Free-Living Sit-to-Stand Characteristics as Predictors of Lower Extremity Functional Decline among Older Adults.

PURPOSE: Habitual strength and power-demanding activities of daily life may support the maintenance of adequate lower extremity functioning with aging, but this has been sparingly explored. Hence, we examined whether the characteristics of free-living sit-to-stand (STS) transitions predict a decline in lower extremity functioning over a 4-yr follow-up. METHODS: A total of 340 community-dwelling older adults (60% women; age 75, 80, or 85 yr) participated in this prospective cohort study. At baseline, a thigh-worn accelerometer was used continuously (3-7 d) to monitor the number and intensity of free-living STS transitions. A decline in lower extremity functioning was defined as a drop of ≥2 points in the Short Physical Performance Battery (SPPB) from baseline to follow-up. Maximal isometric knee extension strength was measured in the laboratory. RESULTS: Eighty-five participants (75% women) declined in SPPB over 4 yr. After adjusting for age, sex, and baseline SPPB points, higher free-living peak STS angular velocity (odds ratio (OR), 0.70; 95% confidence interval (CI), 0.52-0.92, per 20°·s -1 increase) protected against a future decline. When adjusting the model for maximal isometric knee extension strength, the statistical significance was attenuated (OR = 0.72; 95% CI = 0.54-0.96, per 20°·s -1 increase). CONCLUSIONS: Performing STS transitions at higher velocities in the free-living environment can prevent a future decline in lower extremity function. This indicates that changes in daily STS behavior may be useful in the early identification of functional loss. Free-living peak STS angular velocity may be a factor underlying the longitudinal association of lower extremity strength and performance.

Minimal power required to ascend a flight of stairs versus actual power measured with body-fixed sensors in adults aged 19-85 years.

A good stair-climbing (SC) ability is crucial for independent living in older adults. A simple formula that estimates the mean power needed to ascend a flight of stairs in a predetermined time (i.e., total ascent duration) is easy to implement in practice, but lacks information on actual power values generated per step. The latter is possible with body-fixed sensors. This study aimed at comparing both methodologies and investigating their sensitivity to detect age-related differences. 318 participants (162 ♀; age 19-85 years) were tested on a 6-step staircase and two methodologies were used to estimate mean SC power: (1) a body-fixed sensor with automated detection of power production per step, and (2) a mathematic equation based on timed ascent duration, body mass and stair height. SC power was 210.4 W lower with formula compared to sensor, lower in women versus men and in older versus young adults (p < 0.001). The difference in SC power between sensor and formula was greater in individuals with better performance (i.e., men and young adults) (p < 0.001), indicating a ceiling effect of the formula in well-functioning and younger individuals. Likewise, ICC's between both methodologies showed poor reliability in people aged <65 years (0.087-0.363) and moderate to good reliability in people aged ≥65 years (0.453-0.780). To conclude, participants with better SC performance are able to largely overshoot the minimal power required to ascend the stairs in a certain duration. This makes the sensor more sensitive to identify early age-related differences compared to the formula.

Older adults' lower-limb muscle power production throughout a full flight of stairs: Reliability and comparison between different stair models.

Lower-limb muscle power should be closely monitored to prevent age-related functional ability declines. Stair-climbing (SC) power is a functionally relevant measurement of lower-limb muscle power. Body-fixed sensors can measure power production throughout the different steps of a flight of stairs to assess different aspects of performance. This study investigated: 1) power production throughout a full flight of stairs; 2) if staircases with less or more steps can provide similar information; and 3) test-retest reliability of SC power. 116 community-dwelling older adults (57 women) ascended three staircases as fast as possible: 12, 6 and 3 steps. Mean vertical power production per step was collected and analyzed using a commercial body-fixed sensor and software. Three phases were found in SC power production: 1) an acceleration phase, i.e., the power produced in step 1 (P1); 2) a phase where the highest performance (Pmax) is reached and; 3) a fatiguing phase with power loss (Ploss; only measurable on 12-step staircase). Mean power (Pmean) over the different steps was also evaluated. P1 did not differ between staircases (all p>0.05), whereas Pmax and Pmean were higher with increasing number of steps (p = 0.073 -p<0.001). P1, Pmax and Pmean were strongly correlated between staircases (r = 0.71-0.95, p<0.05). and showed good to excellent reliability (ICC = 0.66-0.95, p<0.05). Ploss showed poor reliability. To conclude, measurements of SC power production (P1, Pmax and Pmean) with a single sensor on the lower back are reliable across different staircases. A small, transportable, 3-step staircase can be used for measuring power production in clinical practices with no access to regular staircases. However, absolute values are dependent on the number of steps, indicating that measurements to track performance changes over time should always be done using an identical stair model.

Sensor- and equation-based sit-to-stand power: The effect of age and functional limitations.

Estimating lower-limb muscle power during sit-to-stand (STS) tests is feasible for large-scale implementation. This study investigated 1) whether age, functional limitations and sex have an influence on the movement strategy and power production during STS; and 2) potential differences between STS power estimated with either a simple equation or a sensor. Five-repetition STS data of 649 subjects (♂352 ♀297) aged 19 to 93 years were included. Subjects were divided in different age groups and levels of functioning. A body-fixed sensor measured (sub)durations, trunk movement (flexion/extension) and STS muscle power (Psensor). Additionally, mean STS muscle power was calculated by a mathematic equation (Alcazar et al., 2018b)Results revealed that 1) older subjects and women showed greater trunk flexion before standing up than younger subjects and men, respectively (both p < 0.001); 2) well-functioning adults seemed to have the tendency to not extend the trunk fully during the sit-to-stand transition (mean difference extension - flexion range = -15.3° to -13.1°, p < 0.001); 3) mobility-limited older adults spent more time in the static sitting and standing positions than their well-functioning counterparts (all p < 0.001); 4) STS power decreased with age and was lower in women and in limited-functioning subjects compared to men and well-functioning subjects, respectively (p < 0.05); 5) Pformula was highly related to Psensor (ICC = 0.902, p < 0.001); and 6) Pformula demonstrated higher values than Psensor in well-functioning adults [mean difference = -0.31 W/kg and -0.22 W/kg for men and women, respectively (p < 0.001)], but not among limited-functioning older adults. To conclude, this study showed that age and functional limitations have an influence on the movement strategy during a 5-repetition STS test. Differences in movement strategy can affect the comparison between Pformula and Psensor. In well-functioning older adults, Pformula was slightly higher than Psensor, which might be related to an incomplete extension in the sit-to-stand transition.

Association of Sit-to-Stand Capacity and Free-Living Performance Using Thigh-Worn Accelerometers among 60- to 90-Yr-Old Adults.

PURPOSE: Five times sit-to-stand (STS) test is commonly used as a clinical assessment of lower-extremity functional ability, but its association with free-living performance has not been studied. Therefore, we investigated the association between laboratory-based STS capacity and free-living STS performance using accelerometry. The results were stratified according to age and functional ability groups. METHODS: This cross-sectional study included 497 participants (63% women) 60-90 yr old from three independent studies. A thigh-worn triaxial accelerometer was used to estimate angular velocity in maximal laboratory-based STS capacity and in free-living STS transitions over 3-7 d of continuous monitoring. Functional ability was assessed with short physical performance battery. RESULTS: Laboratory-based STS capacity was moderately associated with the free-living mean and maximal STS performance ( r = 0.52-0.65, P < 0.01). Angular velocity was lower in older compared with younger and in low- versus high-functioning groups, in both capacity and free-living STS variables (all P < 0.05). Overall, angular velocity was higher in capacity compared with free-living STS performance. The STS reserve (test capacity - free-living maximal performance) was larger in younger and in high-functioning groups compared with older and low-functioning groups (all P < 0.05). CONCLUSIONS: Laboratory-based STS capacity and free-living performance were found to be associated. However, capacity and performance are not interchangeable but rather provide complementary information. Older and low-functioning individuals seemed to perform free-living STS movements at a higher percentage of their maximal capacity compared with younger and high-functioning individuals. Therefore, we postulate that low capacity may limit free-living performance.

Ten-year longitudinal changes in muscle power, force, and velocity in young, middle-aged, and older adults.

BACKGROUND: Maximum muscle power (Pmax ) is a biomarker of physical performance in all ages. No longitudinal studies have assessed the effects of aging on Pmax obtained from the torque-velocity (T-V) relationship, which should be considered the 'gold standard'. This study evaluated the longitudinal changes in the T-V relationship and Pmax of the knee-extensor muscles in young, middle-aged, and older adults after 10 years of follow-up. METHODS: Four hundred eighty-nine subjects (311 men and 178 women; aged 19-68 years) were tested at baseline and after a 10-year follow-up. Anthropometric data, daily protein intake, physical activity level (PAL), and knee-extension muscle function (isometric, isokinetic, and isotonic) were evaluated. A novel hybrid equation combining a linear and a hyperbolic (Hill-type) region was used to obtain the T-V relationship and Pmax of the participants, who were grouped by sex and age (young: 20-40 years; middle-aged: 40-60 years; and old: ≥60 years). Linear mixed-effect models were used to assess effects of time, sex, and age on T-V parameters, Pmax , and body mass index (BMI). Additional analyses were performed to adjust for changes in daily protein intake and PAL. RESULTS: Pmax decreased in young men (-0.6% per year; P < 0.001), middle-aged men and women (-1.1% to -1.4% per year; P < 0.001), and older men and women (-2.2% to -2.4% per year; P ≤ 0.053). These changes were mainly related to decrements in torque at Pmax at early age and to decrements in both torque and velocity at Pmax at older age. BMI increased among young and middle-aged adults (0.2% to 0.5% per year; P < 0.001), which led to greater declines in relative Pmax in those groups. S/T0 , that is, the linear slope of the T-V relationship relative to maximal torque, exhibited a significant decline over time (-0.10%T0 ·rad·s-1 per year; P < 0.001), which was significant among middle-aged men and old men and women (all P < 0.05). Annual changes in PAL index were significantly associated to annual changes in Pmax (P = 0.017), so the overall decline in Pmax was slightly attenuated in the adjusted model (-5.26 vs. -5.05 W per year; both P < 0.001). CONCLUSIONS: Pmax decreased in young, middle-aged, and older adults after a 10-year follow-up. The early declines in Pmax seemed to coincide with declines in force, whereas the progressive decline at later age was associated with declines in both force and velocity. A progressively blunted ability to produce force, especially at moderate to high movement velocities, should be considered a specific hallmark of aging.

Association Between Free-Living Sit-to-Stand Transition Characteristics, and Lower-Extremity Performance, Fear of Falling, and Stair Negotiation Difficulties Among Community-Dwelling 75 to 85-Year-Old Adults.

BACKGROUND: Good sit-to-stand (STS) performance is an important factor in maintaining functional independence. This study investigated whether free-living STS transition volume and intensity, assessed by a thigh-worn accelerometer, is associated with characteristics related to functional independence. METHODS: Free-living thigh-worn accelerometry was recorded continuously for 3-7 days in a population-based sample of 75-, 80-, and 85-year-old community-dwelling people (479 participants; women n = 287, men n = 192). The records were used to evaluate the number and intensity (angular velocity of the STS phase) of STS transitions. Associations with short physical performance battery (SPPB), 5-times-sit-to-stand test (5×STS), isometric knee extension force, self-reported fear of falls, and self-reported difficulty in negotiating stairs were also assessed. RESULTS: The number of STS transitions, mean and maximal angular velocity were lower in older age groups (p < .05). All variables were higher in men than in women (p < .001) and were positively associated with SPPB total points, knee extension force (r ranged from 0.18 to 0.39, all p < .001) and negatively associated with 5×STS (r = -0.13 - -0.24, all p < .05), lower extremity functional limitations (p < .01), fear of falls (p < .01), and stair negotiation difficulties (p < .01). CONCLUSIONS: Free-living STS characteristics were related to lower-extremity performance, lower extremity functional limitations, self-reported fear of falls, and stair negotiation difficulties, which can be a sensitive indicator of impending functional decline. Moreover, STS transitions may provide an indicator of adequacy of lower-limb muscle strength among older individuals.

Updating 'Perceptions and opinions on the COVID-19 pandemic in Flanders, Belgium' with data of two additional waves of a longitudinal study.

Adding to longitudinal data of three waves that were presented in an original dataset on perceptions and behaviours regarding government measures, fear of getting ill, and media use during the COVID-19 pandemic in Flanders (Belgium), this article presents information on two additional waves that were collected at two key moments in the pandemic in the same region: in late August 2020 (W4; as infection rates increased again; N = 505) and in the middle of March 2021, exactly one year after the first data collection (W5; N = 408). In W4 and W5, new respondents were added to the longitudinal sample to strengthen cross-sectional analyses. Additional information on informal care and physical activity was also collected. These data may be of interest to researchers who wish to explore dynamics of fear and attitudes towards public health measures during this particularly challenging time.

Day-to-Day Variability and Year-to-Year Reproducibility of Accelerometer-Measured Free-Living Sit-to-Stand Transitions Volume and Intensity among Community-Dwelling Older Adults.

(1) Background: The purpose of this study was to evaluate the day-to-day variability and year-to-year reproducibility of an accelerometer-based algorithm for sit-to-stand (STS) transitions in a free-living environment among community-dwelling older adults. (2) Methods: Free-living thigh-worn accelerometry was recorded for three to seven days in 86 (women n = 55) community-dwelling older adults, on two occasions separated by one year, to evaluate the long-term consistency of free-living behavior. (3) Results: Year-to-year intraclass correlation coefficients (ICC) for the number of STS transitions were 0.79 (95% confidence interval, 0.70-0.86, p < 0.001), for mean angular velocity-0.81 (95% ci, 0.72-0.87, p < 0.001), and maximal angular velocity-0.73 (95% ci, 0.61-0.82, p < 0.001), respectively. Day-to-day ICCs were 0.63-0.72 for number of STS transitions (95% ci, 0.49-0.81, p < 0.001) and for mean angular velocity-0.75-0.80 (95% ci, 0.64-0.87, p < 0.001). Minimum detectable change (MDC) was 20.1 transitions/day for volume, 9.7°/s for mean intensity, and 31.7°/s for maximal intensity. (4) Conclusions: The volume and intensity of STS transitions monitored by a thigh-worn accelerometer and a sit-to-stand transitions algorithm are reproducible from day to day and year to year. The accelerometer can be used to reliably study STS transitions in free-living environments, which could add value to identifying individuals at increased risk for functional disability.

Relative sit-to-stand power: aging trajectories, functionally relevant cut-off points, and normative data in a large European cohort.

BACKGROUND: A validated, standardized, and feasible test to assess muscle power in older adults has recently been reported: the sit-to-stand (STS) muscle power test. This investigation aimed to assess the relationship between relative STS power and age and to provide normative data, cut-off points, and minimal clinically important differences (MCID) for STS power measures in older women and men. METHODS: A total of 9320 older adults (6161 women and 3159 men) aged 60-103 years and 586 young and middle-aged adults (318 women and 268 men) aged 20-60 years were included in this cross-sectional study. Relative (normalized to body mass), allometric (normalized to height squared), and specific (normalized to legs muscle mass) muscle power values were assessed by the 30 s STS power test. Body composition was evaluated by dual energy X-ray absorptiometry and bioelectrical impedance analysis, and legs skeletal muscle index (SMI; normalized to height squared) was calculated. Habitual and maximal gait speed, timed up-and-go test, and 6 min walking distance were collected as physical performance measures, and participants were classified into two groups: well-functioning and mobility-limited older adults. RESULTS: Relative STS power was found to decrease between 30-50 years (-0.05 W·kg-1 ·year-1 ; P > 0.05), 50-80 years (-0.10 to -0.13 W·kg-1 ·year-1 ; P < 0.001), and above 80 years (-0.07 to -0.08 W·kg-1 ·year-1 ; P < 0.001). A total of 1129 older women (18%) and 510 older men (16%) presented mobility limitations. Mobility-limited older adults were older and exhibited lower relative, allometric, and specific power; higher body mass index (BMI) and legs SMI (both only in women); and lower legs SMI (only in men) than their well-functioning counterparts (all P < 0.05). Normative data and cut-off points for relative, allometric, and specific STS power and for BMI and legs SMI were reported. Low relative STS power occurred below 2.1 W·kg-1 in women (area under the curve, AUC, [95% confidence interval, CI] = 0.85 [0.84-0.87]) and below 2.6 W·kg-1 in men (AUC [95% CI] = 0.89 [0.87-0.91]). The age-adjusted odds ratios [95% CI] for mobility limitations in older women and men with low relative STS power were 10.6 [9.0-12.6] and 14.1 [10.9-18.2], respectively. MCID values for relative STS power were 0.33 W·kg-1 in women and 0.42 W·kg-1 in men. CONCLUSIONS: Relative STS power decreased significantly after the age of 50 years and was negatively and strongly associated with mobility limitations. Our study provides normative data, functionally relevant cut-off points, and MCID values for STS power for their use in daily clinical practice.

Threshold of Relative Muscle Power Required to Rise from a Chair and Mobility Limitations and Disability in Older Adults.

PURPOSE: Being able to rise from a chair is paramount for independent living and is strongly influenced by the ability of the lower limbs to exert mechanical power. This study assessed minimal thresholds of lower-limb relative muscle power required to perform the sit-to-stand (STS) task in older adults and its association with mobility limitations and disability. METHODS: A total of 11,583 older adults (age, 60-103 yr) participated in this investigation. The 5-rep and 30-s versions of the STS test were used to assess chair rising ability. Relative power was calculated by the STS muscle power test. The minimum thresholds of power required to perform the STS tests were derived from the minimum values (i.e., "floor" effect) reported in the power tests through regression analyses. Mobility limitations and disability in activities of daily living (ADL) were recorded. RESULTS: For the average older man and woman, the thresholds to complete five STS repetitions were 1.1 and 1.0 W·kg-1, respectively, whereas the thresholds to complete one STS repetition were 0.3 W·kg-1 in both sexes. These thresholds increased linearly with height (5- and 1-rep, respectively: +0.13 and +0.03 W·kg-1 per 10-cm increase; both P < 0.001) and did not differ by sex or testing condition (both P ≥ 0.259). All participants with relative power below the 5-rep threshold presented mobility limitations, and 51%-56% of women and 36%-49% of men also showed disability in ADL (all χ2 ≥ 290.4; P < 0.001). CONCLUSION: A minimum level of relative muscle power is required to rise from a chair independently, which depends on the individual height and is associated with increased mobility limitations and disability. This information will help interpret data yielded by the STS muscle power test and may contribute to the prevention and treatment of mobility limitations in older people.

The Genetic Effect on Muscular Changes in an Older Population: A Follow-Up Study after One-Year Cessation of Structured Training.

Older adults lose muscle mass and strength at different speeds after the cessation of physical exercise, which might be genotype related. This study aimed to explore the genetic association with changes in muscle mass and strength one year after the cessation of structured training in an older population. Participants (n = 113, aged between 61 and 81 years) who performed one-year of combined fitness (n = 44) or whole-body vibration (n = 69) training were assessed one year after the cessation of the training. Whole-body skeletal muscle mass and knee strength were measured. Data-driven genetic predisposition scores (GPSs) were calculated and analysed in a general linear model with sex, age, body mass index and post-training values of skeletal muscle mass or muscle strength as covariates. Forty-six single nucleotide polymorphisms (SNPs) from an initial 170 muscle-related SNPs were identified as being significantly linked to muscular changes after cessation. Data-driven GPSs and over time muscular changes were significantly related (p < 0.01). Participants with higher GPSs had less muscular declines during the cessation period while data-driven GPSs accounted for 26-37% of the phenotypic variances. Our findings indicate that the loss of training benefits in older adults is partially genotype related.

An age-adapted plyometric exercise program improves dynamic strength, jump performance and functional capacity in older men either similarly or more than traditional resistance training.

Power declines at a greater rate during ageing and is more relevant for functional deterioration than either loss of maximum strength or muscle mass. Human movement typically consists of stretch-shortening cycle action. Therefore, plyometric exercises, using an eccentric phase quickly followed by a concentric phase to optimize power production, should resemble daily function more than traditional resistance training, which primarily builds force production capacity in general. However, it is unclear whether older adults can sustain such high-impact training. This study compared the effects of plyometric exercise (PLYO) on power, force production, jump and functional performance to traditional resistance training (RT) and walking (WALK) in older men. Importantly, feasibility was investigated. Forty men (69.5 ± 3.9 years) were randomized to 12-weeks of PLYO (N = 14), RT (N = 12) or WALK (N = 14). Leg press one-repetition maximum (1-RM), leg-extensor isometric maximum voluntary contraction (MVC) and rate of force development (RFD), jump and functional performance were evaluated pre- and post-intervention. One subject in RT (low back pain) and three in PLYO (2 muscle strains, 1 knee pain) dropped out. Adherence to (91.2 ± 4.4%) and acceptability of (≥ 7/10) PLYO was high. 1-RM improved more in RT (25.0 ± 10.0%) and PLYO (23.0 ± 13.6%) than in WALK (2.9 ± 13.7%) (p < 0.001). PLYO improved more on jump height, jump power, contraction time of jumps and stair climbing performance compared to WALK and/or RT (p < 0.05). MVC improved in RT only (p = 0.028) and RFD did not improve (p > 0.05). To conclude, PLYO is beneficial over RT for improving power, jump and stair climbing performance without compromising gains in strength. This form of training seems feasible, but contains an inherent higher risk for injuries, which should be taken into account when designing programs for older adults.

Age-related differences in vastus lateralis fascicle behavior during fast accelerative leg-extension movements.

Leg-extensor rate of power development (RPD) decreases during aging. This study aimed to identify the underlying mechanism of the age-related decline in RPD during a fast acceleration in terms of in vivo vastus lateralis (VL) fascicle shortening behavior. Thirty-nine men aged between 25 and 69 years performed three maximal isokinetic leg-extensor tests with a fixed initial acceleration of 45° knee extension in 150 ms until 340°/s knee angular velocity. RPD, VL activity, and ultrasound images were recorded to assess (relative) fascicle shortening and mean shortening velocity for the phases of electromechanical delay, pretension, and acceleration. Our findings show that fascicle shortening and mean shortening velocity during a fast action increase with aging (0.002 per year, P = .035 and 0.005 s-1 per year, P = .097, respectively), mainly due to a higher amount of shortening in the phase of electromechanical delay. The ratio of VL fascicle length over upper leg length at rest showed a negative correlation (r = -.46, P = .004) with RPD/body mass, while pennation angle at rest showed a trend toward a positive correlation (r = .28, P = .089). To conclude, our findings indicate that the ability to reach high VL fascicle shortening velocities in vivo is not reduced in older men while performing preprogrammed fast accelerations. The greater amount of fascicle shortening in old age is probably the result of age-related differences in the tendinous properties of the muscle-tendon complex, forcing the fascicles to shorten more in order to transmit the muscle force to the segment.

The effect of resistance training, detraining and retraining on muscle strength and power, myofibre size, satellite cells and myonuclei in older men.

INTRODUCTION: Ageing is associated with an attenuated hypertrophic response to resistance training and periods of training interruptions. Hence, elderly would benefit from the 'muscle memory' effects of resistance training on muscle strength and mass during detraining and retraining. As the underlying mechanisms are not yet clear, this study investigated the role of myonuclei during training, detraining and retraining by using PCM1 labelling in muscle cross-sections of six older men. METHODS: Knee extension strength and power were measured in 30 older men and 10 controls before and after 12 weeks resistance training and after detraining and retraining of similar length. In a subset, muscle biopsies from the vastus lateralis were taken for analysis of fibre size, fibre type distribution, Pax7+ satellite cell number and myonuclear domain size. RESULTS: Resistance training increased knee extension strength and power parameters (+10 to +36%, p < .001) and decreased the frequency of type IIax fibres by half (from 20 to 10%, p = .034). Detraining resulted in a modest loss of strength and power (-5 to -15%, p ≤ .004) and a trend towards a fibre-type specific decrease in type II fibre cross-sectional area (-17%, p = .087), type II satellite cell number (-30%, p = .054) and type II myonuclear number (-12%, p = .084). Less than eight weeks of retraining were needed to reach the post-training level of one-repetition maximum strength. Twelve weeks of retraining were associated with type II fibre hypertrophy (+29%, p = .050), which also promoted an increase in the number of satellite cells (+72%, p = .036) and myonuclei (+13%, p = .048) in type II fibres. Changes in the type II fibre cross-sectional area were positively correlated with changes in the myonuclear number (Pearson's r between 0.40 and 0.73), resulting in a stable myonuclear domain. CONCLUSION: Gained strength and power and fibre type changes were partially preserved following 12 weeks of detraining, allowing for a fast recovery of the 1RM performance following retraining. Myonuclear number tended to follow individual changes in type II fibre size, which is in support of the myonuclear domain theory.

Differences in Maximum Voluntary Excitation Between Isometric and Dynamic Contractions are Age-Dependent.

Obtaining true maximum voluntary excitation appears to be more difficult in older populations than in young populations. The aims of this study were (1) to determine whether differences in maximum voluntary excitation obtained from maximum voluntary isometric contraction (MVIC) and (sub-)maximum voluntary dynamic contraction [(s-)MVDC] are age dependent, and (2) to determine how normalizing electromyographic signals to corresponding maximum voluntary excitations affects variance between participants and the likelihood of normalized signals exceeding 100%. MVIC, s-MVDC, and MVDC were recorded in 10 young women, and MVIC and s-MVDC were recorded in 19 older women. A significant age × contraction mode interaction effect was found for vastus lateralis (P = .04). In young women, MVDC elicited the highest maximum voluntary excitation for vastus lateralis and rectus femoris (P < .05). In older women, no differences in maximum voluntary excitation were found (P > .05). Normalization to dynamic contractions resulted in lower between-participant variance of electromyography amplitudes, though not for all muscles, and decreased the number of normalized signals exceeding 100% in young women. These findings indicate that differences in maximum voluntary excitation across contraction modes are age dependent. Therefore, one should be cautious when comparing normalized signals between age groups; however, overall dynamic contractions may be preferable over isometric contractions for normalization purposes.

Bench stepping with incremental heights improves muscle volume, strength and functional performance in older women.

AIM: Task-specific exercises such as bench stepping can improve functional ability and reduce falling incidents in older adults. However, such exercises are often not optimized to improve muscle volume and force-velocity characteristics. This study determined the effects of a 12-week stepping program using incremental step heights (STEEP), on muscle volume, strength, power, functional ability and balance performance in older women. METHODS: Forty-five community-dwelling women (69y ±â€¯4) were randomly assigned to the STEEP group or a non-training CONTROL group. Training intensity was primarily determined by step height, while training volume remained equal. Thigh muscle volume (CT-scan), force-velocity characteristics of the knee extensors (Biodex dynamometer) and functional ability (Short Physical Performance Battery, timed stair ascent, 10-m walk test and countermovement jump height) were determined pre- and post-intervention. In addition, 3D trunk accelerations were recorded at the lower back to assess balance during the Short Physical Performance Battery balance tests. RESULTS: Two-way ANOVA showed that the STEEP program increased thigh muscle volume, knee extensor isometric peak torque, dynamic peak power, unloaded rate of velocity development and improved performance on all functional tests to a greater extent than CONTROL (p < .05), except the countermovement jump. No improvements were found for peak velocity and balance performance (p > .05). CONCLUSION: Our results indicate that bench step training with incremental step heights simultaneously improves functional ability, thigh muscle volume and force-velocity characteristics of the knee extensors in older women.

Effect of acceleration on the rate of power development and neural activity of the leg extensors across the adult life span.

PURPOSE: The rate of power development (RPD) represents the capacity to rapidly generate power during a dynamic muscle contraction. As RPD is highly susceptible to aging, its decline can have important functional consequences. However, the effect of age on RPD in response to rapid changes in movement velocity (cfr. fall incidence) is not yet clear. Therefore, the present study aimed to examine the effect of age on RPD and neural drive in response to different accelerations. METHODS: Three maximal isokinetic leg extensor tests at 540°/s with different initial acceleration phases at 3200, 5700 and 7200°/s2 were performed. RPD, which is the slope of the power-time curve during the acceleration phase, was calculated for 83 subjects aged between 20 and 69 years. Mean electromyography signal amplitude was determined for rectus femoris (RF), vastus lateralis (VL) and biceps femoris muscles. RESULTS: The average annual age-related decline rate of RPD at highest acceleration was - 2.93% and was - 1.52% and - 1.82% higher compared to lower acceleration rates (p < 0.001). This deficit can probably be explained by an age-related impairment in neural drive during the first 75 ms of the acceleration phase, as evidenced by a reduced RF and VL neuromuscular activity of - 0.30% and - 0.36% at highest versus lowest acceleration (p < 0.05). CONCLUSION: These findings highlight the inability of aged individuals to quickly respond to abrupt changes in movement velocity, which requires more focus in training and prevention programs.

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.