Knee Extension Isokinetic Strength Research Articles

Foreign allometric exponents adequately normalize isokinetic knee extension strength to identify muscle weakness and mobility limitation in Portuguese older adults: a cross-sectional study

BackgroundIdentifying muscle weakness is challenging, because the reduction of strength with aging does not depend only on sarcopenia, but also on sensorimotor deficits. Nevertheless, this identification is improved by adjusting muscle strength allometrically, by removing the influence of body size. However, the effectiveness of foreign models to normalize these (dys)functionalities is not yet tested. This study aimed to compare and apply foreign allometric exponents for normalizing isokinetic knee extension strength in Portuguese older adults to identify muscle weakness/mobility limitation. Additionally, to attest any populational difference, data of these people and Brazilian older adults were comparedMethodsThis is a cross-sectional study encompassing 226 Portuguese (n = 132) and Brazilian (n = 94) older adults. Mobility limitation (six-minute walk test, at lowest quartile), lower limb strength (knee extension isokinetic strength at 60º/s), and body dimensions measures were taken. Foreign allometric exponents (b) were used to normalize Portuguese strength (strength/body-size variablesb). Non-normalized and normalized strength were compared (ROC) to generate the most accurate cut-point for identifying muscle weakness/mobility limitation.ResultsOlder Portuguese men and women had better mobility than their Brazilian counterparts. Older Portuguese women had superior muscle strength to Brazilian women. Normalization from 11 foreign models removed the influence of body size on muscle strength, with a negligible correlation (r ≤ 0.30). In contrast to the non-normalized strength, the normalized strength cut-off points were sufficiently accurate (AUC ≥ 0.70) to avoid identifying false-negative cases of weakness/mobility limitation.ConclusionsPortuguese older women were stronger and had superior functional capacity compared to Brazilian ones. Normalized foreign models improved the accuracy in identifying muscle weakness/mobility limitation in Portuguese older adults. The isokinetic knee extension muscle strength normalized, even using foreign allometric exponents, should be better than no adjustment.

Asymmetry Of Knee Extension Strength And Single-leg Landing Impact In ACL reconstructed Athletes

PURPOSE: Excessive magnitude, speed, and asymmetry of single-leg landing impacts contribute to re-injury risk in athletes after ACL reconstruction (ACLR). The limb symmetry index (LSI) of knee strength tends to decrease after ACLR even after return to sport. We analyzed relationships between the asymmetry of vertical ground reaction force (VGRF) parameters during single-leg jump landings and the knee isokinetic extension strength in athletes after ACLR. METHODS: Twenty-six participants were recruited based on the inclusion criteria: age 16-40 years at time of measurement; primary or one-sided ACL injury; >150 and <240 days since anatomical double-bundle ACLR using a hamstring tendon autograft; completed athletic rehabilitation within the same protocol; and agreement to participate in single-leg hop exercise and basic noncontact practice of jump-landings and cutting sports. The isokinetic strength of the quadriceps was tested at an angle of 60°/sec. Participants were subdivided into groups according to LSI for quadriceps strength (low quadriceps [LQ], <85% LSI, N10; high quadriceps [HQ], >90% LSI, N12). A 20-cm step was placed 60 cm from the center of a force plate. The participants stood on one leg on the step with their arms crossed, then jumped forward without any intended upward action and landed as naturally as possible on the same leg in the center of the force plate. The VGRF was collected at a sampling rate of 1000 Hz, filtered using a low-pass Butterworth filter with a cut-off frequency of 50 Hz, and normalized by body weight. Loading rate was calculated as peak VGRF (pVGRF) divided by the time from initial contact to pVGRF. The LSI of pVGRF and loading rate were compared between groups using non-paired t-tests. RESULTS: The quadriceps strength LSI of the LQ and HQ groups were 76±6.7% and 96.5±7.2%, respectively. The pVGRF LSI were 104.0±1.3% and 98.0±8.7%, respectively. Loading rate LSI were 115.9±23.6% and 98.8±21.7%, respectively. Loading rate LSI of LQ was significant larger than HQ (p=0.041). The pVGRF LSI of LQ tended to be larger than HQ (p=0.074). CONCLUSIONS: Smaller asymmetry in knee extension isokinetic strength is important for symmetrical landing impact during single-leg anterior jump-landings performed by athletes after ACLR. Supported by JSPS KAKENHI Grant number 26350606.

Early body composition, but not body mass, is associated with future accelerated decline in muscle quality.

BackgroundMuscle quality (MQ) or strength‐to‐mass ratio declines with aging, but the rate of MQ change with aging is highly heterogeneous across individuals. The identification of risk factors for accelerated MQ decline may offer clues to identity the underpinning physiological mechanisms and indicate targets for prevention and treatment. Using data from the Baltimore Longitudinal Study of Aging, we tested whether measures of body mass and body composition are associated with differential rates of changes in MQ with aging.MethodsParticipants included 511 men and women, aged 50 years or older, followed for an average of 4 years (range: 1–8). MQ was operationalized as ratio between knee‐extension isokinetic strength and CT‐thigh muscle cross‐sectional area. Predictors included body mass and body composition measures: weight (kg), body mass index (BMI, kg/m2), dual‐energy x‐ray absorptiometry‐measured total body fat mass (TFM, kg) and lean mass (TLM, kg), and body fatness (TFM/weight). Covariates were baseline age, sex, race, and body height.ResultsMuscle quality showed a significant linear decline over the time of the follow up (average rate of decline 0.02 Nm/cm2 per year, P < .001). Independent of covariates, neither baseline body weight (P = .756) nor BMI (P = .777) was predictive of longitudinal rate of decline in MQ. Instead, higher TFM and lower TLM at baseline predicted steeper longitudinal decline in MQ (P = .036 and P < .001, respectively). In particular, participants with both high TFM and low TLM at baseline experienced the most dramatic decline compared with those with low TFM and high TLM (about 3% per year vs. 0.5% per year, respectively). Participants in the higher tertile of baseline body fatness presented a significantly faster decline of MQ than the rest of the population (P = .021). Similar results were observed when body mass, TFM, and TLM were modeled as time‐dependent predictors.ConclusionsBody composition, but not weight nor BMI, is associated with future MQ decline, suggesting that preventive strategies aimed at maintaining good MQ with aging should specifically target body composition features.

Muscle strength mediates the relationship between mitochondrial energetics and walking performance.

SummarySkeletal muscle mitochondrial oxidative capacity declines with age and negatively affects walking performance, but the mechanism for this association is not fully clear. We tested the hypothesis that impaired oxidative capacity affects muscle performance and, through this mechanism, has a negative effect on walking speed. Muscle mitochondrial oxidative capacity was measured by in vivo phosphorus magnetic resonance spectroscopy as the postexercise phosphocreatine resynthesis rate, kPC r, in 326 participants (154 men), aged 24–97 years (mean 71), in the Baltimore Longitudinal Study of Aging. Muscle strength and quality were determined by knee extension isokinetic strength, and the ratio of knee extension strength to thigh muscle cross‐sectional area derived from computed topography, respectively. Four walking tasks were evaluated: a usual pace over 6 m and for 150 s, and a rapid pace over 6 m and 400 m. In multivariate linear regression analyses, kPC r was associated with muscle strength (β = 0.140, P = 0.007) and muscle quality (β = 0.127, P = 0.022), independent of age, sex, height, and weight; muscle strength was also a significant independent correlate of walking speed (P < 0.02 for all tasks) and in a formal mediation analysis significantly attenuated the association between kPC r and three of four walking tasks (18–29% reduction in β for kPC r). This is the first demonstration in human adults that mitochondrial function affects muscle strength and that inefficiency in muscle bioenergetics partially accounts for differences in mobility through this mechanism.