Effects of lower-limb extensors' neuromuscular fatigue on the regularity of running movements: a crossover study.

Neuromuscular fatigue (NMF) reduces the musculoskeletal system's ability to produce force during activities like running. Analysis of motor behaviour's regularity may identify motor system deficits caused by fatigue. The present study investigated whether the NMF of lower limb extensors alters the regularity of running movement and whether this possible effect remains over time. Crossover study with two randomised conditions: NMF and control. Twelve healthy young males participated in this study. Hip, knee, and ankle angles (sagittal plane) and centre of mass (CoM) linear accelerations were assessed during treadmill running at self-selected speed in four assessment conditions: Baseline (pre-NMF), and after NMF (NMF condition) or after rest (control), at the 1st (Time_1), 10th (Time_10) and 20th (Time_20) minutes. Kinematics regularity was measured as Sample Entropy. Repeated measures ANOVAs were used (α = 0.05). NMF reduced regularity of lower limb joints during running, and these effects remained up to 20 minutes. No changes were observed in the CoM accelerations' regularity. The regularity reductions may be an adaptive solution for the motor system to maintain the task performance. The measure of regularity of the lower limb joints' motion is sensitive to NMF and can identify states with deficits in muscles' force production capacity in running.

Effect of sleep deprivation on postural control and dynamic stability in healthy young adults.

BACKGROUND: Postural control results from non-linear interactions of multiple neuromusculoskeletal elements and contextual factors. The use of non-linear analyses that consider the temporal evolution of postural adjustments, such as sample entropy, could inform about the changes in postural control due to contextual disturbances such as sleep deprivation. RESEARCH QUESTION: What are the effects of sleep deprivation on static postural control and dynamic stability in healthy young adults? METHODS: A quasi-experimental study was performed with 17 healthy young males submitted to 24 h of monitored sleep deprivation. The postural control was measured using sample entropy, area, and total average velocity of the center of pressure on a force platform. The dynamic stability was measured using the Modified Star Excursion Balance Test (SEBTm) composite score for each lower limb. Repeated-measures analysis of variance (baseline × 12 h × 15 h × 18 h × 21 h × 24 h of sleep deprivation) verified the effect of sleep deprivation in the postural control variables. Paired t-test compared the composite score of the SEBTm between baseline and 24 h sleep deprivation. RESULTS: Sample entropy decreased after 18 h of sleep deprivation (p = 0.032) and 24 h of sleep deprivation (p = 0.001). Despite the significant main effect for the area (p = 0.012) and speed (p = 0.007) of the center of pressure, no pairwise differences were identified in the post hoc analysis. The non-dominant lower limb SEBTm composite score was reduced after 24 h of sleep deprivation (p = 0.033), and no difference was observed in the dominant limb. SIGNIFICANCE: Sleep deprivation reduced the adaptability in static postural control and dynamic stability of the non-dominant lower limb of healthy young male adults. Sample entropy seemed more sensitive to capture the effects of sleep deprivation than the classical postural control variables.

Muscle actions on crossed and non-crossed joints during upright standing and gait: A comprehensive description based on induced acceleration analysis.

The multibody nature of the musculoskeletal system makes each applied force potentially accelerate all body segments. Hence, muscles' actions on the kinematics of crossed and non-crossed joints should be estimated based on multibody dynamics. The objective of this study was to systematically investigate the actions of main lower limb muscles on the sagittal-plane angular kinematics of the hip, knee, and ankle joints, during upright standing and gait. Subject-specific simulations were performed to compute the muscle-tendon forces based on three-dimensional kinematic data collected from 10 able-bodied subjects during walking at preferred speed and during relaxed standing posture. A subject-scaled model consisting of the lower limb segments, 19 degrees of freedom and 92 Hill-type muscle-tendon units was used. Muscle-induced joint angular accelerations were estimated by Induced Acceleration Analysis in OpenSim. A comprehensive description of the estimated joint accelerations induced by lower limb muscles was presented, for upright standing and for the whole gait cycle. The observed muscle actions on crossed and non-crossed joints were phase- and task-specific. The main flexors and extensors for each joint were reported. Particular biarticular muscles presented actions opposite to their anatomical classification for specific joints. Antagonist muscle actions were revealed, such as the hitherto unknown opposite actions of the soleus and gastrocnemius at the ankle, and of the iliopsoas and soleus at the knee and ankle, during upright standing. Agonist actions among remote muscles were also identified. The presented muscle actions and their roles in joint kinematics of bipedal standing and walking contribute to understanding task-specific coordination.

Reliability of a Low-Cost Assessment of Tibial Torsion and Transverse-Plane Posture of the Lower Limb and Pelvis Using a Smartphone Compass.

OBJECTIVES: The purpose of this study was to investigate intra- and interrater reliability and minimal detectable change (MDC) of clinical measures proposed to assess tibial torsion and the posture of the lower limbs and pelvis in the transverse plane. METHODS: Twenty-five able-bodied and asymptomatic participants (mean age 27 ± 4.03, 12 women) were assessed during relaxed standing with a compass application on a smartphone coupled to a caliper. Two trained examiners measured tibial torsion and angular postures of the pelvis, hip, femur, and tibia. Intraclass correlation coefficients (ICC) were used to investigate reliabilities, and MDCs were calculated. RESULTS: The results showed predominantly good-to-excellent reliability for the measures of the femur, hip, and tibia postures and tibial torsion (0.77 < ICC < 0.94), including some moderate-to-good reliability (0.65 < ICC < 0.75). The pelvic posture measure was predominantly moderate to good (0.55 < ICC < 0.86). MDCs have been reported (2.14°-7.86°) to assist clinicians in identifying postural changes that are within or outside the random measure variation. CONCLUSION: The use of a smartphone digital compass coupled to a caliper showed to be a reliable method to assess tibial torsion and transverse-plane postures of the lower limb and pelvis.