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Background: Hip fracture may result in an asymmetrical lower-limb strength deficit. The deficit may be related to the trauma, surgical treatment, pain, or disuse of the fractured limb. However, disease and injury burden or musculoskeletal pain in the other limb may reduce muscle strength on that side, reducing the asymmetrical deficit. The aim of our study was to explore the asymmetrical strength deficit and to determine the potential underlying factors in patients from six months to seven years after a hip fracture.Methods: The asymmetrical deficit was calculated ([fractured limb/sum of both lower limbs] x 100%) for isometric knee extension torque, rate of force development during isometric testing, and leg extension power. The asymmetrical measures for lower-limb muscle mass (fractured limb--nonfractured limb), and that of lower-limb pain and disease and injury burden (nonfractured limb--fractured limb), were calculated.Results: Half of the participants had no consistent asymmetrical deficit on the fractured side. Regression analyses showed that asymmetrical measures of lower-limb pain, muscle mass, and disease and injury burden predicted asymmetrical deficit in knee extension torque (R(2) = 0.43) and in the rate of force development (R(2) = 0.36). More intense pain and disease and injury burden affecting the nonfractured limb and smaller muscle mass relative to the fractured limb were associated with a smaller asymmetrical deficit.Conclusions: Following a hip fracture, the prevention of decreases in muscle strength and power as well as a large asymmetrical deficit by the use of targeted pain management and rehabilitation may help to reduce the risk of subsequent mobility limitations and falls. [ABSTRACT FROM AUTHOR]

OBJECTIVE: After hip fracture, muscle strength and power remain persistently poor, especially in the fractured leg. This study explores whether asymmetrical leg extension power (LEP) deficit affects mobility in women after proximal femoral fracture (PFF). DESIGN: In this observational study, LEP of both legs, 10- and 50-foot walking speed, and stair-climbing speed were measured in 43 women, aged 73-96, at 1 and 13 wks after surgical repair of PFF. Asymmetrical LEP deficit was calculated as (fractured/(sum both legs)) x 100%. RESULTS: Between weeks 1 and 13 after PFF surgery, LEP increased in the fractured and nonfractured legs by 100% and 30%, respectively. Asymmetrical deficit was reduced from 28.5 +/- 10.2% to 40.4 +/- 8.6%. Linear regression analyses showed that poorer LEP of the nonfractured leg at week 1 correlated significantly with slower walking (beta > 0.525, P < 0.001) and stair-climbing speed (beta > 0.349, P < 0.016) and predicted poorer mobility 12 wks later (beta > 0.354, P < 0.020). Large asymmetrical LEP deficit was cross-sectionally associated with slow stair-climbing speed (beta > 0.343, P < 0.018) at weeks 1 and 13, but not with walking speed. CONCLUSIONS: Higher LEP of the nonfractured leg predicted better recovery of mobility after PFF. Larger asymmetrical LEP deficit correlated with limitation in climbing stairs-a more challenging mobility task where fluent performance requires unilateral force production. [ABSTRACT FROM AUTHOR]

PURPOSE: This study examined the relative contribution of genetic and environmental effects on maximal leg extensor power and also investigated whether leg extensor power and maximum voluntary isometric knee extensor strength share a genetic component. METHODS: Muscle functions were measured as part of the Finnish Twin Study on Aging in 101 monozygotic (MZ) and 116 dizygotic (DZ) female twin pairs aged 63-76 yr. Leg extensor power was measured using the Nottingham Leg Extensor Power Rig and maximum voluntary isometric knee extensor strength using an adjustable dynamometer chair. The analyses were carried out using the maximum likelihood method in Mx-program on the raw data set. RESULTS: A bivariate Cholesky decomposition model showed that leg extensor power and isometric knee extensor strength shared a genetic component in common, which accounted for 32% of the total variance in leg extensor power and 48% in isometric knee extensor strength. In addition, power and strength had a nonshared environmental effect in common accounting for four percent of the variance in power and 52% in strength. Remaining variance for leg extensor power was due to trait-specific shared and nonshared environmental effects. CONCLUSION: Observed genetic effect in common for leg extensor power and maximum voluntary isometric knee extensor strength indicated that these two traits are regulated by the same genes. However, also environmental effects have a significant role in explaining the variability in power and strength. [ABSTRACT FROM AUTHOR]

Purpose: Older adults walk slower than young adults, but it is not known why. Previous research suggests that ankle plantarflexors may have a crucial role in the reduction of walking speed. The purpose of this study was to investigate age-related differences in triceps surae muscle-tendon function during walking to further investigate the role of plantarflexors in the age-related reduction of walking speed., Methods: Medial gastrocnemius and soleus muscle fascicle lengths were measured using ultrasound imaging during walking from 13 young (25 ± 4 yr) men at preferred walking speed and from 13 older (73 ± 5 yr) men at preferred speed and at the young men's preferred speed. Muscle-tendon unit lengths were calculated from joint kinematics, and tendinous tissue lengths were calculated by subtracting muscle lengths from muscle-tendon unit lengths. In addition, ground reaction forces and electromyographic activity of medial gastrocnemius and soleus were measured., Results: In both medial gastrocnemius and soleus, it was observed that at preferred walking speed, older men used a narrower muscle fascicle operating range and lower shortening velocity at the estimated time of triceps surae peak force generation compared with young men. Fascicles also accounted for a lower proportion of muscle-tendon unit length changes during the stance phase in older compared with young men. Significant differences in triceps surae muscle function were not observed between age groups when compared at matched walking speed., Conclusions: In older men, walking at preferred speed allows triceps surae muscles to generate force with more favorable shortening velocity and to enhance use of tendinous tissue elasticity compared with walking at young men's preferred speed. The results suggest that older men may prefer slower walking speeds to compensate for decreased plantarflexor strength.

Purpose: While the lack of muscular activity is a proposed trigger for metabolic alterations, this association has not been directly measured. We examined the associations between EMG-derived muscle inactivity and activity patterns and cardiometabolic biomarkers in healthy, physically active adults., Methods: Data for this cross-sectional study were pooled from two studies (EMG24 and InPact), resulting in a sample of 150 individuals without known chronic diseases and with high-quality EMG data (female n = 85, male n = 65, age = 38.8 ± 10.6 yr, body mass index = 23.8 ± 3.1 kg·m⁻²). EMG was measured during one to three typical weekdays using EMG shorts, measuring quadriceps and hamstring muscle EMG. Muscle inactivity time and moderate- to vigorous-intensity muscle activity were defined as EMG amplitude below that of standing still and above that of walking 5 km·h⁻¹, respectively. Blood pressure index, waist circumference, fasting plasma glucose, HDL cholesterol, and triglycerides were measured, and long-term exercise behaviors were assessed by questionnaire., Results: In a group of physically active participants, muscles were inactive for 65.2% ± 12.9% of the measurement time in an average of 24.1 ± 9.8-s periods. Compared to those in the lowest muscle inactivity quartile (<55.5% of measurement time), those in the highest quartile (≥74.8% of measurement time) had 0.32 mmol·L⁻¹ lower HDL cholesterol (P < 0.05) and 0.30 mM higher triglycerides (P < 0.05) independent of muscle's moderate- to vigorous-intensity activity., Conclusions: Clinically significant differences in HDL cholesterol and triglycerides were found, favoring participants having low muscle inactivity time, independent of moderate- to vigorous-intensity muscle activity. Even physically active individuals may benefit from light-intensity activities that reduce ubiquitous muscle inactivity time.

Purpose: Interventions targeting sedentary time are needed. We used detailed EMG recordings to study the short-term effectiveness of simple sedentary time-targeted tailored counseling on the total physical activity spectrum., Methods: This cluster randomized controlled trial was conducted between 2011 and 2013 (InPact, ISRCTN28668090), and short-term effectiveness of counseling is reported in the present study. A total of 133 office workers volunteered to participate, from which muscle activity data were analyzed from 48 (intervention, n = 24; control, n = 24). After a lecture, face-to-face tailored counseling was used to set contractually binding goals regarding breaking up sitting periods and increasing family based physical activity. Primary outcome measures were assessed 11.8 ± 1.1 h before and a maximum of 2 wk after counseling including quadriceps and hamstring muscle inactivity time, sum of the five longest muscle inactivity periods, and light muscle activity time during work, commute, and leisure time., Results: Compared with those in the controls, counseling decreased the intervention group's muscle inactivity time by 32.6 ± 71.8 min from 69.1% ± 8.5% to 64.6% ± 10.9% (whole day, P < 0.05; work, P < 0.05; leisure, P < 0.05) and the sum of the five longest inactivity periods from 35.6 ± 14.8 to 29.7 ± 10.1 min (whole day, P < 0.05; leisure, P < 0.01). Concomitantly, light muscle activity time increased by 20.6 ± 52.6 min, from 22.2% ± 7.9% to 25.0% ± 9.7% (whole day, P < 0.05; work, P < 0.01; leisure, P < 0.05), and during work time, average EMG amplitude (percentage of EMG during maximal voluntary isometric contraction (MVC) (%EMG MVC)) increased from 1.6% ± 0.9% to 1.8% ± 1.0% (P < 0.05) in the intervention group compared with that in the controls., Conclusions: A simple tailored counseling was able to reduce muscle inactivity time by 33 min, which was reallocated to 21 min of light muscle activity. During work time, average EMG amplitude increased by 13%, reaching an average of 1.8% of EMG MVC. If maintained, this observed short-term effect may have health-benefiting consequences.

Background: Long-term physical inactivity seems to cause many health problems. We studied whether persistent physical activity compared with inactivity has a global effect on serum metabolome toward reduced cardiometabolic disease risk., Methods and Results: Sixteen same-sex twin pairs (mean age, 60 years) were selected from a cohort of twin pairs on the basis of their >30-year discordance for physical activity. Persistently (≥5 years) active and inactive groups in 3 population-based cohorts (mean ages, 31-52 years) were also studied (1037 age- and sex-matched pairs). Serum metabolome was quantified by nuclear magnetic resonance spectroscopy. We used permutation analysis to estimate the significance of the multivariate effect combined across all metabolic measures; univariate effects were estimated by paired testing in twins and in matched pairs in the cohorts, and by meta-analysis over all substudies. Persistent physical activity was associated with the multivariate metabolic profile in the twins (P=0.003), and a similar pattern was observed in all 3 population cohorts with differing mean ages. Isoleucine, α1-acid glycoprotein, and glucose were lower in the physically active than in the inactive individuals (P<0.001 in meta-analysis); serum fatty acid composition was shifted toward a less saturated profile; and lipoprotein subclasses were shifted toward lower very-low-density lipoprotein (P<0.001) and higher large and very large high-density lipoprotein (P<0.001) particle concentrations. The findings persisted after adjustment for body mass index., Conclusions: The numerous differences found between persistently physically active and inactive individuals in the circulating metabolome together indicate better metabolic health in the physically active than in inactive individuals.

Purpose: Aging diminishes the ability to run fast, but the specific mechanisms responsible for this deterioration remain largely unknown. In the present study, we investigated the age-related decline in sprint running ability through a cross-sectional examination of biomechanical and skeletal muscle characteristics in 77 competitive male sprinters aged 17-82 yr., Methods: Ground reaction force (GRF) and kinematic stride cycle parameters were measured during the maximum-velocity phase using a 9.4-m-long force platform. Knee extensor (KE) and ankle plantar flexor (PF) structural characteristics were investigated using ultrasonography and muscle biopsies (vastus lateralis). Force production characteristics of leg extensor muscles were determined by dynamic and isometric contractions., Results: The main findings were as follows: 1) the progressive age-related decline in maximum running velocity (Vmax) was mainly related to a reduction in stride length (Lstr) and an increase in ground contact time (tc), whereas stride frequency showed a minor decline and swing time remained unaffected; 2) the magnitude of average braking and push-off resultant GRFs declined with age and associated with Lstr, tc, and Vmax; 3) there was an age-related decline in muscle thickness, Type II fiber area and maximal and rapid force-generating capacity of the lower limb muscles; and 4) muscle thickness (KE + PF) was a significant predictor of braking GRF, whereas the countermovement jump height explained most of the variance in push-off GRF in stepwise regression analysis., Conclusions: Age-related slowing of maximum running speed was characterized by a decline in stride length and an increase in contact time along with a lower magnitude of GRFs. The sprint-trained athletes demonstrated an age-related selective muscular atrophy and reduced force capacity that contributed to the deterioration in sprint running ability with age.