Joint power and kinematics coordination in load carriage running: Implications for performance and injury

Highlights

• Load carriage altered inter-joint power coordination during running.

• Load carriage altered three-dimensional kinematics in running.

• The effect of load magnitude on running mechanics depended on velocity.

• Mechanical responses to load carriage may be used to guide future interventions.

Abstract

Investigating the impact of incremental load magnitude on running joint power and kinematics is important for understanding the energy cost burden and potential injury-causative mechanisms associated with load carriage. It was hypothesized that incremental load magnitude would result in phase-specific, joint power and kinematic changes within the stance phase of running, and that these relationships would vary at different running velocities. Thirty-one participants performed running while carrying three load magnitudes (0%, 10%, 20% body weight), at three velocities (3, 4, 5 m/s). Lower limb trajectories and ground reaction forces were captured, and global optimization was used to derive the variables. The relationships between load magnitude and joint power and angle vectors, at each running velocity, were analyzed using Statistical Parametric Mapping Canonical Correlation Analysis. Incremental load magnitude was positively correlated to joint power in the second half of stance. Increasing load magnitude was also positively correlated with alterations in three dimensional ankle angles during mid-stance (4.0 and 5.0 m/s), knee angles at mid-stance (at 5.0 m/s), and hip angles during toe-off (at all velocities). Post hoc analyses indicated that at faster running velocities (4.0 and 5.0 m/s), increasing load magnitude appeared to alter power contribution in a distal-to-proximal (ankle → hip) joint sequence from mid-stance to toe-off. In addition, kinematic changes due to increasing load influenced both sagittal and non-sagittal plane lower limb joint angles. This study provides a list of plausible factors that may influence running energy cost and injury risk during load carriage running.

Introduction

Running related sports which require load carriage (e.g. ultra-marathon) have become increasingly popular over the past two decades [1], [2]. However, compared with walking research into load carriage [3] running mechanics has received little attention [4], [5], with prior investigations focusing mainly on military applications [5], [6]. Within the military setting, overuse lower limb injuries are commonly associated with heavy load carriage which may involve both walking and running [7]. However, epidemiological evidence of a detrimental effect of load on non-military athletes is lacking. Research into loaded running in civilians is required to increase our understanding of the impact of load carriage on running energy cost [8] and injury risks [9].

The mechanics of running without external load (termed unloaded running) are well understood. Prior to mid-stance, the knee and ankle extensors absorb power to decelerate the body segments and support body weight (BW) [10], [11]. During push-off, power to accelerate the body into flight is largely driven by the ankle extensors [10], [11]. This temporal coordination in power flow likely reflects muscle coordination patterns which provide the required energy in running while minimizing metabolic cost [10], [12]. Interestingly, it has been reported that increasing load magnitude in running does not alter the proportional contribution of hip, knee and ankle when considering average positive power [5]. However, when considering phase-specific gait effects, a previous study in walking reported that load carriage did influence joint power [3]. In running, it is yet unknown how each joint contributes to the total power across the stance phase, when load is carried. In addition, since previous studies have found different joint power contributions at different velocities [13], the effect of load on running joint power control may vary at different velocities.

An in-depth analysis of three dimensional (3D) joint angles is needed in this area, as changes to joint kinematics alter joint power contributions [14] and soft-tissue strain patterns [15], [16]. For example, small alterations in knee flexion angle (e.g. 4°) has been shown to increase knee joint positive work by 2.5 J/kg [14] and increase the magnitude of knee joint load [17]. Current studies have only investigated the effects of load on sagittal plane kinematics in running at relatively slow velocities [4], [5]. However, load carriage exerts significant non-sagittal plane torque on the body [18], which when coupled with insufficient muscle capacity, may result in deviations of non-sagittal plane kinematics and create asymmetrical soft-tissue stresses [15]. Since loaded running occurs across a range of velocities and joint internal loads increase at faster running velocities [19], investigating the effect of load in 3D whilst running at a range of velocities is needed.

With an increasing involvement of people in running sports requiring load carriage, detailed research into the effect load carriage has on running mechanics is warranted to facilitate the management of these athletes. Statistical Parametric Mapping (SPM) has been used to perform hypothesis testing on biomechanical time-series data [20], which provides a more robust statistical method for understanding the phase-specific effects of load on running mechanics. Thus, the aim of this study is to determine the phase-specific effect of running with three different loads across three different velocities on joint power and 3D kinematics over the stance phase.