The independent effect of added mass on the stability of the sagittal plane leg kinematics during steady-state human walking

Abstract

SUMMARYThis study investigated the independent effect of added mass on the stability of the leg kinematics during human walking. We reasoned that adding mass would influence the body's inertial state and thus challenge the ability of the leg to redirect and accelerate the total mass of the body while walking. We hypothesized that walking with added mass would reduce the stability of the leg kinematics. Lower extremity sagittal plane joint kinematics were recorded for 23 subjects as they walked on a treadmill at their preferred speed with and without added mass. The total mass of each subject was manipulated with combinations of simulated reduced gravity and added load. The stability of the leg kinematics was evaluated by computing the eigenvalues of the Poincaré map (i.e. Floquet analysis) that defined the position and velocity of the right hip, knee and ankle at heel-contact and midswing. Significant differences in stability were found between the various added mass conditions (P=0.040) and instant in the gait cycle (P=0.001). Post-hoc analysis revealed that walking with 30% added mass compromised the stability of the leg kinematics compared with walking without additional mass (P=0.031). In addition, greater instability was detected at the instance of heelcontact compared with mid-swing (P=0.001). Our results reveal that walking with added mass gives rise to greater disturbances in the leg kinematics, and may be related to the redirection and acceleration of the body throughout the gait cycle. Walking with added mass reduces the stability of the leg kinematics and possibly the overall balance of the walking pattern.

Assessing the stability of human locomotion: a review of current measures

“…However, it has never been studied whether joint angles would be even better input variables than trunk kinematics. Indeed, some studies investigating stability in patients with knee osteoarthritis and anterior cruciate ligament ruptures have used knee angle time series [37,40,42,49,50,59,72,[86][87][88][89]. The idea behind the studies in these patients was either that the main mode of instability arises from buckling or giving way of the knee joint [87] or that joint movements reflect coordination of the segments between which the joint is situated [37,40,42,49,50,59,72,86,88,89].…”

“…Another problem is how to perturb the state variables piece by piece. The first problem is usually solved by taking the mean of the trajectory crossings at a Poincaré section of a steady-state walking trial as an approximation of the fixed point [27,30,34,42,43,56,62,68,69,72,74,75,83,92,99,100], which is a reasonable assumption given that steady-state human walking has some degree of stability (i.e. humans can walk without falling every other step).…”

“…In some studies, Poincaré sections are sampled at heelstrike, or some other distinctive point in the gait cycle [27,30,72,101], based on the untested assumption that such points (e.g. heelstrike) represent biologically meaningful events within the gait cycle.…”

The metabolic cost of human running: is swinging the arms worth it?

“…The standing calibration was collected to 'zero' the anatomical reference system for each segment. The location of the markers during the standing calibration trial was used to correct for any misalignment of the local reference vectors that defined the shoulder and pelvis segment (Arellano et al, 2009). By determining the instants of initial contact using vertical ground reaction force data (Arellano and Kram, 2011), we computed the peak-to-peak amplitude of shoulder and pelvis rotation from step to step during the last 401 consecutive steps for each trial.…”

Locomotor Adaptation to an Asymmetric Force on the Human Pelvis Directed Along the Right Leg

“…Being a cable-driven system, the A-TPAD does not add undesirable mass/inertia on the user and does not undesirably constrain the human mobility. In contrast, robotic exoskeletons using rigid link members for actuation can affect human walking dynamics, as they don't actuate all the lower limb degrees-of-freedom (DOFs) and also add external mass/inertia on the human [37]- [40]. In addition, the A-TPAD can be used to perform interventions both during the swing phase and stance phase of the gait cycle as opposed to robotic exoskeletons, which typically apply external forces on the legs only during the swing phase.…”