The effect of increasing inertia upon vertical ground reaction forces and temporal kinematics during locomotion

Abstract

SUMMARYThe addition of inertia to exercising astronauts could increase ground reaction forces and potentially provide a greater health benefit. However, conflicting results have been reported regarding the adaptations to additional mass (inertia) without additional net weight (gravitational force) during locomotion. We examined the effect of increasing inertia while maintaining net gravitational force on vertical ground reaction forces and temporal kinematics during walking and running. Vertical ground reaction force was measured for 10 healthy adults (five male/five female) during walking (1.34·m·s -1 ) and running (3.13·m·s -1 ) using a force-measuring treadmill. Subjects completed locomotion at normal weight and mass and at 10, 20, 30 and 40% of added inertial force. The added gravitational force was relieved with overhead suspension, so that the net force between the subject and treadmill at rest remained equal to 100% body weight. Ground reaction forces were affected by the added inertial force, but not to the magnitude predicted by the increase in mass, suggesting that adaptations in motion occurred. Vertical ground reaction force production and adaptations in gait temporal kinematics were different between walking and running. Peak vertical impact forces and loading rates increased with increased inertia during walking, and decreased during running. As inertia increased, peak vertical propulsive forces decreased during walking and did not change during running. Stride time increased during walking and running, and contact time increased during running. The increased inertial forces were utilized independently from gravitational forces by the motor control system when determining coordination strategies.

Biomechanical Analysis Comparing Titanium Elastic Nails With Locked Plating in Two Simulated Pediatric Femur Fracture Models

“…This load exceeded considerably the compressive loads seen by the femur under physiological conditions of running. 17 The constructs were then compared with one another with respect to each of the fracture patterns using SPSS statistical software (SPSS Inc., Chicago, IL). Descriptive statistics are reported and groups were compared using Student t test.…”

Effect of added inertia on the pelvis on gait

“…Results are an increase of energetics [6] and muscle activity [7]. Gait parameters remained unchanged [8] or change hardly (<3% [7]). The effect of pure inertia on gait kinematics has not been assessed, however the effect of added weight has.…”

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

“…Based on our experimental design, we infer that the leg kinematics were less stable because the added mass influenced the inertial state of the body throughout the walking gait cycle (De Witt et al, 2008). Changes in the body's inertial state appear to create small disturbances in the leg kinematics while walking.…”

“…The influence of mass alone on the biomechanics of walking has been experimentally explored by first adding weight to the subject and then counteracting the forces due to gravity with a body weight suspension system (De Witt et al, 2008;Grabowski et al, 2005). The upward lifting force provided by the suspension system compensates for the gravitational forces such that the subject's weight is maintained but the subject's overall mass is increased.…”

“…Thus, adding mass without adding weight increases the amount of mass that the legs must redirect and accelerate throughout the gait cycle. Using the combination of body weight support and added weight, it has been demonstrated that walking under the influence of added mass alone increases metabolic cost and affects the velocity of the center of mass (De Witt et al, 2008;Grabowski et al, 2005). These results suggest that the acceleration and redirection of the body's mass throughout the gait cycle is important for the maintenance of the steady-state walking pattern.…”