Power and work produced in different leg muscle groups when rising from a chair

Clinimetric evaluation of five clinically feasible measures of the leg extensor muscle strength in neurological rehabilitation settings

A gold-standard clinical measure of leg muscle strength has not been established. Therefore, the aim of this study was to evaluate clinimetric properties of five clinically feasible measures of lower-limb extensor muscle strength in neurological rehabilitation settings. This was a cross-sectional observational study of 36 participants with leg weakness as a result of a neurological condition/injury. Participants were recruited across a range of walking abilities, from non- to independently ambulant. Each was assessed using each of the following five measures: manual muscle test (MMT), hand-held dynamometry (HHD), seated single leg press one repetition maximum (1RM), functional sit-to-stand (STS) test and seated single leg press measured with a load cell. Each clinical measure was evaluated for its discriminative ability, floor/ceiling effects, test-retest reliability and clinical utility. The load cell and HHD were the most discriminative of the tests and were also resistant to floor/ceiling effects; however, the load cell was superior to the HHD when compared for its clinical utility. The MMT/STS tests received perfect scores for clinical utility, although similar to the 1RM test, they were susceptible to floor and ceiling effects. The load cell leg press test was the only measure of lower limb strength to satisfy all four clinimetric properties. Implications for clinical practice include, firstly, that strength tests available to clinicians vary in their clinimetric properties. Secondly, the functional status of the person will determine selection of the best clinical strength test. And lastly, load cell device technology should be considered for clinical strength assessments.

Knee Exoskeleton Reduces Muscle Effort and Improves Balance During Sit-to-Stand Transitions After Stroke: A Case Study

After a stroke, the weight-bearing asymmetry often forces stroke survivors to compensate with overuse of the unaffected side muscles to stand up. Powered exoskeletons can address this problem by assisting the affected limb during sit-tostand transitions. However, there is currently no experimental evidence demonstrating the efficacy of this intervention with the target population. This study explores controlling a powered knee exoskeleton with EMG signals to assist a stroke patient during sit-to-stand transitions. Our results show decreased peak knee torques by 6.24% and 11.9% on their unaffected and affected sides, respectively, while wearing the exoskeleton. Additionally, the peak value of the EMG signal decreased by 29.3% and 21.9%, and the integrated EMG signal value decreased by 46.7% and 36.1% on their affected vastus medialis and lateralis while wearing the exoskeleton, respectively. Finally, our results indicate improved medial-lateral balance by 61.2%, 81.6%, and 70.0% based on the degree of asymmetry (DOA), the center of pressure (COP), and the center of mass (COM), respectively. These results support the efficacy of using powered exoskeletons for high-torque tasks such as sit-to-stand transitions with stroke survivors.

Physical Exercise Program on Fall Prevention Using Technological Interface: Pretest Study

Background

Prevention of falls among older adults has boosted the development of technological solutions, requiring testing in clinical contexts and robust studies that need prior validation of procedures and data collection tools.

Objective

The objectives of our study were to test the data collection procedure, train the team, and test the usability of the FallSensing Games app by older adults in a community setting.

Methods

This study was conducted as a pretest of a future pilot study. Older adults were recruited in a day care center, and several tests were applied. Physical exercise sessions were held using the interactive FallSensing Games app. Nurse training strategies was completed.

Results

A total of 11 older adults participated. The mean age was 75.08 (SD 3.80) years, mostly female (10/11, 91%) and with low (3-6 years) schooling (10/11, 91%). Clinically, the results show a group of older adults with comorbidities. Cognitive evaluation of the participants through the Mini Mental State Examination showed results with an average score of 25.64 (SD 3.5). Functional capacity assessed using the Lawton Instrumental Activities of Daily Living Scale (overall score from 0-23, with lower scores reflecting worse capacity to perform activities) showed impairment in different instrumental activities of daily living (average score 14.27). The data collection tool proved to enable easy interpretation; however, its structure needed small adjustments to facilitate the data collection process. Despite the length of the questionnaire, its implementation took an average of 21 minutes. For the assessment of the prevalence of fear of falling, the need to add a question was identified. The performance of functional tests under the guidance and presence of rehabilitation nurses ensured the safety of the participants. The interactive games were well accepted by the participants, and the physical exercises allowed data collection on the functionality of the older adults, such as the number of repetitions in the tests, range of movement (angle), duration of the movements, and execution of each cycle. Concerning the training of the nurses, it was crucial that they had experience with the platform, specifically the position of the chair facing the platform, the position of the feet, the posture of participants, and the use of sensors.

Conclusions

In the future pilot study, the researchers point out the need to design a study with mixed methods (quantitative and qualitative), thus enriching the study results.

An Individualized Exercise Intervention for People with Multiple Myeloma—Study Protocol of a Randomized Waitlist-Controlled Trial

People with multiple myeloma (MM) are second only to people with lung cancer for the poorest reported health-related quality of life (HRQoL) of all cancer types. Whether exercise can improve HRQoL in MM, where bone pain and lesions are common, requires investigation. This trial aims to evaluate the efficacy of an exercise intervention compared with control on HRQoL in people with MM. Following baseline testing, people with MM (n = 60) will be randomized to an exercise (EX) or waitlist control (WT) group. EX will complete 12-weeks of supervised (24 sessions) and unsupervised (12 sessions) individualized, modular multimodal exercise training. From weeks 12–52, EX continue unsupervised training thrice weekly, with one optional supervised group-based session weekly from weeks 12–24. The WT will be asked to maintain their current activity levels for the first 12-weeks, before completing the same protocol as EX for the following 52 weeks. Primary (patient-reported HRQoL) and secondary (bone health and pain, fatigue, cardiorespiratory fitness, muscle strength, body composition, disease response, and blood biomarkers) outcomes will be assessed at baseline, 12-, 24- and 52-weeks. Adverse events, attendance, and adherence will be recorded and cost-effectiveness analysis performed. The findings will inform whether exercise should be included as part of standard myeloma care to improve the health of this unique population.

Isometric knee extension test: A practical, repeatable, and suitable tool for lower-limb screening among institutionalized older adults

We aimed to analyze the isometric knee extension test (IKE) test in terms of i) intra- and inter-session repeatability, and ii) relationship with functional and body composition factors of sarcopenia among institutionalized older adults. Thirteen institutionalized older adults (age = 87 ± 10 years, body mass [BM] = 73.1 ± 10.9 kg, body mass index [BMI] = 28.5 ± 3.8 kg·m²) were recruited from a nursing home. Variability of maximal isometric force registered in three IKE trials performed on the same day was used to examine intra-session repeatability, whereas inter-session repeatability was analyzed by comparing maximal isometric force from two different days. Furthermore, functional (Handgrip, 6-m Gait Speed, Time Up and Go [TUG], and Sit-to-stand tests) and body composition (appendicular lean mass adjusted by BMI, ALM/BMI) evaluations were conducted. Statistics included the intraclass correlation coefficient (ICC) and the standard error of measurement (SEM), expressed in both absolute (N·kg^-1) and relative terms (coefficient of variation, CV = 100 × SEM / mean). High to very high intra-session repeatability was found for both the dominant and non-dominant legs (CV ≤ 6.0%, ICC ≥ 0.989). Similarly, both legs showed high inter-session repeatability (SEM ≤ 0.26 N·kg^-1, ICC ≥ 0.959). On the other hand, significant relationships were found between Dominant and Non-dominant IKE tests and 6-m Gait Speed (r = 0.77; r = 0.58), ALM/BMI (r = 0.62; r = 0.58), and Non-dominant Handgrip/BM (r = 0.60; r = 0.68). In addition, a significant association was found between Dominant IKE/BM and TUG (r = -0.74), as well as between Non-dominant IKE/BM and Dominant Handgrip/BM (r = 0.67). These findings suggest that the IKE test is a repeatable and suitable strategy for lower-limb screening in institutionalized older adults.

A Technological-Based Platform for Risk Assessment, Detection, and Prevention of Falls Among Home-Dwelling Older Adults: Protocol for a Quasi-Experimental Study

Background

According to the United Nations, it is estimated that by 2050, the number of people aged 80 years and older will have increased by 3 times. Increased longevity is often accompanied by structural and functional changes that occur throughout an individual’s lifespan. These changes are often aggravated by chronic comorbidities, adopted behaviors or lifestyles, and environmental exposure, among other factors. Some of the related outcomes are loss of muscle strength, decreased balance control, and mobility impairments, which are strongly associated with the occurrence of falls in the elderly. Despite the continued undervaluation of the importance of knowledge on fall prevention among the elderly population by primary care health professionals, several evidence-based (single or multifaceted) fall prevention programs such as the Otago Exercise Program (OEP) have demonstrated a significant reduction in the risk of falls and fall-related injuries in the elderly within community settings. Recent studies have strived to integrate technology into physical exercise programs, which is effective for adherence and overcoming barriers to exercise, as well as improving physical functioning.

Objective

This study aims to assess the impact of the OEP on the functionality of home-dwelling elderly using a common technological platform. Particularly, the impact on muscle strength, balance, mobility, risk of falling, the perception of fear of falling, and the perception of the elderly regarding the ease of use of technology are being examined in this study.

Methods

A quasi-experimental study (before and after; single group) will be conducted with male and female participants aged 65 years or older living at home in the district of Porto. Participants will be recruited through the network COLABORAR, with a minimum of 30 participants meeting the study inclusion and exclusion criteria. All participants will sign informed consent forms. The data collection instrument consists of sociodemographic and clinical variables (self-reported), functional evaluation variables, and environmental risk variables. The data collection tool integrates primary and secondary outcome variables. The primary outcome is gait (timed-up and go test; normal step). The secondary outcome variables are lower limb strength and muscle resistance (30-second chair stand test), balance (4-stage balance test), frequency of falls, functional capacity (Lawton and Brody - Portuguese version), fear of falling (Falls Efficacy Scale International - Portuguese version), usability of the technology (System Usability Scale - Portuguese version), and environmental risk variables (home fall prevention checklist for older adults). Technological solutions, such as the FallSensing Home application and Kallisto wearable device, will be used, which will allow the detection and prevention of falls. The intervention is characterized by conducting the OEP through a common technological platform 3 times a week for 8 weeks. Throughout these weeks, the participants will be followed up in person or by telephone contact by the rehabilitation nurse. Considering the COVID-19 outbreak, all guidelines from the National Health Service will be followed. The project was funded by InnoStars, in collaboration with the Local EIT Health Regional Innovation Scheme Hub of the University of Porto.

Results

This study was approved on October 9, 2020 by the Ethics Committee of Escola Superior de Enfermagem do Porto (ESEP). The recruitment process was meant to start in October, but due to the COVID-19 pandemic, it was suspended. We expect to restart the study by the beginning of the third quarter of 2021.

Conclusions

The findings of this study protocol will contribute to the design and development of future robust studies for technological tests in a clinical context.

Trial Registration

ISRCTN 15895163; https://www.isrctn.com/ISRCTN15895163

International Registered Report Identifier (IRRID)

PRR1-10.2196/25781

Age-Related Differences in Hip Flexion Maximal and Rapid Strength and Rectus Femoris Muscle Size and Composition

This study aimed to examine the effects of age on hip flexion maximal and rapid strength and rectus femoris (RF) muscle size and composition in men. Fifteen young (25 [3] y) and 15 older (73 [4] y) men performed isometric hip flexion contractions to examine peak torque and absolute and normalized rate of torque development (RTD) at time intervals of 0 to 100 and 100 to 200 milliseconds. Ultrasonography was used to examine RF muscle cross-sectional area and echo intensity. Peak torque, absolute RTD at 0 to 100 milliseconds, and absolute and normalized RTD at 100 to 200 milliseconds were significantly lower (P = .004-.045) in the old compared with the young men. The older men exhibited lower cross-sectional area (P = .015) and higher echo intensity (P = .007) than the young men. Moreover, there were positive relationships between cross-sectional area and absolute RTD at 0 to 100 milliseconds (r = .400) and absolute RTD at 100 to 200 milliseconds (r = .450) and negative relationships between echo intensity and absolute RTD at 100 to 200 milliseconds (r = -.457) and normalized RTD at 100 to 200 milliseconds (r = -.373). These findings indicate that hip flexion maximal and rapid strength and RF muscle size and composition decrease in old age. The relationships observed between ultrasound-derived RF parameters and measurements of RTD suggest that these age-related declines in muscle size and composition may be relevant to hip flexion rapid torque production.

Benefits of Resistance Training in Early and Late Stages of Frailty and Sarcopenia: A Systematic Review and Meta-Analysis of Randomized Controlled Studies

Sarcopenia and frailty are age-related syndromes with negative effects on the quality of life of older people and on public health costs. Although extensive research has been carried out on the effects of physical exercise and physical syndromes, there is a knowledge gap when it comes to the effect of resistance training on muscular strength, physical performance, and body composition at early (prevention) and late (treatment) stages in both syndromes combined. We conducted this systematic review and meta-analysis (CRD42019138253) to gather the evidence of randomized controlled trials examining the effects of resistance training programs lasting ≥8 weeks on strength, physical function, and body composition of adults ≥65 years old diagnosed with pre-sarcopenia, sarcopenia, pre-frailty, or frailty. A search from the earliest record up to and including December 2020 was carried out using the PubMed, Scopus, Web of Science, and Cochrane Library databases. A total of 25 studies (n = 2267 participants) were included. Meta-analysis showed significant changes in favour of resistance training for handgrip (ES = 0.51, p = 0.001) and lower-limb strength (ES = 0.93, p < 0.001), agility (ES = 0.78, p = 0.003), gait speed (ES = 0.75, p < 0.001), postural stability (ES = 0.68, p = 0.007), functional performance (ES = 0.76, p < 0.001), fat mass (ES = 0.41, p = 0.001), and muscle mass (ES = 0.29, p = 0.002). Resistance training during early stages had positive effects in all variables during early stages (ES > 0.12), being particularly effective in improving gait speed (ES = 0.63, p = 0.016) and functional strength (ES = 0.53, p = 0.011). Based on these results, resistance training should be considered as a highly effective preventive strategy to delay and attenuate the negative effects of sarcopenia and frailty in both early and late stages.

Lumbar spine loads are reduced for activities of daily living when using a braced arm-to-thigh technique

PURPOSE

To evaluate the effect of the braced arm-to-thigh technique (BATT) (versus self-selected techniques) on three-dimensional trunk kinematics and spinal loads for three common activities of daily living (ADLs) simulated in the laboratory: weeding (gardening), reaching for an object in a low cupboard, and car egress using the two-legs out technique.

METHODS

Ten young healthy males performed each task using a self-selected technique, and then using the BATT. The pulling action of weeding was simulated using a magnet placed on a steel plate. Cupboard and car egress tasks were simulated using custom apparatus representing the dimensions of a kitchen cabinet and a medium-sized Australian car, respectively. Three-dimensional trunk kinematics and L4/L5 spinal loads were estimated using the Lifting Full-Body OpenSim model and compared between techniques. Paired t-tests were used to compare peak values between methods (self-selected vs BATT).

RESULTS

The BATT significantly reduced peak extension moments (13-51%), and both compression (27-45%) and shear forces (31-62%) at L4/L5, compared to self-selected techniques for all three tasks (p < 0.05). Lateral bending angles increased with the BATT for weeding and cupboard tasks, but these changes were expected as the BATT inherently introduces asymmetric trunk motion.

CONCLUSION

The BATT substantially reduced L4/L5 extension moments, and L4/L5 compression and shear forces, compared to self-selected methods, for three ADLs, in a small cohort of ten young healthy males without prior history of back pain. These study findings can be used to inform safe procedures for these three ADLs, as the results are considered representative of a mature population.

External Validation Of The Updated ADO Score In COPD Patients From The Birmingham COPD Cohort

Background

Reviews suggest that the ADO score is the most discriminatory prognostic score for predicting mortality among chronic obstructive pulmonary disease (COPD) patients, but a full evaluation and external validation within primary care settings is critical before implementation.

Objectives

To validate the ADO score in prevalent and screen-detected primary care COPD cases at 3 years and at shorter time periods.

Patients and methods

One thousand eight hundred and ninety-two COPD cases were recruited between 2012 and 2014 from 71 United Kingdom general practices as part of the Birmingham COPD Cohort study. Cases were either on the practice COPD register or screen-detected. We validated the ADO score for predicting 3-year mortality with 1-year and 2-year mortality as secondary endpoints using discrimination (area-under-the-curve (AUC)) and calibration plots.

Results

One hundred and fifty-four deaths occurred within 3 years. The ADO score was discriminatory for predicting 3-year mortality (AUC= 0.74; 95% CI: 0.69–0.79). Similar performance was found for 1- (AUC= 0.73; 0.66–0.80) and 2-year mortality (0.72; 0.67–0.76). The ADO score showed reasonable calibration for predicting 3-year mortality (calibration slope 0.95; 0.70–1.19) but over-predicted in cases with higher predicted risks of mortality at 1 (0.79; 0.45–1.13) and 2-year (0.79; 0.57–1.01) mortality.

Discussion

The ADO score showed promising discrimination in predicting 3-year mortality in a primary care population including screen-detected cases. It may need to be recalibrated if it is used to provide risk predictions for 1- or 2-year mortality since, in these time-periods, over-prediction was evident, especially in cases with higher predicted mortality risks.

A body-fixed-sensor-based analysis of stair ascent and sit-to-stand to detect age-related differences in leg-extensor power

Human ageing is accompanied by a progressive decline in leg-extensor power (LEP). LEP is typically measured with specialized and expensive equipment, which limits the large-scale applicability. Previously, sensor-based trunk kinematics have been used to estimate the vertical power required to elevate the body’s center of mass during functional tests, but the link with LEP and age remains to be investigated. Therefore, we investigated whether a body-fixed sensor-based analysis of power during stair ascent (SA) and sit-to-stand (STS) is positively related to LEP and whether its ability to detect age-related declines is similar. In addition, the effect of load during SA and STS was investigated. 98 adults (20–70 years) performed a leg press to assess LEP, SA and 5-repetition STS tests. In SA and STS, two conditions were tested: unloaded and loaded (+10% body mass). An inertial measurement unit was used to analyze (sub)-durations and vertical power. SA and STS power were more related to LEP than duration parameters (i.e. 0.80–0.81 for power and -0.41 –-0.66 for duration parameters, p < 0.05). The average annual age-related percent change was higher in SA power (-1.38%) than in LEP (-0.86%) and STS power (-0.38%) (p < 0.05). Age explained 29% in SA power (p < 0.001), as opposed to 14% in LEP (p < 0.001) and a non-significant 2% in STS power (p = 0.102). The addition of 10% load did not influence the age-related decline of SA and STS power nor the relationship with LEP. These results demonstrate the potential of SA tests to detect age-related deterioration in neuromuscular function. SA seems more sensitive to detect age-related changes than LEP, probably because of the additional balance component and plantar- and dorsiflexor activity. On the contrary, STS is less sensitive to age-related changes because of a ceiling effect in well-functioning adults.

The influence of knee extensor fatigue on lower extremity muscle activity during chair rise in young and older adults

PURPOSE

The purpose of this investigation was to evaluate alterations in muscular effort and temporal characteristics of their activity during the sit-to-stand (STS) due to isolated fatiguing of the knee extensors, as indicated by declines in torque output.

METHODS

Surface electromyography of the lower extremity was recorded in healthy young (n = 11) and older (n = 11) adults as they ascended from a seated position, before and after dynamic knee extension exercise.

RESULTS

Knee extensor fatigue caused significant increases in soleus, gastrocnemius, and gluteus maximus relative effort (%MVC) in both age groups during the STS task. Rectus femoris %MVCs in both young and older adults significantly increased to similar extents throughout the STS movement, whereas vastus lateralis amplitudes only increased in preparation for seat-off. Muscle temporal characteristics appeared to generally be invariant with fatigue, except for earlier activation onset for the ankle musculature in older adult participants.

CONCLUSIONS

These findings demonstrate that isolated knee extension fatiguing exercise caused compensatory changes in muscle activation patterns and increased reliance of non-fatigued muscles at the ankle and hip as well as increased activity of synergist muscles during the STS. Moreover, this occurred to similar extents in older adults who had lower knee extensor strengths and greater quadriceps %MVCs in comparison to their younger counterparts, regardless of fatigue condition.

The role of thigh muscular efforts in limiting sit-to-stand capacity in healthy young and older adults

Aging is associated with an unavoidable decline in muscle mass, known as sarcopenia, leading to neuromuscular declines, muscle weakness, and subsequent disability. One particular measure utilized by rehabilitative professionals in evaluating functional declines in older persons is sit-to-stand (STS) capacity. The purpose of this investigation was to determine the role of activation intensity requirements of the thigh musculature in limiting a multi-joint STS endurance task. To do so, surface EMG signals of the quadriceps femoris (QF) and hamstrings (biceps femoris; BF) and their co-activation ratios (H:Q) were collected in young (18-35 years; n = 12) and older (60-75 years; n = 12) adult participants who repeatedly stood from a seated position until exhaustion. QF %MVIC was the sole predictor of total STS task times, as those who required the highest quadriceps efforts had the shortest task times. Moreover, older adult participants had significantly higher starting QF %MVIC as well as shorter task times. Interestingly, the H:Q ratio was not a significant predictor of STS capacities, nor did it differ between age groups or with fatigue. Results indicate that strengthening of the quadriceps to elevate or maintain strength reserves may improve an older adult's ability to perform multi-joint tasks repetitively throughout the day.

Design and characterization of a torque-controllable actuator for knee assistance during sit-to-stand

Individuals with post-stroke hemiparesis often have difficulty standing out of a chair. One way to potentially improve sit-to-stand is to provide knee extension assistance using a powered knee exoskeleton. An exoskeleton providing unilateral, partial assistance during sit-to-stand would need to be torque-controllable. There are no knee exoskeletons on the market suitable for conducting experiments assisting stroke patients with sit-to-stand, so to enable such experiments a research device was developed. The purpose of this report is to present the design of a novel knee exoskeleton actuator that uses a fiberglass leaf spring in series to improve torque-controllability, and present a characterization of the actuator performance. The actuator is capable of the required torque and speed for sit-to-stand, has high bandwidth (25 Hz), low output impedance at low frequencies (<;0.5 Nm), and excellent torque tracking. An orthotic brace built upon this actuator will enable an in-depth study on the biomechanical effects of providing stroke subjects with knee extension assistance during sit-to-stand.

Effectiveness of the Easy-Up Handle in acute rehabilitation

Objective: The ability to attain standing without assistance is important to independent functioning. The objectives of this study, therefore, were to: (1) determine the effectiveness of the Easy-Up Handle for enabling otherwise dependent patients to attain standing from an armless chair and (2) establish whether knee extension force played a role in such effectiveness.

Design: Cross-sectional descriptive study and explicatory experiment.

Setting: Acute rehabilitation unit.

Subjects: A subset ( n = 26) of 107 primarily elderly patients described in a previous study. The subjects were selected because of their inability to stand from an armless chair, even when using their upper limbs.

Main measures: The ability to stand from the same chair when using an Easy-Up Handle. Hand-held dynamometer measures of the combined strength of the lower extremities.

Results: Eight of 26 otherwise dependent patients were able to stand up independently with the Easy-Up Handle. Whether or not they were able to attain standing with the Easy-Up Handle was predicted by their combined knee extension force and by their combined force normalized against body weight. The Pearson correlations between stand-up independence (yes, no) and the forces were 0.496 and 0.543, respectively.

Conclusions: The Easy-Up Handle can facilitate independence in chair rise for some patients otherwise unable to stand from sitting. Even with the Easy-Up Handle, however, a threshold of knee extension force is required.

The effect of total hip and hip resurfacing arthroplasty on vertical ground reaction force and impulse symmetry during a sit-to-stand task

BACKGROUND

The aim of this study was to determine the influence of total hip arthroplasty and hip resurfacing arthroplasty on limb loading symmetry before, and after, hip reconstruction surgery during a sit-to-stand task.

METHODS

Fourteen patients were recruited that were about to receive either a total hip prosthesis (n=7) or a hip resurfacing prosthesis (n=7), as well as matched controls. Patients performed a sit-to-stand movement before, 3 months after, and 12 months after surgery. Peak vertical ground reaction force and impulse were measured for each leg, from which ground reaction force and impulse symmetry ratios were calculated.

FINDINGS

Before surgery, hip resurfacing patients showed a small asymmetry which was not different to normal for ground reaction force (0.88(0.28) vs. 1.00(0.11); p=0.311) or impulse (0.87(0.29) vs. 0.99(0.09); p=0.324) symmetry ratios. Total hip patients offloaded their affected hip by 30% in terms of impulse symmetry ratio (0.71(0.36) vs. 0.99(0.23); p=0.018). At 3 months following surgery asymmetries were seen that were different to normal in both hip resurfacing patients for ground reaction force (0.77(0.16); p=0.007), and total hip patients for ground reaction force (0.70(0.15); p=0.018) and impulse (0.72(0.16); p=0.011) symmetry ratios. By 12 months after surgery total hip patients regained a symmetrical loading pattern for both ground reaction force (0.95(0.06); p=0.676) and impulse (1.00(0.06); p=0.702) symmetry ratios. Hip resurfacing patients, however, performed the task by overloading their operated hip, with impulse symmetry ratio being larger than normal (1.16(0.16); p=0.035).

INTERPRETATION

Physiotherapists should appreciate the need for early recovery of limb loading symmetry as well as subsequent differences in the responses observed with different prostheses.

Discriminative ability of the three functional tests in independent ambulatory patients with spinal cord injury who walked with and without ambulatory assistive devices

BACKGROUND/OBJECTIVES

Many persons with spinal cord injury (SCI) require an ambulatory assistive device (AAD). An effective monitoring method enables the use of an appropriate AAD and promotes levels of independence for patients. This study investigated the discriminative ability of the three-functional tools relating to walking ability, including the 10-meter walk test (10MWT), the five times sit-to-stand test (FTSST), and the timed up and go test (TUGT), in independent ambulatory persons with SCI who walked with walker, crutches, cane, and non-AAD.

METHODS

Eighty-five persons with SCI who could perform sit-to-stand and walk independently at least 50 m were cross-sectionally assessed for their functional ability using the 10MWT, FTSST, and TUGT.

RESULTS

The findings for persons not using AADs were significantly better than the other groups for every test (P < 0.001). In addition, persons who walked with cane were significantly different from those who used walkers (P < 0.001) but there were no significant differences between persons who used walker and crutches for every test (P > 0.05).

CONCLUSION

The findings supported the discriminative validity of the tools, allowing them to indicate functional changes in persons with SCI who walk with different AADs. However, the non-significant differences between subjects who used a walker and crutches may relate to the method of subject arrangement and inclusion criteria that recruit subjects with rather good walking capability and lower limb function. The findings may also suggest the use of the sit-to-stand maneuver as a simple screening tool for walking advancement of walker users, pending further investigation.

Test-retest reliability of innovated strength tests for hip muscles

The burden of hip muscles weakness and its relation to other impairments has been well documented. It is therefore a pre-requisite to have a reliable method for clinical assessment of hip muscles function allowing the design and implementation of a proper strengthening program. Motor-driven dynamometry has been widely accepted as the gold-standard for lower limb muscle strength assessment but is mainly related to the knee joint. Studies focusing on the hip joint are less exhaustive and somewhat discrepant with regard to optimal participants position, consequently influencing outcome measures. Thus, we aimed to develop a standardized test setup for the assessment of hip muscles strength, i.e. flexors/extensors and abductors/adductors, with improved participant stability and to define its psychometric characteristics. Eighteen participants performed unilateral isokinetic and isometric contractions of the hip muscles in the sagittal and coronal plane at two separate occasions. Peak torque and normalized peak torque were measured for each contraction. Relative and absolute measures of reliability were calculated using the intraclass correlation coefficient and standard error of measurement, respectively. Results from this study revealed higher levels of between-day reliability of isokinetic/isometric hip abduction/flexion peak torque compared to existing literature. The least reliable measures were found for hip extension and adduction, which could be explained by a less efficient stabilization technique. Our study additionally provided a first set of reference normalized data which can be used in future research.

Effects of robotic knee exoskeleton on human energy expenditure

A number of studies discuss the design and control of various exoskeleton mechanisms, yet relatively few address the effect on the energy expenditure of the user. In this paper, we discuss the effect of a performance augmenting exoskeleton on the metabolic cost of an able-bodied user/pilot during periodic squatting. We investigated whether an exoskeleton device will significantly reduce the metabolic cost and what is the influence of the chosen device control strategy. By measuring oxygen consumption, minute ventilation, heart rate, blood oxygenation, and muscle EMG during 5-min squatting series, at one squat every 2 s, we show the effects of using a prototype robotic knee exoskeleton under three different noninvasive control approaches: gravity compensation approach, position-based approach, and a novel oscillator-based approach. The latter proposes a novel control that ensures synchronization of the device and the user. Statistically significant decrease in physiological responses can be observed when using the robotic knee exoskeleton under gravity compensation and oscillator-based control. On the other hand, the effects of position-based control were not significant in all parameters although all approaches significantly reduced the energy expenditure during squatting.

Association between chair stand strategy and mobility limitations in older adults with symptomatic knee osteoarthritis

OBJECTIVE

To determine which lower limb strength and joint kinetic and kinematic parameters distinguish sit-to-stand (STS) performance of older adults with symptomatic knee osteoarthritis (OA) with higher and lower chair stand time.

DESIGN

Cross-sectional.

SETTING

Motion analysis laboratory.

PARTICIPANTS

Individuals (N=49; 26 men, 23 women) aged 50 to 79 years (mean ± SD age, 64.7±8.1y) with radiographic knee OA and daily symptoms, stratified by chair stand times.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Lower limb strength and STS strategy.

RESULTS

The chair stand times (mean ± SD) in the high-, moderate-, and low-functioning groups in men were 6.5±0.7, 8.6±0.7, and 11.5±1.3 seconds, respectively, and in women were 7.6±1.2, 10.0±0.5, and 12.8±1.8 seconds, respectively. Chair stand time (P=.0391) and all measures of lower limb strength (all P<.0001) differed by sex. In men, no strength measure differed between groups, whereas in women hip abductor strength on the more affected side differed between groups. In men, sagittal hip range of motion (ROM) (P=.0122) differed between groups, and there was a trend toward a difference in sagittal knee power (P=.0501) during STS, while in women only sagittal knee ROM (P=.0392) differed between groups.

CONCLUSIONS

Higher- and lower-functioning adults with symptomatic knee OA appear to use different strategies when standing from a chair. Higher-functioning men flexed more at the hip and produced greater knee power than lower-functioning men. Higher-functioning women used less knee flexion than lower-functioning women. Since STS is an important mobility task, these parameters may serve as foci for rehabilitation aimed at reducing mobility limitations.

The sit-to-stand movement: differences in performance between patients after primary total hip arthroplasty and revision total hip arthroplasty with acetabular bone impaction grafting

BACKGROUND

Little is known about the functional performance of patients after revision total hip arthroplasty with major acetabular bone impaction grafting. In general, these patients are assumed to perform worse due to a more advanced stage of periarticular tissue degeneration and multiple surgeries compared with patients with primary total hip arthroplasty (THA).

OBJECTIVE

The main purpose of this study was to quantify the differences in performance of the sit-to-stand (STS) movement between patients with primary THA and patients with revision THA.

DESIGN AND METHODS

In this study, the STS movement was analyzed kinematically (knee and hip angular extension velocity) and kinetically (loading symmetry ratio). Ten patients after primary THA and 10 patients after revision THA with acetabular bone impaction grafting were compared using these 3 rising parameters.

RESULTS

The patients with revision THA performed the STS movement comparably to the patients with primary THA; there were no differences in knee and hip velocity or leg asymmetry during rising.

LIMITATIONS

The study focused only on kinetic and kinematic aspects, and only patients who were satisfied with their THA were involved.

CONCLUSIONS

This study showed that patients after a revision THA with acetabular bone impaction grafting and cement did not perform the STS movement differently, either kinematically or kinetically, compared with patients with a primary THA.

Sit-to-stand test: Performance and determinants across the age-span

Although the validity of the sit-to-stand (STS) test as a measure of lower limb strength has been questioned, it is widely used as such among older adults. The purposes of this study were: 1) to describe five-repetition STS test (FRSTST) performance (time) by adolescents and adults and 2) to determine the relationship of isometric knee extension strength (force and torque), age, gender, weight, and stature with that performance. Participants were 111 female and 70 male (14-85 years) community-dwelling enrollees in the NIH Toolbox Assessment of Neurological and Behavioral Function. The FRSTST was conducted using a standard armless chair. Knee extension force was measured using a belt-stabilized hand-held dynamometer; knee extension torque was measured using a Biodex dynamometer. The mean times for the FRSTST ranged from 6.0 sec (20-29 years) to 10.8 sec (80-85 years). For both the entire sample and a sub-sample of participants 50-85 years, knee extension strength (r = -0.388 to -0.634), age (r = 0.561 and 0.466), and gender (r = 0.182 and 0.276) were correlated significantly with FRSTST times. In all multiple regression models, knee extension strength provided the best explanation of FRSTST performance, but age contributed as well. Bodyweight and stature were less consistent in explaining FRSTST performance. Gender did not add to the explanation of FRSTST performance. Our findings suggest, therefore, that FRSTST time reflects lower limb strength, but that performance should be interpreted in light of age and other factors.

Evaluation of sit-to-stand motion using a pressure distribution measurement system--effect of differences in seat hardness on sit-to-stand motion

PURPOSE

This study examined differences between standing from an ordinary seat and standing from a low-repulsion mat using a pressure distribution measurement system (BIG-MAT) and identified parameters to determine sit-to-stand (STS) motion difficulty.

METHOD

Ten healthy male volunteers (aged 30-38 years) participated. During STS motion from an ordinary seat and from a low-repulsion urethane mat, plantar surface pressure changes of both feet and the centre of pressure (COP) trajectory were recorded for 7  s. This series of tests was performed four times in each subject. Left and right pressure changes and COP changes were evaluated. Differences in the measurements between the low-repulsion mat and the ordinary seat were compared using the paired t-test.

RESULTS

COP changes were similar to those previously reported. Time from hindfoot peak to forefoot peak was significantly shorter with the ordinary chair than with the mat (p < 0.05). Percent change in forefoot pressure at forefoot peak and hindfoot peak (p < 0.01) and percent change in forefoot pressure at forefoot peak and stabilisation (p < 0.05) were significantly different.

CONCLUSIONS

Time from hindfoot peak to forefoot peak and percent change in forefoot pressure at forefoot peak and hindfoot peak were the best indicators of STS motion difficulty.

Sit-to-stand movement as a performance-based measure for patients with total knee arthroplasty

BACKGROUND

Functional recovery of patients after a total knee arthroplasty (TKA) usually is measured with questionnaires. However, these self-report measures assess the patient's perspective on his or her ability to perform a task. Performance-based tests are needed to assess the patient's actual ability to perform a task.

OBJECTIVE

The main purpose of this study was to quantify improvement in performance of the sit-to-stand movement of patients with a TKA.

DESIGN AND METHODS

In this prospective study of 16 patients with end-stage knee osteoarthritis followed by a TKA, the maximal knee angular extension velocity and amount of unloading (shifting weight) of the affected leg during the sit-to-stand movement and the visual analog scale score for pain were assessed preoperatively and 6 months and 1 year postoperatively. These data were compared with data for a control group of individuals who were healthy (n=27).

RESULTS

Before surgery, the participants in the TKA group unloaded their affected leg, but within 6 months after implantation, the affected leg was almost fully loaded again and comparable to the loading symmetry ratio of the control group. Furthermore, knee extension velocity also had increased, but remained lower than that of the control group. The changes in knee extension velocity took place during the first 6 months, after which a plateau was visible. Limitations A potential limitation of the study design was that the patients were not perfectly matched with the control subjects.

CONCLUSIONS

Implantation of a total knee prosthesis partly improved performance of the sit-to-stand movement. Participants in the TKA group could fully load their operated leg, but they could not generate enough knee angular velocity during rising compared with the control group.

Force-velocity, force-power relationships of bilateral and unilateral leg multi-joint movements in young and elderly women

The present study investigated force-velocity and force-power relationships of bilateral and unilateral knee-hip extension movement in young and elderly women. Twelve healthy young (age, 19-31 yr) and 12 healthy elderly (age, 60-82 yr) women performed bilateral and unilateral knee-hip extension movements on the dynamometer against loads controlled by the servo system. Under the isotonic force condition, force-velocity relationships were measured. The maximum isometric force (F(max)), unloaded velocity (V(max)) and power output (P(max)) of the movements were calculated from extrapolating force-velocity and force-power relationships. F(max) and P(max) of bilateral and unilateral knee-hip extension movements were 20-30% lower in elderly than in young women. On the other hand, there were no significant differences in V(max) between young and elderly women and between bilateral and unilateral movements. Bilateral deficit was larger as the generation of force was larger in both young and elderly women. Also, bilateral deficit of F(max) and P(max) were not different between young and elderly women. The results were that lower maximum power output of bilateral and unilateral leg multi-joint movements in elderly women did not depend on the intrinsic shortening velocity of muscle action, but largely on reduction in force generating capacity. This suggests the importance of preventing a loss of force generating capacity of muscles during leg multi-joint movements in elderly women.

Intrarater test-retest reliability of hip range of motion and hip muscle strength measurements in persons with hip osteoarthritis

OBJECTIVE

To examine the relative and absolute intrarater test-retest reliability of muscle strength and range of motion (ROM) measurements of the hip performed in people with hip osteoarthritis.

DESIGN

Repeated measures.

SETTING

Human movement laboratory of a university.

PARTICIPANTS

Participants (N=22; 10 men, 12 women; age range, 50-84y) with hip osteoarthritis.

INTERVENTIONS

On 2 separate occasions, at least 1 week apart, isometric torque measurements were obtained from the hip rotators, flexors, abductors, and extensors. Passive ROMs in hip rotation, flexion, abduction, and extension were also determined.

MAIN OUTCOME MEASURES

Relative reliability was estimated using the intraclass correlation coefficient, model 2,2 (ICC(2,2)). Absolute reliability was estimated using the coefficient of variation (CV) and the standard error (SE) of measurement.

RESULTS

For measurements of muscle strength, ICC(2,2) ranged from .84 to .97, and the CV ranged from 8% to 15.7%. Hip extensors and internal and external rotators showed high ICC(2,2) (>.96) and low CV (<9.8%); hip abductors showed the lowest ICC(2,2) (.84) and the highest CV (15.7%). For ROM measurements, ICC(2,2) ranged from .86 to .97 and SE ranged from 3.1 degrees to 4.7 degrees . Hip flexion ROM showed the highest ICC(2,2) (.97) and an SE of 3.5 degrees ; hip extension ROM showed the lowest ICC(2,2) (.86) and the highest SE (4.7 degrees ).

CONCLUSIONS

Strength and ROM testing of the hip in people with hip osteoarthritis can be performed with good to excellent reliability.

Relationships among impairments in lower-extremity strength and power, functional limitations, and disability in older adults

BACKGROUND AND PURPOSE

During the aging process, older adults may experience a loss of strength and power, which then may lead to functional limitations and disability. The purpose of this study was to examine how impairments in lower-extremity strength and power are related to functional limitations and disability in community-dwelling older adults.

SUBJECTS

Thirty older adults (age [X+/-SD], 77.3+/-7.0 years; 25 women and 5 men) with mild to moderate functional limitations participated in this study.

METHODS

Lower-extremity strength, peak power, power at a low relative intensity, and power at a high relative intensity were measured with a pneumatic resistance leg press. Functional limitations and disability were assessed with the Short Physical Performance Battery (SPPB), the Six-Minute Walk Test (SMWT), and the Late Life Function and Disability Instrument (LLFDI).

RESULTS

All measures of strength and power were related to functional limitations. Peak power demonstrated the strongest relationships with SMWT, the SPPB gait speed subscale, and the LLFDI functional limitation component. Power at a high relative intensity demonstrated the strongest relationships to the SPPB total score and the SPPB sit-to-stand subscale score. All measures of strength and power were indirectly related to the LLFDI disability component.

DISCUSSION AND CONCLUSION

Older adults should focus on increasing and maintaining lower-extremity strength and power across a range of intensities in order to decrease functional limitations and disability.

Hip, thigh and calf muscle atrophy and bone loss after 5-week bedrest inactivity

Unloaded inactivity induces atrophy and functional deconditioning of skeletal muscle, especially in the lower extremities. Information is scarce, however, regarding the effect of unloaded inactivity on muscle size and function about the hip. Regional bone loss has been demonstrated in hips and knees of elderly orthopaedic patients, as quantified by computerized tomography (CT). This method remains to be validated in healthy individuals rendered inactive, including real or simulated weightlessness. In this study, ten healthy males were subjected to 5 weeks of experimental bedrest and five matched individuals served as ambulatory controls. Maximum voluntary isometric hip and knee extension force were measured using the strain gauge technique. Cross-sectional area (CSA) of hip, thigh and calf muscles, and radiological density (RD) of the proximal tibial bone were measured using CT. Bedrest decreased (P < 0.05) average (SD) muscle strength by 20 (8)% in knee extension, and by 22 (12)% in hip extension. Bedrest induced atrophy (P < 0.05) of extensor muscles in the gluteal region, thigh and calf, ranging from 2 to 12%. Atrophy was more pronounced in the knee extensors [9 (4)%] and ankle plantar flexors [12 (3)%] than in the gluteal extensor muscles [2 (2)%]. Bone density of the proximal tibia decreased (P < 0.05) by 3 (2)% during bedrest. Control subjects did not show any temporal changes in muscle or bone indices (P > 0.05), when examined at similar time intervals. The present findings of a substantial loss in hip extensor strength and a smaller, yet significant atrophy of these muscles, demonstrate that hip muscle deconditioning accompanies losses in thigh and calf muscle mass after bedrest. This suggests that comprehensive quantitative studies on impaired locomotor function after inactivity should include all joints of the lower extremity. Our results also demonstrate that a decreased RD, indicating bone mineral loss, can be shown already after 5 weeks of unloaded bedrest, using a standard CT technique.

Reliability of a New Instrument for Measuring Maximum Rising Strength

OBJECTIVE

To assess the intrarater test-retest reliability of a newly developed instrument for measuring maximum rising strength (MRS) in comparison with that of maximum knee extension strength (KES).

DESIGN

Three replications of isometric MRS and KES were measured on three test occasions separated by 1 wk in 97 healthy men and women aged 23-90. MRS was measured in seated subjects using a dynamometer fixed on the ground and connected by an adjustable nonelastic cord to a padded belt.

RESULTS

The intraclass coefficients (ICCs) of MRS were 0.92 and 0.93 at 60 and 70 degrees of knee flexion, respectively, and 0.98 when the mean of three highest peak values of MRS at 60 degrees and the three highest peak values at 70 degrees knee flexion on each session were considered vs. 0.95 for KES. A significant increase in MRS and KES strength was found between the first and the third sessions (+7 to 8%)(P < 0.001). No side effects of strength measurements were noticed.

CONCLUSION

Despite a significant learning effect, MRS measurement is reliable in men and women of a wide range of ages. Whether this instrument will be useful for targeting individuals with early sit-to-stand difficulties requires further investigation.

Test methods to detect hip and knee muscle weakness and gait disturbance in patients with hip osteoarthritis

OBJECTIVE

To evaluate test methods for hip and knee muscle weakness and gait disturbance.

DESIGN

Test-retest.

SETTING

Orthopedic university clinic.

PARTICIPANTS

Ten young (age, 36+/-6 y) and 13 elderly (age, 69+/-8 y) healthy volunteers and 11 patients (age, 69+/-8 y) with unilateral hip osteoarthritis (OA) were tested for muscular strength. Twenty-five volunteers (age, 42+/-14 y) underwent gait analysis.

INTERVENTIONS

A dynamometer assessing maximal voluntary isometric force of hip and knee muscles and an optosensor walkway detecting limp were developed. Tests evaluated reproducibility and tolerance in patients with OA and elderly subjects.

MAIN OUTCOME MEASURES

Relative coefficient of variation (CV%) and force (in newtons).

RESULTS

CV% for unilateral strength measurements ranged from 7% to 12% for specific muscle groups. CV% for gait parameters ranged from 4% to 8%, except for the double-support phase. Tests were well tolerated, and no patient had to discontinue because of fatigue. Differences related to sex, age, and disease were detected.

CONCLUSIONS

Our dynamometer system provides reliable measurements of hip and knee muscle strength in young and old people, and variation is comparable to previous data. Our photocell technique for gait analysis is reliable in people with normal gait. Both methods are attractive because they are affordable, nonstationary, and easy to use.

Estrogen replacement, muscle composition, and physical function: The Health ABC Study

PURPOSE

Although the beneficial effects of estrogen use on cardiovascular and cognitive function in postmenopausal women have been recently discredited, controversy remains regarding its usefulness for maintaining skeletal muscle mass or strength. Therefore, the purpose of this study was to determine whether estrogen use is associated with enhanced muscle composition and, if so, whether this translates into improved strength and physical function.

METHODS

Cross-sectional analysis of 840 well-functioning community-dwelling white women (current estrogen replacement therapy (ERT) users = 259, nonusers = 581) aged 70-79 yr participating in the Health, Aging and Body Composition Study. Muscle composition of the midthigh by computed tomography included cross-sectional area (CSA) of the quadriceps, hamstrings, intermuscular fat and subcutaneous fat, and muscle attenuation in Hounsfield units (HU) as a measure of muscle density. Isometric hand grip and isokinetic knee extensor strength were assessed by dynamometry. Physical function was assessed using a summary scale that included usual 6-m walk and narrow walk speed, repeated chair stands, and standing balance.

RESULTS

In analyses of covariance adjusted for relevant confounders, quadriceps muscle CSA and HU were greater in current ERT than non-ERT women (P < 0.05). Grip strength was also greater (P < 0.05) in women taking ERT while knee extensor strength approached significance (P < 0.10). However, differences in muscle composition and strength were modest at < or =3.3%. There was no difference by ERT status for the hamstring muscles, fat CSA, or for physical function.

CONCLUSION

The associations between ERT and muscle composition and strength were minor and did not translate into improved physical function. Initiation of ERT for preservation of muscle composition and function may not be indicated.

The validity of summing lower extremity individual joint kinetic measures

In the analysis of human movement, researchers often sum individual joint kinetics to obtain a single measure of lower extremity function. The extent to which these summed measures relate to the mechanical objectives of the task has not been formally validated. The criterion validity of these measures was established with comparisons to the mechanical objective of two multiple-joint tasks. For the Work task 18 participants performed a loaded barbell squat using 4 resistances while instrumented for biomechanical analysis. For the Power they performed 2 predetermined amounts of work at both self-selected and fast speeds. Using inverse dynamics techniques, the peak net joint moment (PM) was calculated bilaterally in the sagittal plane at the ankle, knee, and hip and was summed into a single measure. This measure was correlated with the task objectives using simple linear regression. Similar procedures were used for the average net joint moment (AM), peak (PP), and average (AP) net joint moment power, and the net joint moment impulse (IM) and work (IP). For the Work task all 6 measures were significantly correlated with the task objective, but only AM, PM, and IP had correlation coefficients above 0.90. For the Power task, IM was not significantly correlated with the task objective, and only AP had a correlation coefficient above 0.90. These findings indicate that the validity of summing individual kinetic measures depends on both the measure chosen and the mechanical objective of the task.

Joint torques during sit-to-stand in healthy subjects and people with Parkinson's disease

OBJECTIVES

To compare lower limb joint torques during sit-to-stand in normal elderly subjects and people with Parkinson's disease, using a developed biomechanical model simulating all phases of sit-to-stand.Design. A cross-sectional study utilizing a Parkinsonian and a control group.

BACKGROUND

Subjects with Parkinson's disease were observed to experience difficulty in performing sit-to-stand. The developed model was used to calculate the lower limb joint torques in normal elderly subjects and subjects with Parkinson's disease, to delineate possible causes underlying difficulties in initiating sit-to-stand task.

METHODS

Six normal elderly subjects and seven age-matched subjects with Parkinson's disease performed five sit-to-stand trials at their self-selected speed. Anthropometric data, two-dimensional kinematic and foot-ground and thigh-chair reactive forces were used to calculate, via inverse dynamics, the joint torques during sit-to-stand in both before and after seat-off phases. The difference between the control and Parkinson's disease group was analysed using independent t-tests.

RESULTS

Both control and Parkinson's disease groups had a similar joint kinematic pattern, although the Parkinson's disease group demonstrated a slower angular displacement. The latter subjects produced significantly smaller normalized hip flexion torque and presented a slower torque build-up rate than the able-bodied subjects (P<0.05).

CONCLUSION

Slowness of sit-to-stand in people with Parkinson's disease could be due to a reduced hip flexion joint torque and a prolonged rate of torque production.

The relationship between leg power and physical performance in mobility-limited older people

OBJECTIVES

The purpose of this study was to assess the influence of leg power and leg strength on the physical performance of community-dwelling mobility-limited older people.

DESIGN

Cross-sectional analysis of baseline data from a 12-week randomized controlled exercise-intervention study.

SETTING

Exercise laboratory within the Department of Health Science of an urban university.

PARTICIPANTS

Forty-five community-dwelling mobility-limited people (34 women, 11 men), aged 65 to 83.

MEASUREMENTS

Health status, depression, cognition, physical activity, and falls efficacy; physiological measures of lower extremity strength and power; and measures of physical performance.

RESULTS

Through bivariate analyses, leg power was significantly associated with physical performance as measured by stair-climb time, chair-stand time, tandem gait, habitual gait, maximal gait, and the short physical performance battery describing between 12% and 45% of the variance (R2). Although leg power and leg strength were greatly correlated (r = .89) in a comparison of bivariate analyses of strength or power with physical performance, leg power modeled up to 8% more of the variance for five of six physical performance measures. Despite limitations in sample size, it appeared that, through quadratic modeling,the influence of leg power on physical performance was curvilinear. Using separate multivariate analyses, partial R2 values for leg power and leg strength were compared, demonstrating that leg power accounted for 2% to 8% more of the variance with all measures of physical performance.

CONCLUSION

Leg power is an important factor influencing the physical performance of mobility-limited older people. Although related to strength, it is a separate attribute that may exert a greater influence on physical performance. These findings have important implications for clinicians practicing geriatric rehabilitation.

Relationship between knee extension force and stand-up performance in community-dwelling elderly women

OBJECTIVE

To describe the relationship between knee extension force and stand-up performance.

DESIGN

Prospective, cross-sectional, descriptive, and correlational.

SETTING

Community.

PARTICIPANTS

Fifty-five community-dwelling women 60 or more years old.

INTERVENTIONS

Information pertaining to stand-up performance was gathered via structured questions. The time to complete 1 sit-to-stand from a bench of known height (16in) was obtained in conjunction with subjects' ratings of perceived exertion (RPEs) relative to the task. Bilateral lower extremity knee extension strength was measured with a hand-held dynamometer and normalized against body weight.

MAIN OUTCOME MEASURES

Total knee extension forces (raw and body-weight normalized values) generated by each subject were correlated with 3 measures of stand-up performance.

RESULTS

Low to moderate correlations (r = -.323 to -.526) were found between knee extension forces and the stand-up performance measures of bench stand time and stand-up difficulties. Normalized knee extension force had a higher correlation than raw knee extension force with stand-up difficulties and RPE. Correlations were higher when the curvilinear nature of the relationship was taken into account. The highest correlation was between normalized knee extension force and the RPE associated with the bench stand task (r = -.767).

CONCLUSION

Knee extension force offers an important but incomplete explanation of stand-up performance from low surfaces by elderly women. Interventions leading to increased knee extension force may improve stand-up performance.

Lower-Extremity Kinetic Response to Activity Program Dosing in Older Adults

The purpose of this investigation was to determine the effects of two doses of a weighted vest on acute lower-extremity gait kinetics in older adults. Peak ankle, knee, and hip net joint moments were quantified in 56 men and women volunteers (73.8 ± 6.9 years old) enrolled in a 6-month physical activity study. At the initial study visit, participants underwent 6 walking trials (3 with vest, 3 without vest) at their normal pace. During the vest-wearing trials, participants wore a vest loaded with either 0% of body weight (BW) (n= 19), 3% of BW (n= 16), or 5% of BW (n= 21). With acute application of the vests, maximum peak plantarflexion moments increased by 5.7% in the 5% BW group compared to the 0% BW group,p< 0.01. Compared to the 0% vest-weight group, knee extension moments increased by 13.8% when 5% BW was applied,p< 0.01; a marginally significant treatment effect was evident in the 3% BW group,p= 0.04. Despite these acute alterations, knee strength and physical performance did not improve when subjects wore the vests 2 hours a day, 4 days a week for 27 weeks, without additional exercise prescription. These findings suggest that: (a) the acute changes in vest-mediated lower-extremity kinetics are not systemic but joint specific and load dependent, and (b) weighted vest prescription should be greater than 5% BW without prescribed exercise, or should include prescribed exercises, to invoke long-term strength and physical performance gains in older adults.

Knee strength and lower- and higher-intensity functional performance in older adults

PURPOSE

This study characterizes the linear relations among knee strength, work capacity, and lower- and higher-intensity measures of functional performance in ambulatory, high-functioning older adults.

METHODS

Sixty-two seniors (average age = 73.4 +/- 7.3 yr) participated in the study. Isokinetic measures included the peak flexion/extension torque produced during five continuous repetitions and the total flexion/extension work performed during 20 repetitions (60 degrees x s(-1)). Functional measures included lower-intensity tests (timed 8-foot and 50-foot walking tests at the participants' "normal" pace, and a standing reach task) and higher-intensity tests (a timed 50-foot "brisk" walk, timed chair stands, and a timed stair climb).

RESULTS

Isokinetic strength and work capacity measures explained between 41% and 54% of the variance in the higher-intensity functional models and only between 31% and 33% of the variance in the lower-intensity models. The strength of the associations, approximated by the beta coefficients of the strength and work terms, was also greater for the higher-intensity functional tasks.

CONCLUSIONS

Further research is warranted to determine whether exercises that increase knee strength and work capacity, improve brisk walking, stair climbing, and chair standing capabilities in older adults.

Nature of age-related changes in muscle strength of the extremities of women

Age-related changes in the muscle strength of the extremities of 123 women (20-79 years) were measured using a hand-held dynamometer. The isometric strength of three upper- and three lower-extremity muscle actions declined across ages. The magnitudes of strength decreases were a function of both the action and side tested. The earlier and steeper strength declines in actions of functional importance, e.g., knee extension, should alert those working with aging women of the potential importance of strengthening such muscle actions.

Comparative effects of high- and low-intensity resistance training on thigh muscle strength, fiber area, and tissue composition in elderly women

The effects of 52 weeks resistance training at one of two exercise intensities on thigh muscle strength, fiber cross-sectional area (CSA), and tissue composition were studied in healthy 65-79-year-old women. Subjects were assigned to either a control (CO), high-intensity (HI) or low-intensity (LO) training group. Exercise regimens consisted of three sets of leg press, knee extension, and knee flexion exercises, 3 days/week, at either 80% of one-repetition maximum (1-RM) for seven repetitions (HI) or 40% of 1-RM for 14 repetitions (LO). Dynamic muscle strength was evaluated by 1-RM, thigh lean tissue mass (LTM), fat mass, and bone mineral density (BMD, g/cm2) by dual energy X-ray absorptiometry, and fiber CSA of vastus lateralis m. by histomorphometry. Muscle strength increased, on average (+/- SEM), by 59.4 +/- 7.9% and 41.5 +/- 7.9% for HI and LO, respectively, compared to 1.3 +/- 4.8% in CO (P = 0.0001). Type I fiber CSA increased over time (P < 0.05) in both exercise groups, with a trend for increased type II area (HI, P = 0.06; LO, P = 0.11). There was no significant effect of either exercise program on thigh tissue composition, except for BMD at the 1/3 site (middle third of the femur), where LO and CO groups experienced a decline (P < 0.05) of -2.2 +/- 0.5% and -1.8 +/- 0.6%, respectively, while HI maintained BMD (+1.0 +/- 1.0%). Both training programs produced significant gains in thigh muscle strength, which were associated with fiber hypertrophy, although these did not translate into appreciable alterations in thigh tissue composition.