ECSS Paris 2023: OP-BM08
INTRODUCTION: Sense of position (SoP), one component of proprioception, is assessed with joint position reproduction (JPR) tests consisting of reproducing a reference joint position with the ipsilateral or contralateral limb. Previous research indicates divergent age effect on SoP, with studies revealing an inverted U-shaped curve in SoP acuity from childhood to senescence, and others reporting no age effect (1,2,3). These divergent results could partially reflect the variety of JPR protocols (ipsi vs. contralateral, amplitude, direction). This study investigated the effect of age on ankle SoP during ipsi (IPSI) and contralateral (CONTR) JPR tests with two amplitudes in dorsiflexion and one in plantarflexion direction. METHODS: One hundred sixty individuals (3-92 yr) were distributed into 6 groups: Before-Puberty (BP; 3–14 yr), After-Puberty (AP; 14–17 yr), both groups determined based on a maturity test, Young (Y; 20–39 yr), Middle-aged (M; 40–59 yr), Young-Old (YO; 60–75 yrs) and Old-Old (OO; >76 yr) adults. The IPSI test consisted of reproducing a predetermined target ankle position with the same limb, passively presented to the participant for a few seconds (passive-active modality). The CONTR test consisted of reproducing with one limb a target ankle position passively-hold by the contralateral limb (passive-active). Both IPSI and CONTR were performed blind-folded, to a constant dorsiflexion target position (5° dorsiflexion) from 5° (DF10) or 20° (DF25) plantarflexion position (dorsiflexion direction), and to a 10° plantarflexion target position from a 5° (PF15) dorsiflexion position (0°=90° ankle joint; plantarflexion direction). Error was measured as the absolute (absolute error, AE) and the relative (signed error, SE) showling the difference between the target position and the position reproduced by the participant. RESULTS: In IPSI, no significant difference was observed for AE (p>0.05) and SE (p>0.05) between groups, regardless of the direction and amplitude. In CONTR, similar results were obtained for AE (p>0.05) but SE showed that BP group underestimated the target position compared with Y, YO, OO, and YO and OO overestimated the target position compared with M group for DF25 (p<0.001) and DF10 (p<0.001). In contrast, PF15 did not revealed any age difference in SE. CONCLUSION: The lack of age difference in AE suggests that the overall SoP was not influenced by age. However, the differences in SE for dorsiflexion indicates opposite effects between childhood and advancing ages, with children under-estimating and older adults over-estimating the target position compared with young and middle-aged adults. This age effect only observed for CONTR suggests that online processing of proprioceptive inputs from the two limbs changes with age, which may rely on inter-hemispheric transmission of the proprioceptive signal. References 1. Dunn et al. Am J Occup Ther 69, 1-9, 2015 2. Hu et al. Motor Control 27, 596–615, 2023 3. Yang et al. J Sport Health Sci 8, 548–554, 2019
Read CV Anastasia TheodosiadouECSS Paris 2023: OP-BM08
INTRODUCTION: Runners are often confronted with changing external forces. This requires rapid locomotor adjustments, which can be studied using the experimental paradigm of unweighting and reloading. Recently, we found specific adjustments of muscle synergies when running at 60% body weight, compared to 100% body weight (1). In addition to a greater hamstring contribution to the push-off phase, their temporal activations (motor primitives) were wider and more complex. While these adjustments have been described during stable running phases, they need to be specified during the unweighting and reloading transition phases to better understand how locomotor control reorganizes at each running cycle. METHODS: Thirty-eight men (19±1 yrs) ran sequentially on a lower body positive pressure treadmill at 100, 60 and 100% body weight. The analysis focused on the unweighting and reloading transitions (18±3 and 16±2 running cycles, respectively). Each running cycle was normalized to 200 points (100 points for both stance and flight phases). Muscle synergies were extracted from the EMG signals of 11 right lower limb muscles using non-negative matrix factorisation, and divided into motor modules and motor primitives. Linear mixed models were used to test the adjustments of their Centre of Activity (CoA), Full Width at Half Maximum (FWHM) and Higuchi’s Fractal Dimension (HFD) during both transition types, which were each divided into 8 slides of 5% body weight reduction (from S1: [100-95%] to S8: [65-60% body weight]). RESULTS: The CoA of the push-off motor primitives increased significantly from S4 during the unweighting transition (ES=1.1, p<.001), whereas it decreased significantly from S6 during the reloading transition (ES=0.8, p<.01). Regardless of transition type, the CoA of the late flight primitives decreased from S7 (ES=1.2, p<.05). Regardless of the slide, the CoA of the braking primitives and the FWHM of the push-off primitives were higher during the unweighting transition than during the reloading transition (+33±11%, ES=0.3, p<0.01 and +9±3%, ES=0.4, p<.001, respectively). The HFD of the braking primitives was lower during the unweighting transition than during the reloading transition (-0.8±0.3%, ES=0.3, p<.01). CONCLUSION: During the unweighting transition, the push-off motor primitives shifted later and the late flight primitives shifted earlier in the running cycle. The latter result is attributed to the gradual increase in the contribution of the hamstring muscles to the push-off phase, previously reported at 60% body weight (1,2). Finally, the stance motor primitives were wider and of lower complexity during the unweighting transition than during the reloading transition. As both are indicators of perturbed locomotion (3), the unweighting transition may require a more robust locomotor control due to the unusual sensory and temporal constraints on the musculoskeletal system. (1) Fazzari et al., Sci Reports, 2024 (2) Fazzari et al., Front Physiol, 2023 (3) Santuz et al., iScience, 2020
Read CV Camille FazzariECSS Paris 2023: OP-BM08
INTRODUCTION: Perturbation-based exercise interventions can improve muscle strength and reduce low back pain intensity (1,2). It is suggested that the exposure to perturbations leads to an increase in muscle activation and specific modulations in motor control which improve the ability of the sensorimotor system to cope with perturbations. However, there is a lack of experimental data to support this assumption. Therefore, the current study aimed to investigate the effects of perturbations on muscle activation and modular organization of trunk and leg muscles during a functional exercise. METHODS: Twenty healthy participants (height 175.96 ± 9.27 cm, body mass 71.89 ± 13.25 kg, age 29.55 ± 7.21 years) performed a series of loaded back squats under four different conditions. The loaded back squats were either unperturbed (NP), perturbed unilateral using unstable ground (UGP) or unstable load (ULP) or perturbed bilateral (BP) combining unstable ground and load. Ground reaction forces, joint kinematics, and the electromyographic (EMG) activity of 14 trunk and leg muscles (bilateral) were recorded. We extracted muscle synergies using non-negative matrix factorization and analyzed the data with statistical parametric mapping and linear mixed models. RESULTS: Perturbations significantly (p<0.05) increased the velocity of the center of pressure (CoP) with concomitant adjustments in ankle-, knee- and hip-joint kinematics. When compared to NP, the EMG activity of most leg muscles was significantly increased (p<0.05) in BP and UGP, while most trunk muscles showed an increased EMG activity (p<0.05) in BP and ULP. Four fundamental synergies were detected among all conditions. However, we found alterations within the basic activation patterns of the muscle synergies due to the perturbed conditions. In two synergies the full width at half maximum (FWHM) of the temporal components was significantly (p<0.05) reduced during the perturbed conditions, while in one synergy the center of activation (CoA) was shifted towards an earlier time point (p<0.05). CONCLUSION: The higher muscle activation and CoP velocity indicate an enhanced demand for the sensorimotor system to perceive sensory signals and to generate appropriate motor commands during the perturbed back squats. The recruitment of the same number of muscle synergies in both perturbed and unperturbed conditions indicate a robust neuromotor control during loaded back squats. However, the adjustments in the temporal structure (i.e. changes in FWHM and recruitment time) of the muscle synergies during the perturbed back squats may facilitate the ability of the sensorimotor system to deal with perturbations and may contribute to the reported effectiveness of perturbation-based exercise interventions on the therapy and prevention of low back pain (1,2). REFERENCES: (1) Arampatzis et al., Eur J Appl Physiol, 2107 (2) Arampatzis et al., Transl Sports Med, 2020
Read CV Lukas HauserECSS Paris 2023: OP-BM08