The purpose was to compare step-by-step kinematics measured using force plates (criterion), an IMU only and a combined laser IMU system in well-trained sprinters. Fourteen male experienced sprinters performed a 50-m sprint. Step-by-step kinematics were measured by 50 force plates and compared with an IMU-3D motion capture system and a combined laser+IMU system attached to each foot. Results showed that step kinematics (step velocity, length, contact and flight times) were different when measured with the IMU-3D system, compared with force plates, while the laser+IMU system, showed in general the same kinematics as measured with force plates without a systematic bias. Based upon the findings it can be concluded that the laser+IMU system is as accurate in measuring step-by-step kinematics as the force plate system. At the moment, the IMU-3D system is only accurate in measuring stride patterns (temporal parameters); it is not accurate enough to measure step lengths (spatial) and velocities due to the inaccuracies in step length, especially at high velocities. It is suggested that this laser+IMU system is valid and accurate, which can be used easily in training and competition to obtain step-by step kinematics and give direct feedback of this information during training and competition.

Background: Static stretching (SS) is routinely used in sports and clinical settings to increase joint range of motion (ROM). However, the mechanisms underlying improvements in ROM remain unclear. Objective: We aimed to determine the effects of a single session (acute) and multiple sessions (chronic) of SS on stretch tolerance, passive stiffness and fascicle length, and whether such effects are moderated by specific training parameters and participant characteristics. A secondary aim was to explore the mechanisms associated with improved ROM. Methods: Seven databases (CINAHL Complete, Cochrane CENTRAL, Embase, Emcare, MEDLINE, Scopus and SPORTDiscus) were systematically searched up to 6 June, 2024. Randomised and non-randomised controlled trials investigating the effects of acute (single session) or chronic (two or more sessions) SS on muscle–tendon unit structure (fascicle length), mechanical properties (stiffness) or stretch tolerance (maximum tolerable passive resistive torque) compared to non-stretching passive controls (adults aged ≥ 18 years) were included. The effects of SS were examined using a multi-level meta-analysis, with associations between changes in maximum tolerable passive resistive torque, stiffness and fascicle length with improvements in ROM examined using multivariate meta-regression. Results: Data from 65 studies representing 1542 adults (71% male; mean ± standard deviation age = 26.1 ± 11 years) were included. We found a small decrease in overall stiffness following both acute (Hedges’ g = 0.42, 95% confidence interval [CI] 0.21, 0.63, p < 0.001) and chronic SS (Hedges’ g = 0.37, 95% confidence interval 0.18, 0.56, p < 0.001), and a moderate increase in maximum tolerable passive resistive torque following chronic SS (Hedges’ g = 0.74, 95% CI 0.38, 1.10, p < 0.001). Neither acute nor chronic SS had a significant effect on fascicle length. For acute SS, greater reductions in overall stiffness were found with moderate (p < 0.002) and high SS intensities (p = 0.02) compared with low-intensity SS, and in individuals with normal flexibility compared with those with poor flexibility at baseline (p < 0.001). Conversely, the effects of chronic SS on overall stiffness and maximum tolerable passive resistive torque were not moderated by stretching intensity, intervention length, baseline flexibility or sex (p > 0.05). Last, improved ROM following chronic SS was significantly associated with both decreased overall stiffness (g = 0.59, 95% CI 0.08, 1.10, p = 0.03) and increased maximum tolerable passive resistive torque (g = 0.74, 95% CI 0.41, 1.09, p < 0.001). Conclusions: While both acute and chronic SS reduced overall stiffness, stretch tolerance only increased following chronic SS. Neither acute nor chronic SS altered fascicle length. The effect of acute SS on reduced overall stiffness was greater when stretching at a moderate or higher intensity and in those with normal flexibility. Increased ROM was significantly associated with decreased overall stiffness and increased stretch tolerance following chronic SS. Understanding the mechanisms underlying SS will assist coaches and clinicians in deciding whether and when to prescribe SS to their athletes and patients. Clinical Trial Registration: PROSPERO CRD42023420168.

The purpose of this study was to elucidate pelvic orientation angles using a single lower back-mounted inertial sensor during sprinting. A single inertial sensor was attached to each sprinter’s lower back, used to measure continuous pelvic movements including pelvic obliquity (roll), anterior-posterior tilt (pitch) and rotation (yaw) during sprinting from a straight to bend section. The pelvic orientation angles were estimated with the three-dimensional sensor orientation using a sensor fusion algorithm. Absolute angles derived from the sensor were compared with angles obtained from an optical motion capture system over a 15 m length. The root mean squared error between the sensor and motion capture data were 4.1° for roll, 2.8° for pitch and 3.6° for yaw. Therefore, the sensor was comparable to the motion capture system for tracking pelvic angle changes. The inertial sensor is now supported as a valid tool to measure movements of the pelvis during sprinting.

This study elucidated kinetic and kinematic changes between control and weighted vest sprinting with a load of 7% body mass. Fourteen male sprinters completed 60 m control and vest sprints over a long force platform system. Step-to-step ground reaction force and spatiotemporal variables were grouped, representing the initial acceleration (1st-4th steps), middle acceleration (5th-14th steps), later acceleration (15th step-step before maximum velocity reached) and maximum velocity (stride where maximum velocity reached) phase during each trial. Two-way ANOVA with post hoc Tukey HSD and a Cohen's d effect size with 95% confidence intervals elucidated the difference between trials and phases. Between control and vest trials the velocity decreased (3.41-3.78%) through trivial-small step length (1.95-2.72%) and frequency (0.87-1.54%) decreases. Vertical impulse increased (6.46-6.78%) through moderate support time increases (4.84-6.00%), coupled with no effective vertical mean force differences during the vest trial, compared to the control. There was no significant interaction between trials and phases. Therefore, although weighted vest trials did not increase vertical mean force production, vests did induce an increased vertical force application duration during the support phase step-to-step while supporting a larger total load (body mass plus vest mass).