Field-based sports require athletes to run submaximally over significant distances, often while contending with dynamic perturbations to preferred coordination patterns. The ability to adapt movement such that performance is maintained under such perturbations appears to be trainable. This may be achieved through exposure to task variability, provided there is concomitant exploration of alternate functional states through movement variability. Wearable resistance is a novel training device, which may be well suited to inducing movement variability during running given the changes to limb inertial properties. To investigate this, 14 participants performed 10 submaximal speed shuttle runs with either no weight, 1%, 3%, or 5% of body weight attached to the lower limbs. Sagittal plane lower limb joint kinematics from one complete stride cycle in each run were assessed using functional data analysis techniques. At the group-level, decreases in ankle plantarflexion following toe-off were evident in the 3% and 5% conditions, while increased knee flexion occurred during weight acceptance in the 5% condition. Individual-level between-run joint angle profiles varied, with several participants exhibiting increased joint angle variability in one or more loading conditions compared with unloaded running. Practically, 5% loading appears to constrain the movement system among certain individuals in accordance with the need to manage increased system load or the novelty of the task. For individuals in which between-run joint angle variability increased under loading, wearable resistance seemingly promoted exploration of different coordinative modes, though the magnitude of loading that elicited this response varied. Practitioners should prescribe wearable resistance individually to ensure that movement variability is encouraged without substantial alteration to or constraint of athletes’ coordinative structures.

Data collection apparatus

A 10-camera VICON motion analysis system (T-40 series, Vicon Nexus v2, Oxford, UK) sampling at 250 Hz was used for collection of kinematic data. A total of thirty-six reflective markers with 14mm diameter were attached to lower body landmarks on the pelvis, thighs, shanks, and feet according to the Plug-In-Gait model (Plug-In-Gait Marker Set, Vicon Peak, Oxford, UK).

Wearable resistance

Throughout testing, participants wore Lila^TM Exogen^TM (Sportboleh Sdh Bhd, Kuala Lumpur, Malaysia) compression shorts and calf sleeves. During WR exposure trials, a combination of 50, 100, and 200g loads totalling the required proportion of participants’ body weights were attached to the compression garments. Loads were distributed in a 2:1 thigh:shank ratio, with even distribution on anterior and posterior surfaces.

Experimental setup

Testing was undertaken on a 20 m section of the Biomechanics Laboratory at Victoria University. Motion analysis cameras were arranged around the 10 m mark of the 20 m section and the approximate capture volume was 6.0 m long, 2.5 m high, and 3.0 m, wide.

Data collection

Following application of compression garments and attachment of reflective markers, participants undertook an initial warm-up in which they ran back and forth along the 20 m section in a “shuttle” fashion for 2 min. Running speed was dictated through the use of an audible metronome, which counted each second from 1-9, before repeating for every subsequent shuttle. Participants underwent a 2 min rest period following the first warm-up run before performing a second warm-up run for 1 min at an increased speed defined by 6 s shuttle efforts. Owing to the requirement of 180^o changes of direction after each shuttle, running speeds achieved through the capture area were greater than the theoretical straight-line speed of 3.3 m.s^-1. Analysis of pilot data showed mean ± SD speeds of 4.16 ±  0.36 m.s^-1 through the capture area. Such speeds are commonly described as “striding” or “running” in field based sports, but fall below the “high-intensity” classification, often defined as >5.4 m.s^-1.

The first trial was performed with body weight only (BW), and participants completed 2 min worth of 20 m shuttles with the 6 s pacing speed per shuttle. Captures were taken each time participants passed through the 10 m mark capture area during runs from the start point to the 20 m mark only. Captures were not performed on the return shuttles. This process yielded capture of 10 complete strides across the 2 min trial.

Participants performed three subsequent 2 min running trials in which they were allocated WR loading of 1%, 3%, and 5% of body weight in a randomised order. Each trial was interspersed with a 3 min rest period. The result of this protocol was 10 complete overground running strides per condition, per participant, for analysis.

Data processing

Visual 3D software (C-motion, Rockville, MD, USA) was used to construct a seven segment model (pelvis, thighs, shanks, and feet) for each participant. Files in which several marker trajectories were lost and accurate model construction could not be performed were excluded from analysis. Out of a possible 560 files per-joint, 510 were successfully reconstructed for the hip, 530 for the knee, and 521 for the ankle. For a record of excluded files and the participants and runs to which these pertained, see S1 Table. For successfully reconstructed files, marker trajectories were smoothed via a fourth order low-pass Butterworth filter with 10 Hz cut-off frequency, based on mean residual amplitudes. Each file was trimmed to one complete stride cycle, which was defined as the period between two consecutive toe-off events on the same limb. Toe-off events were identified from the position profile of the toe marker in the z-axis. Time-continuous sagittal plane joint angles for the hip, knee, and ankle (^o) were normalised to 100% of the stride cycle for further analysis. Positive and negative joint angles were defined relative to the positions of joints in upright standing. Positive joint angles indicate positions of hip flexion, knee flexion, and ankle dorsiflexion relative to standing, while negative joint angles indicate positions of hip extension, knee extension, and ankle plantarflexion relative to standing.

Missing data values are denoted by NA values.