M. Spanjaard

Influence of light handrail use on the biomechanics of stair negotiation in old age

The high incidence of falls in older adults during stair negotiation suggests that this task is physically challenging and potentially dangerous. The present study aimed to examine the influence of light handrail use on the biomechanics of stair negotiation in old age. Thirteen older adults ascended and descended a purpose-built staircase at their self-selected speed: (i) unaided and (ii) with light use of the handrails. Ground reaction forces (GRFs) were measured from force platforms mounted into each step and motion capture was used to collect kinematic data. Knee and ankle joint moments were calculated using the kinetic and kinematic data. The horizontal separation between the centre of mass (COM) and the centre of pressure (COP) was assessed in the sagittal and frontal planes. During stair ascent, handrail use caused a different strategy to be employed compared to unaided ascent with a redistribution of joint moments. Specifically, the ankle joint moment (of the trailing leg) was reduced with handrail use, which has previously been shown to approach its limits during unaided stair ascent, but the knee joint moment (of the leading leg) increased. Previous research has shown that a larger joint moment reserve is available at the knee during unaided stair ascent. During stair descent, the ankle joint moment increased with handrail use, this was associated, however, with a more effective control of balance as shown by a reduced COM-COP separation in the direction of progression compared to unaided descent. These results indicate that although the biomechanical mechanisms are different for stair ascent and descent, the safety of stair negotiation is improved for older adults with light use of the handrails.

Lower-limb biomechanics during stair descent: influence of step-height and body mass

SUMMARY The aim of the present study was to examine the biomechanics of the lower limb during stair descent and the effects of increasing demand in two ways: by increasing step-height and by increasing body mass. Ten male subjects walked down a four-step staircase, the height of which could be altered. The step-heights were: standard (17 cm), 50% decreased, 50% increased and 75% increased. At the standard height, subjects also walked down wearing a weighted jacket carrying 20% extra body mass. Lower limb kinematics and kinetics were determined using motion capture and ground reaction forces. Also measured were gastrocnemius medialis (GM) muscle electromyography and GM muscle fascicle length using ultrasonography. GM muscle fascicles actively shortened during the touch-down phase of stair descent in all conditions, while the muscle–tendon complex (MTC), as calculated from the knee and ankle joint kinematics, lengthened. The GM muscle fascicles shortened more when step-height was increased, which corresponded to the increase in ankle joint moment. Increased body mass did not alter the ankle or knee joint moment in the first contact phase of a step down; due to a change in strategy, the trailing leg, instead of the leading leg, supported the extra mass. Hence, the amount of GM muscle fascicle shortening, during the touch-down phase, also did not change with added body mass. Our results suggest that the increase in joint moments is related to the amount of fascicle shortening, which occurs whilst the MTC is lengthening, thereby stretching the elastic tendinous tissues.

Mechanics of toe and heel landing in stepping down in ongoing gait

When stepping down from a height difference in ongoing gait, subjects are known to use a heel landing at small height differences and switch to toe landing for larger height differences. We hypothesized that in toe landing, the leading leg can perform more negative work, to control the momentum gained during the descent, than in heel landing. Ten young male participants walked over a 10-m walkway at 5km/h to step down a height difference of 10cm halfway, using a heel or toe landing in five trials each. Kinematic data and ground reaction forces under the leading and trailing legs were recorded. Inverse dynamical analysis of both strategies showed that the leading leg performed more negative work in toe landing, while the vertical velocity at ground contact was lower. In addition, the impact forces were lower in toe landing than in heel landing. Toe landing was found to reduce gait velocity in the first step on the lower level and required higher moments and negative power around the ankle joint than heel landing. Our results indicate that heel landing may be preferred when stepping down small height differences, because it is less demanding especially for the plantar flexor muscles, while toe landing may be preferred for stepping down larger height differences, because it improves control over the momentum gained during the descent.

Influence of step-height and body mass on gastrocnemius muscle fascicle behavior during stair ascent

To better understand the role of the ankle plantar flexor muscles in stair negotiation, we examined the effects of manipulation of kinematic and kinetic constraints on the behavior of the gastrocnemius medialis (GM) muscle during stair ascent. Ten subjects ascended a four-step staircase at four different step-heights (changing the kinematic constraints): standard (17 cm), 50% decreased, 50% increased and 75% increased. At the standard height, subjects also ascended the stairs wearing a weighted jacket, adding 20% of their body mass (changing the kinetic constraints). During stair ascent, kinematics and kinetics of the lower legs were determined using motion capture and ground reaction force measurements. The GM muscle fascicle length was measured during the task with ultrasonography. The amount of GM muscle fascicle shortening increased with step-height, coinciding with an increase in ankle joint moment. The increase in body mass resulted in an increased ankle joint moment, but the amount of GM muscle fascicle shortening during the lift-off phase did not increase, instead, the fascicles were shorter over the whole stride cycle. Increasing demands of stair ascent, by increasing step-height or body mass, requires higher joint moments. The increased ankle joint moment with increasing demands is, at least in part, produced by the increase in GM muscle fascicle shortening.

EFFECT OF GAIT VELOCITY ON HUMAN GASTROCNEMIUS FASCICLE BEHAVIOR DURING STAIR DESCENT

present study, fascicular shortening of the GM muscle is investigated at different gait velocities. Ankle joint moment would be expected to increase with increasing gait velocity, hence it is hypothesized that GM muscle fascicles will shorten more at a higher gait velocity. METHODS Ten young adult male subjects performed stair ascent at 3 different velocities (63, 88 and 116 step/min, controlled using a metronome). Kinematics and kinetics of the lower legs were measured using a 9-camera VICON system and a 4-step staircase with embedded forceplates. Ultrasound was used to determine muscle fascicle behavior; a lineararray probe (60mm probe width) was placed at the midsagittal plane of the left GM muscle, and tightly secured with a custom build fixation device. GM muscle fascicle length and pennation angle were measured for every frame in the stride from the first to the third step. To account for inter-individual fascicle length differences, values were calculated relative to a reference length, which was measured when standing upright. Influence of velocity was investigated for the stride period in which the muscle was active (assessed from Electrical activity (EMG) measurements): during the push-off phase, from peak EMG until lift-off. General Estimated Equations (GEE) were used for statistical analysis. RESULTS AND DISCUSSION During push-off, the ankle plantar-flexed caused by GM muscle fascicle shortening. At higher velocities, GM EMG was higher and peaked relatively earlier, while lift-off was also relatively early at higher velocities. Fascicle shortening increased in magnitude (1.3, 2.3 and 4.2 cm [mean] for resp. 63, 88 and 116 st/min, p<0.05) and shortening velocity (p<0.05) with increasing gait velocity. The increased shortening at higher velocities caused a higher ankle moment (p<0.05), however, the ankle moment did not increase any further beyond 88 st/min (p=0.628). Therefore, the increase in GM muscle fascicle shortening beyond 88 st/min can be explained by the shorter MTC length at 116 compared to that at 88 st/min (p<0.05), there was no difference in MTC length between 63 and 88 st/min (p=0.241). The results of the present study indicate that increases in fasci