Older adults employ alternative strategies to operate within their maximum capabilities when ascending stairs.

Older people may operate much closer to their maximum capabilities than young adults when ascending stairs due to their lower maximum musculoskeletal capabilities. The purpose of this study was to establish the joint moment and range of motion demands of stair ascent relative to maximum capabilities in elderly and young adults. Fifteen elderly (mean age 75 years) and 17 young adult (mean age 25 years) participants ascended a purpose-built 4-step staircase with force platforms embedded into the steps and kinematic data was acquired using motion capture. Maximum musculoskeletal capabilities were assessed using a dynamometer. This study showed for the first time that stair ascent approaches the joint moment limits at the ankle in both young and older participants ( approximately 90%). One of the most important and novel findings of this study was that elderly people were only capable of meeting the high demands by adopting a number of alternative strategies not observed in young adults: (i) applying the joint moments differently than young adults across the knee and ankle, (ii) translocating energy from the knee to the ankle, thereby enhancing the ankle joint moment upon maximum demand and (iii) by enabling the plantarflexors to act over a more favourable portion of the moment-angle relation upon maximum ankle joint moment demand. The elderly displayed a more cautious strategy to optimize positional stability during stair ascent, by maintaining a smaller separation between the centre of mass and centre of pressure in the frontal plane. It seems that elderly people may meet the demands of unaided stair ascent by adopting a number of alternative strategies to compensate for their reduced musculoskeletal capabilities.

Influence of gait velocity on gastrocnemius muscle fascicle behaviour during stair negotiation.

The gastrocnemius medialis (GM) muscle plays an important role in stair negotiation. The aim of the study was to investigate the influence of cadence on GM muscle fascicle behaviour during stair ascent and descent. Ten male subjects (young adults) walked up and down a four-step staircase (with forceplates embedded in the steps) at three velocities (63, 88 and 116 steps/min). GM muscle fascicle length was measured using ultrasonography. In addition, kinematic and kinetic data of the lower legs, and GM electromyography (EMG) were measured. For both ascent and descent, the amount of fascicular shortening, shortening velocity, knee moment, ground reaction force and EMG activity increased monotonically with gait velocity. The ankle moment increased up to 88 steps/min where it reached a plateau. The lack of increase in ankle moment coinciding with further shortening of the fascicles can be explained by an increased shortening of the GM musculotendon complex (MTC), as calculated from the knee and ankle angle changes, between 88 and 116 steps/min only. For descent, the relative instant of maximum shortening, which occurred during touch down, was delayed at higher gait velocities, even to the extent that this event shifted from the double support to the single support phase.

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

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.

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.

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.

The demands of stair descent relative to maximum capacities in elderly and young adults.

In this study, we aimed to establish the joint moment and joint range of motion requirements of stair descent and the demands relative to maximal capacities in elderly and young adults. Participants descended a custom-built standard dimension four-step staircase, at their self-selected speed in a step-over manner. Kinetic data were acquired from force platforms embedded into each of the steps and into the floor at the base of the stairs. A motion analysis system was used to acquire kinematic data and joint moments were calculated using the kinematic and kinetic data. Maximum capacities (joint moment and joint range of motion) were assessed using a dynamometer. During stair descent the elderly generated lower absolute ankle joint moments than the young, which enabled them to operate at a similar relative proportion of their maximal capacity compared to young adults (75%). The knee joint moments during stair descent were similar between groups, but the elderly operated at a higher proportion of their maximal capacity (elderly: 42%; young: 30%). Ankle plantarflexion-dorsiflexion angle changes were similar between groups, which meant that the elderly operated at a higher proportion of their maximal assisted dorsiflexion angle. These results indicate that the elderly redistribute the joint moments in order to maintain the task demands within 'safe' limits.

Gastrocnemius muscle fascicle behavior during stair negotiation in humans.

The aim of the present study was to establish the behavior of human medial gastrocnemius (GM) muscle fascicles during stair negotiation. Ten healthy male subjects performed normal stair ascent and descent at their own comfortable speed on a standard-dimension four-step staircase with embedded force platforms in each step. Kinematic, kinetic, and electromyographic data of the lower limbs were collected. Real-time ultrasound scanning was used to determine GM muscle fascicle length changes. Musculotendon complex (MTC) length changes were estimated from ankle and knee joint kinematics. The GM muscle was mainly active during the push-off phase in stair ascent, and the muscle fascicles contracted nearly isometrically. The GM muscle was mainly active during the touch-down phase of stair descent where the MTC was lengthened; however, the GM muscle fascicles shortened by approximately 7 mm. These findings show that the behavior and function of GM muscle fascicles in stair negotiation is different from that expected on the basis of length changes of the MTC as derived from joint kinematics.

Knee angle-dependent oxygen consumption during isometric contractions of the knee extensors determined with near-infrared spectroscopy.

Fatigue resistance of knee extensor muscles is higher during voluntary isometric contractions at short compared with longer muscle lengths. In the present study we hypothesized that this would be due to lower energy consumption at short muscle lengths. Ten healthy male subjects performed isometric contractions with the knee extensor muscles at a 30, 60, and 90 degrees knee angle (full extension = 0 degrees ). At each angle, muscle oxygen consumption (m.VO2) of the rectus femoris, vastus lateralis, and vastus medialis muscle was obtained with near-infrared spectroscopy. m.VO2 was measured during maximal isometric contractions and during contractions at 10, 30, and 50% of maximal torque capacity. During all contractions, blood flow to the muscle was occluded with a pressure cuff (450 mmHg). m.VO2 significantly (P < 0.05) increased with torque and at all torque levels, and for each of the three muscles. m.VO2 was significantly lower at 30 degrees compared with 60 degrees and 90 degrees and m.VO2 was similar (P > 0.05) at 60 degrees and 90 degrees . Across all torque levels, average (+/- SD) m.VO2 at the 30 degrees angle for vastus medialis, rectus femoris, and vastus lateralis, respectively, was 70.0 +/- 10.4, 72.2 +/- 12.7, and 75.9 +/- 8.0% of the average m.VO2 obtained for each torque at 60 and 90 degrees . In conclusion, oxygen consumption of the knee extensors was significantly lower during isometric contractions at the 30 degrees than at the 60 degrees and 90 degrees knee angle, which probably contributes to the previously reported longer duration of sustained isometric contractions at relatively short muscle lengths.