Small wireless trunk accelerometers have become a popular approach to unobtrusively quantify human locomotion and provide insights into both gait rehabilitation and sports performance. However, limited evidence exists as to which trunk accelerometry measures are suitable for the purpose of detecting movement compensations while running, and specifically in response to fatigue. The aim of this study was therefore to detect deviations in the dynamic center of mass (CoM) motion due to running-induced fatigue using tri-axial trunk accelerometry. Twenty runners aged 18–25 years completed an indoor treadmill running protocol to volitional exhaustion at speeds equivalent to their 3.2 km time trial performance. The following dependent measures were extracted from tri-axial trunk accelerations of 20 running steps before and after the treadmill fatigue protocol: the tri-axial ratio of acceleration root mean square (RMS) to the resultant vector RMS, step and stride regularity (autocorrelation procedure), and sample entropy. Running-induced fatigue increased mediolateral and anteroposterior ratios of acceleration RMS (p < .05), decreased the anteroposterior step regularity (p < .05), and increased the anteroposterior sample entropy (p < .05) of trunk accelerometry patterns. Our findings indicate that treadmill running-induced fatigue might reveal itself in a greater contribution of variability in horizontal plane trunk accelerations, with anteroposterior trunk accelerations that are less regular from step-to-step and are less predictable. It appears that trunk accelerometry parameters can be used to detect deviations in dynamic CoM motion induced by treadmill running fatigue, yet it is unknown how robust or generalizable these parameters are to outdoor running environments.

Fatigue, developed over the course of a run, may cause changes in running kinematics. Training status may influence the effect of fatigue on running kinematics, since well trained, competitive runners are used to running until exhaustion, whereas novice runners are not. This study aimed to determine changes in running kinematics during an exhaustive run in both novice (NOVICE) and competitive (COMP) long-distance runners. About 15 NOVICE and 15 COMP runners performed a treadmill run, until voluntary exhaustion at 3,200 m time trial pace. Joint angles and global trunk and pelvis angles were recorded at the beginning and at the end of the run. In both groups, peak pelvic anterior tilt, pelvic rotation range of motion (both during stance phase) and ankle plantar flexion during swing phase increased after the exhaustive run. There was a significant interaction effect between group and exhaustion for peak forward trunk lean, which increased only in the NOVICE group, and for hip abduction during mid-swing, which increased in NOVICE and decreased in COMP runners. In conclusion, NOVICE runners showed larger kinematic adjustments when exhausted than COMP runners. This may affect their running performance and should be taken into account when assessing a runner's injury risk.

The effect of running training on running kinematics and kinetics in novice runners has not yet been investigated. Previous studies have shown that novice runners are less economical and more prone to injury compared to well-trained runners. Since running economy (RE) and running injury risk have been associated with biomechanical variables that may be trainable, the purpose of this study was to determine the effect of a 12-week training program for beginners on running kinematics and kinetics. It was hypothesised that participants would evolve towards running kinematics and kinetics that have previously been associated with better RE and lower injury risk. 27 participants underwent a full-body, threedimensional running analysis before and after a 12-week running program. Outcome variables included peak joint angles, joint moments, and ground reaction forces (GRF) in three planes. After training, hip external rotation moment increased significantly with 0.01 Nm/kg. Peak vertical GRF decreased with 0.9 N/kg (4.05%). There were no significant changes in peak joint angles. In conclusion, results show that a 12-week running program for beginners aimed to increase running endurance does not lead to changes in running kinematics or kinetics that have previously been associated with better RE and lower injury risk.

Performing submaximal bouts of knee extensor contractions, while monitoring EMG and deoxygenation, seems a feasible manner to estimate an aerobic capacity-related exercise intensity of peripheral fatigue onset. This test may be used to evaluate changes in endurance capacity of single muscle groups, without the necessity for all-out testing, which could be problematic with frail subjects.

IntroductionAchilles tendinopathy is a common overuse injury in runners and related to maladaptation of the Achilles tendon. The aim of the present review is to provide an overview of the literature on the adaptation of the Achilles tendon to running and the maladaptation caused by overloading of the tendon that leads to Achilles tendinopathy. Discussion Cross-sectional studies reveal that runners have thicker Achilles tendons than non-runners, but no difference in its stiffness is found. Patients with Achilles tendinopathy have a larger Achilles tendon cross-sectional area, but lower stiffness than those of healthy people. Longitudinal studies on the adaptation of Achilles tendon mechanical properties are scarce and do not find a change in Achilles tendon size or stiffness. ConclusionMore longitudinal studies are necessary to find out what magnitude of strain is needed to trigger an adaptational response in tendons and to define a threshold between loading and overloading of the Achilles tendon.