Maintaining and increasing walking speed in old age is clinically important because this activity of daily living predicts functional and clinical state. We reviewed evidence for the biomechanical mechanisms of how strength and power training increase gait speed in old adults. A systematic search yielded only four studies that reported changes in selected gait biomechanical variables after an intervention. A secondary analysis of 20 studies revealed an association of r2 = 0.21 between the 22% and 12% increase, respectively, in quadriceps strength and gait velocity in 815 individuals age 72. In 6 studies, there was a correlation of r2 = 0.16 between the 19% and 9% gains in plantarflexion strength and gait speed in 240 old volunteers age 75. In 8 studies, there was zero association between the 35% and 13% gains in leg mechanical power and gait speed in 150 old adults age 73. To increase the efficacy of intervention studies designed to improve gait speed and other critical mobility functions in old adults, there is a need for a paradigm shift from conventional (clinical) outcome assessments to more sophisticated biomechanical analyses that examine joint kinematics, kinetics, energetics, muscle-tendon function, and musculoskeletal modeling before and after interventions.

The purpose of this project is to conduct a comprehensive and systematic scoping review to identify and document the breadth of literature related to physical activity-related injuries in older adults. The population of interest was adults (both males and females) over the age of 65 years, participating in exercise, leisure-time, or sport-type physical activities. The initial search yielded 16,828 articles, with 43 articles ultimately included. The final 43 articles utilized the following study designs: three experimental (two randomized control and one non-randomized control), 14 prospective studies, and 26 retrospective. The results of this scoping review would suggest that it may be premature to provide definitive incidence rates, causes, and correlates of physical activity-related injuries in older adults. However, the current literature does not suggest that older adults are at an increased risk of injury from participation in physical activities. Future research should utilize a consistent definition of 'injury' and consistent and comprehensive descriptors of injuries-including intensity level of engagement of activity and burden/severity of injury. In addition, injury rates in specific populations are needed, particularly for the oldest-old, for those in assisted-living situations, and for subgroups with clinical conditions. Finally, greater surveillance and documentation of older adult initiatives and interventions are needed in order to identify programs successful in reducing the injury rates of their target populations.

Purpose: As a highly heterogeneous group, seniors live in complex environments influenced by multiple physical and social structures that affect their safety. Until now, the major approach to falls research has been person centered. However, in industrial settings, the individuals involved in an accident are seen as the inheritors of system defects. The objective of the present study was to investigate safety deficiencies that contributed to falls in community-dwelling seniors using a systems approach. Design and Methods: The investigations were conducted using the Seniors Falls Investigation Methodology (SFIM), an adapted version of a method used to examine transportation accidents, such as airplane crashes. Fifteen seniors, who experienced a fall or near fall, participated in multiple case studies. A cross-case synthesis was used to summarize findings and identify common patterns of causes and safety deficiencies. Results: Falls and near falls are a result of latent unsafe conditions, and unsafe acts and decisions combined in a diverse set of circumstances. If not identified and removed, these unsafe conditions can cause falls for other seniors. Implications: This study provided compelling evidence that causes of falling are systemic and develop over time. It demonstrated that the systems approach is needed to expand the focus from the individual to multilayered organizational and supervisory causes. The SFIM demonstrated capability to identify causes of falls that will allow better prevention and management programs, hence advancing seniors’ safety. SFIM shows great potential for implementation in organized settings, such as hospitals and long-term care homes.

OBJECTIVE:To test the hypothesis that selected gait kinematics, particularly lateral trunk lean, observed in patients with medial compartment knee osteoarthritis explain variation in dynamic knee joint load.METHOD:In this cross-sectional observational study, 120 patients with radiographically confirmed varus gonarthrosis underwent three-dimensional gait analysis at their typical walking speed. We used sequential (hierarchical) linear regression to examine the amount of variance in dynamic knee joint load (external knee adduction moment) explained by static lower limb alignment (mechanical axis angle) and gait kinematics determined a priori based on their proposed effect on knee load (walking speed, toe-out angle, and lateral trunk lean angle).RESULTS:Approximately 50% of the variation in the first peak external knee adduction moment was explained by mechanical axis angle (25%), Western Ontario and McMaster Universities Osteoarthritis Index pain score (1%), gait speed (1%), toe-out angle (12%), and lateral trunk lean angle (13%). There was no confounding or interaction with Kellgren and Lawrence grade of severity.CONCLUSIONS:Gait kinematics, particularly lateral trunk lean, explain substantial variation in dynamic knee joint load in patients with medial compartment knee osteoarthritis. While largely ignored in previous gait studies, the effect of lateral trunk lean should be considered in future research evaluating risk factors and interventions for progression of knee osteoarthritis.

Resistance exercise may counteract the sarcopenia associated with aging. The safety considerations of such exercise have not been fully determined. Previously, we have investigated cardiovascular responses to submaximal isokinetic resistance exercise. The purpose of the current study was to compare heart rate and blood pressure responses to maximal, typical isokinetic eccentric (ECC) and concentric (CON) resistance exercise protocols in healthy active older adults. In random order, subjects (n = 20, 74 ± 7y, 10 males) performed maximal ECC and CON isokinetic knee extension exercise (90° 3×10 reps, 5s rep rest, 2 min set rest). Heart rate (HR), and systolic (SBP) and diastolic (DBP) blood pressures were measured continuously and recorded every 15 seconds (Finapres). Mean arterial blood pressure [MAP; DBP+1/3(SBP-DBP)] and rate-pressure product (RPP; HRxSBP/100) were calculated. Mean ECC exercise torque (90 Nm) was significantly (p < .001) greater than mean CON exercise torque (59 Nm). HR, MAP, and RPP increased significantly (p < .001) in each set of ECC and CON exercise. Maximal CON exercise elicited greater (p < .01) increases in MAP and RPP than maximal ECC exercise despite the fact that ECC exercise was performed at a significantly greater torque output than CON exercise. These results may have implications for isokinetic training and rehabilitation programs for older adults.

OBJECTIVE:To evaluate the effects of a functional knee brace specifically designed for patients with varus gonarthrosis on measures of proprioception and postural control.SUBJECTS:Fourteen men and six women (aged 59+/-9 yr) with measurable varus alignment and osteoarthritis of the knee medial compartment.METHODS:Proprioception was assessed in the sitting position using an isokinetic dynamometer and was quantified as the ability to replicate target knee-joint angles. Postural control was assessed with a force platform using tests of single-limb standing balance performed, while the patient was standing on a stable surface and standing on foam, and was quantified as the total length of the path of the centre of pressure. All tests were performed with and without the patient's own custom-fit valgus brace.RESULTS:Proprioception was significantly improved following application of the brace [mean difference=0.7 degrees, 95% confidence interval (CI)=0.2 to 1.1 degrees ). Postural control was not significantly affected by the use of the brace during the stable surface test (mean difference=2.6 cm, 95% CI=-4.3 to 9.5 cm) or the foam surface test (mean difference=0.9 cm, 95% CI=-7.5 to 9.4 cm).CONCLUSION:Although enhanced proprioception may be partially responsible for reported improvements with the use of a brace, the present findings call into question the functional importance of the small changes observed.

Sarcopenia associated with the normal aging process is often combined with the detrimental effects of a sedentary lifestyle in older adults, leading to a significant reduction in reserve capacity of the neuromuscular system. A clear example of the aging effect is the pattern of reduction in muscle strength after the sixth decade for both isometric and concentric contractions. However, older adults are relatively stronger for movements in which muscles lengthen, due to the inherent advantage of eccentric contractions, plus their stiffer muscle structures and prolonged myosin cross-bridge cycles. Also, the capacity for physiological adaptations in the motor pathways remains into very old age when an appropriate exercise stimulus is given, and older adults can obtain adaptations in both enhanced neural control of motor units and increased protein synthesis leading to moderate muscle hypertrophy. Since periods of sedentary lifestyle or bed rest due to illness can have severe detraining consequences on the neuromuscular function of an older person, long-term prevention strategies are advocated to avoid excessive physical impairments and activity restrictions in this age group.

This study quantifies concentric and eccentric dorsiflexor muscle torque at various movement velocities and determines the neuromuscular effects from short-term practice of repeated maximal voluntary contractions using an isokinetic resisted exercise program in older adults. Twenty-eight subjects (76.3+/-4.6 years) trained concentric and eccentric dorsiflexion 3 days per week for 2 weeks at 30 degrees, 90 degrees, and 180 degrees/s through 40 degrees of dorsiflexion range of motion. Peak torque, rate of torque development, surface electromyography, and strength curves at each velocity were compared before and after training. Increases were found for concentric (27%) and eccentric (20%) dorsiflexor peak torque and concentric rate of torque production (20%-53%) across all movement velocities (p < .01). Training also significantly increased dorsiflexor concentric (64%) and eccentric (55%) surface electromyography; taken together, this is evidence of apparent adaptation of neural factors in older adults with short-term training. These findings support that eccentric and concentric strength training enhances the control and production of ankle muscle dorsiflexor torque in older adults, with implications for improving functional mobility of the ankle joint.

The effects of aging on motoneuron firing rates and muscle contractile properties were studied in tibialis anterior muscle by comparing results from six young (20.8 +/- 0.8 yr) and six old men (82.0 +/- 1.7 yr). For each subject, data were collected from repeated tests over a 2-wk period. Contractile tests included maximal voluntary contraction (MVC) with twitch interpolation and stimulated twitch contractions. The old men had 26% lower MVC torque (P < 0.01) than did the young men, but percent activation was not different (99.1 and 99.3%, respectively). Twitch contraction durations were 23% longer (P < 0.01) in the old compared with the young men. During a series of repeated brief steady-state contractions at 10, 25, 50, 75, and 100% MVC, motor unit firing rates were recorded. Results from approximately 950 motor unit trains in each subject group indicated that at all relative torque levels mean firing rates were 30-35% lower (P < 0.01) in the old subjects. Comparisons between young and old subjects' mean firing rates at each of 10%, 50%, and MVC torques and their corresponding mean twitch contraction duration yielded a range of moderate-to-high correlations (r = -0.67 to -0.84). That lower firing rates were matched to longer twitch contraction durations in the muscle of old men, and relatively higher firing rates were matched with shorter contraction times from the young men, indirectly supports the neuromuscular age-related remodeling principle.

1989 We compared heart rate (HR), mean arterial blood pressure (MAP) and rate-pressure product (RPP) responses to submaximal isokinetic concentric (CON) and eccentric (ECC) knee extension exercise at the same absolute torque output in 20 young (M&SD=23.2&1.7yr) and 20 older (M=75.2&4.6yr)adults. After determination of peak CON and ECC torques, subjects performed separate, randomly ordered, two-minute bouts of CON and ECC exercise at 90 degrees/s (exercise intensity = 50% of CON peak torque). Peak torques were higher (p<0.001) in ECC exercise, and were also higher (p<0.001) in younger vs. older adults for both CON and ECC exercise. HR, MAP, and RPP increased (p<.001) throughout the exercise bouts for both age groups. CON exercise elicited a greater HR, MAP, and RPP response than ECC exercise (p<0.001) for both age groups. There was no difference in peak HR or RPP between young and older adults for either type of contraction, however, peak MAP was higher in the older adults. Thus, at the same absolute torque output, isokinetic CON knee extension exercise elicited a significantly greater level of cardiovascular stress than ECC exercise in both young and old adults. These results have implications for determining appropriate fitness and rehabilitation programs for older adults. Supported by the Natural Sciences and Engineering Research Council

1169 The purpose was to compare the effects of aging on the relationship between whole muscle contractile properties and motor unit (MU) firing rates in the human tibialis anterior (TA) and quadriceps muscles. Twitch properties and intramuscular EMG recordings were collected from 15 old (74-85y) and 19 young(20-31y) men. MU action potential (AP) trains were recorded using tungsten microelectrodes during repeated contractions at 10, 25, 50, 75 and 100% of maximum voluntary contraction (MVC). Using shape recognition and manual overlay of APs, individual trains were identified and firing rates were determined for >900 different MUs per muscle per age group. Compared with the young, MVC forces were 36% less (p<0.01) in TA and 48% less (p<0.01) in quadriceps. Twitch interpolation indicated that during MVCs, both young and old men were able to activate maximally each muscle (>94%). Twitch contraction properties were significantly slower in the old men compared with the young. In the TA, MU firing rates at all force levels were lower (12 - 50%, p<0.01) in old men compared with young, however, for quadriceps there were no age-related differences in firing rates. Thus, an age-related association between firing rates and contractile properties was found in the TA, but not in quadriceps. Therefore, remodelling of the aged neuromuscular system may be related to anatomic differences, and functional use of muscles during daily activity.

Fatigue and recovery from a period of intermittent isometric exercise have received little research attention in older adults. Here we report data from six old (80 ± 5 y) and four young men (27 ± 2 y) who performed a 50% of maximum voluntary contraction (MVC) quadriceps fatigue protocol as described by Bigland-Ritchie et al (JAP 61:42, 1986). MVC force, surface EMG, and electrically evoked contractile properties were recorded at the beginning and at every minute during the test. Subjects exercised until their MVC was reduced to ≈50%, or they could not continue. The same parameters were recorded post-fatigue at 1, 3, 5 and 10 minutes. In agreement with the study cited above, results from the young group showed a parallel decline in MVC and 50Hz tetanic force, whereas twitch amplitudes declined at a faster rate. In addition, by the end of the fatigue test, the integrated EMG(IEMG) of the 50% target force approached the MVC IEMG. The men in the old group showed similar responses to fatigue. During recovery, however, the MVC force of the young subjects returned to pre-fatigue levels (≥99%) by 10 min, but force was only ≈85% recovered (p≤0.05) for the old men. Similarly, peak twitch tensions tended to return to pre-fatigue values faster in the young than in the old. Target and MVC IEMGs recovered to near pre-fatigue values similarly in both groups. Results suggest that although the old men fatigue in a similar manner as the young, their force recovery is significantly reduced. Central drive, as measured by IEMG, does not seem to account for this age-related force depression during 10 minutes of recovery.

Although a number of mechanical and neuromuscular processes have been identified, the primary mechanisms underlying residual functional instability of the ankle remain unclear. Understanding such mechanisms will help physical therapists identify where to focus treatment efforts, ultimately leading to more effective rehabilitation. In the present investigation, resistive torque at maximum ankle inversion was evaluated to determine if lateral ankle structures demonstrated mechanical laxity. Thirty subjects with a history of unilateral recurrent inversion sprains were tested bilaterally. A custom-made apparatus provided a stress to the lateral ankle in a method that was similar to the inversion stress test. Two measures of laxity were used: maximum passive inversion range of motion and peak passive resistive torque. Differences between the involved and uninvolved ankles were determined using analysis of covariance procedures. There were no significant differences between involved and uninvolved ankles for maximum inversion range of motion and for peak passive resistive torque. Post hoc testing confirmed adequate statistical power. The results support previous investigations, which suggest that functional instability can exist in the absence of mechanical lateral ankle laxity.

Long-term detraining results for individuals 75 years and older are needed. The purpose of this study was to assess long-term detraining effects on quadriceps strength and functional mobility in nursing home residents. Ten women (X = 82.8 years) who completed a strength training program were reassessed 1 year later. Clinical methods were used to remeasure dynamic and isometric quadriceps strength and functional mobility. One repetition maximum quadriceps strength declined 68.3% (p < 0.05) from trained values. Isometric strength losses were 29.8% at 90 degrees (p < 0.05), 28.7% at 60 degrees (p < 0.05), and 24.4% at 20 degrees (p < 0.05) of knee flexion 1 year postexercise. Fast-paced walking, self-selected paced walking, and timed up and go speed decreased 28.6% (p < 0.05), 19.5% (p < 0.05), and 54.1% (not significant), respectively, from posttraining. One year vs. baseline, isometric strength decreased 0-14.3%, dynamic strength decreased 48.9%, and functional mobility declined 16.5-20.7% despite an intervening training program. An increased strength loss rate beyond the age of 80 years may be a major factor influencing functional independence.

The purpose of this study was to determine the effect of aging on the muscle length-tension relationship in the plantarflexor muscles of 10 subjects aged 20-30 yr (Mean = 23; 5 males, 5 females), 10 subjects aged 60-80 yr (Mean = 72.3; 5 males, 5 females), and 10 subjects over 80 yr (Mean = 84.1, 5 males, 5 females). Isometric twitch properties, maximum voluntary strength, passive tension, and range of motion were measured at five different joint angles [20 degrees dorsiflexion (DF), 10 degrees DF, 0 degree, 10 degrees plantarflexion (PF), and 20 degrees PF]. Active (evoked and voluntary) and passive torque production were maximal when the ankle was rotated into the DF positions for all three age groups, whereas the lowest values were recorded when the ankle was rotated into 20 degrees PF. Males were stronger than females at all joint angles (p < .01). Also, young adults were stronger than both elderly adult groups (p < .01). These results illustrate that despite the considerable age-associated loss in both voluntary and evoked strength in the plantarflexors, the optimal angle for torque production remains the same for younger and older adults.

The purpose was to investigate the effects of exercise velocity on stretch-shortening cycles of concentric (CONC) and eccentric (ECC) dorsiflexor(DF) and plantar flexor (PF) torque production in older adults. Twenty-two men and women volunteers ([horizontal bar over]x age = 74.8 ± 3.9 years) completed 2 weeks, 3 sessions/week, of DF and PF isokinetic exercise at 30, 90 and 180°/sec on a KIN COM. Isokinetic training involved one set of 6 maximum voluntary contractions (MVC)/session at the three velocities for CONC/ECC and ECC/CONC DF and PF exercise. Repeated measures analyses of variance were calculated to determine statistical significance. Baseline torque values prior to resistance training were not significantly different between CONC/ECC versus ECC/CONC ankle DF or PF. Post-training results demonstrated a significant increase (31.0%, p<.05) in DF ECC torque at 180°/sec when preceded by a CONC contraction. DF CONC torque was also significant at 180°/sec after training but decreased in value (24.4%, p<.05) when following an ECC contraction. No potentiation by contraction order for PF ECC or CONC torque at any velocity was found pre- or post-training. The decrease in CONC DF torque may be secondary to the fatiguing effects of preceding ECC contractions. The pre-shortened passive components before ECC DF contraction may be contributing to enhanced ECC torque during DF lengthening.

Faculty of Kinesiology and Dept. of Physical Therapy, University of Western Ontario, London, Ont., Canada.

BACKGROUND AND PURPOSE:The purpose of this study was to quantify several variables of ankle stiffness and dorsiflexion (DF) range of motion (ROM) in the casted (fractured) and noncasted ankles of humans after cast removal.SUBJECTS:Thirty subjects (mean age = 32.4 years, SD = 15.8) with malleolar ankle fractures were tested within 4 days of cast removal but before they began physical therapy.METHODS:A torque motor system generated torque-versus-displacement graphs by recording angular displacement and resistive torque during a 6 0/s passive cycling of the ankle from 10 degrees of plantar flexion to the limit of DF ROM: Maximum passive DF ROM, passive torque, and passive elastic stiffness at the neutral position and energy loss were measured. Testing was performed in the absence of triceps surae muscle electromyographic activity. For analysis, subjects were separated into two groups based on fracture severity.RESULTS:There was no difference in passive torque between the fractured ankles and the matched noncasted ankles. There was a small difference in passive elastic stiffness between the more severely fractured ankles and the matched noncasted ankles. The fractured ankles were different in terms of energy loss from the matched noncasted ankles. For maximum passive DF ROM, there was a large difference between the fractured ankles (more severe: mean = 4.4 degrees; less severe: mean = 6.8 degrees) and the matched noncasted ankles (more severe: mean = 15.1 degrees; less severe: mean = 19.1 degrees).CONCLUSION AND DISCUSSION:Altered length-tension relationships and neuromuscular mechanisms have been suggested to produce postimmobilization joint contractures. The results of this study on humans are consistent with both possibilities and support the theory that changes that occur during immobilization result in protection from overstretching of the fragile calf musculature after a period of ankle fixation. The time course of normalization of stretch reflexes warrants investigation.

Faculty of Kinesiology, and Dept. of Physical Therapy, University of Western Ontario, London, Ont., Canada.