMES at two different frequencies. MethodsMET - expressed as a percentage of maximal voluntary contraction (MVC) torque - and maximal tolerable current intensity (MTCI) were quantified on 71 healthy subjects. The right quadriceps femoris muscle was stimulated with three NMES protocols using different pulse duration/frequency combinations: conventional NMES (0.2 ms/50 Hz; CONV), wide-pulse NMES at 50 Hz (1 ms/50 Hz; WP50) and wide-pulse NMES at 100 Hz (1 ms/100 Hz; WP100). The proportion of subjects reaching the maximal stimulator output (100 mA; MSO) before attaining MTCI was also quantified for each NMES protocol. ResultsThe proportion of subjects attaining MSO was higher for CONV than WP50 and WP100 (30%, 3% and 4%, respectively; p < 0.001). In subjects who did not attain MSO in any protocol, MET was higher for both WP50 and WP100 than for CONV (45% vs 43% vs 39% MVC; p < 0.001). MTCI was lower for both WP50 and WP100 than for CONV (45, 42, and 77 mA, respectively; p < 0.001) and was also lower for WP100 than for WP50. ConclusionWhen compared to conventional NMES, wide-pulse protocols resulted in greater MET, lower MTCI and consequently in a lower proportion of subjects attaining MSO. Overall, this may lead to better NMES training/rehabilitation effectiveness and less practical issues associated with MSO limitations.

physiology↗

bioRxiv2021

Age-related differences in performance and fatigability during an isometric quadriceps intermittent fatigue test

The aim of the present study was to investigate age-related differences in fatigability induced by an isometric quadriceps intermittent fatiguing test in young (<35 years old), old (>60 years old) and very old (>80 years old) men and women. Maximal force loss, contractile function and voluntary activation of the knee extensors were evaluated throughout an isometric fatiguing test using femoral nerve magnetic stimulations. Older adults performed more contractions (index of relative performance) than young (P = 0.046) and very old adults (P = 0.007), without differences between young and very old adults. Total work (absolute performance) was greater for young and old adults compared to very old adults (P < 0.001), without differences between young and old adults. At exhaustion, force loss was greater for young (-28 {+/-} 9%) compared to old adults (-19 {+/-} 8%), but not very old adults (-23 {+/-} 8%). The response to femoral nerve stimulation decreased similarly at exhaustion for the three age groups, indicating similar alteration in contractile function with age. No impairment in voluntary activation was observed. Impairments in neuromuscular parameters were similar for men and women. This study showed that older adults were less fatigable than young adults during an isometric intermittent fatiguing task of the knee extensors. This greater fatigue resistance was not maintained in very old adults independent of sex. Fatigability at exhaustion was likely due to impairments in contractile function for the three age groups.

physiology↗