Voluntary Strength Research Articles

β-Adrenergic modulation of skeletal muscle contraction: key role of excitation-contraction coupling.

Our aim is to describe the acute effects of catecholamines/β-adrenergic agonists on contraction of non-fatigued skeletal muscle in animals and humans, and explain the mechanisms involved. Adrenaline/β-agonists (0.1-30μm) generally augment peak force across animal species (positive inotropic effect) and abbreviate relaxation of slow-twitch muscles (positive lusitropic effect). A peak force reduction also occurs in slow-twitch muscles in some conditions. β2 -Adrenoceptor stimulation activates distinct cyclic AMP-dependent protein kinases to phosphorylate multiple target proteins. β-Agonists modulate sarcolemmal processes (increased resting membrane potential and action potential amplitude) via enhanced Na(+) -K(+) pump and Na(+) -K(+) -2Cl(-) cotransporter function, but this does not increase force. Myofibrillar Ca(2+) sensitivity and maximum Ca(2+) -activated force are unchanged. All force potentiation involves amplified myoplasmic Ca(2+) transients consequent to increased Ca(2+) release from sarcoplasmic reticulum (SR). This unequivocally requires phosphorylation of SR Ca(2+) release channels/ryanodine receptors (RyR1) which sensitize the Ca(2+) -induced Ca(2+) release mechanism. Enhanced trans-sarcolemmal Ca(2+) influx through phosphorylated voltage-activated Ca(2+) channels contributes to force potentiation in diaphragm and amphibian muscle, but not mammalian limb muscle. Phosphorylation of phospholamban increases SR Ca(2+) pump activity in slow-twitch fibres but does not augment force; this process accelerates relaxation and may depress force. Greater Ca(2+) loading of SR may assist force potentiation in fast-twitch muscle. Some human studies show no significant force potentiation which appears to be related to the β-agonist concentration used. Indeed high-dose β-agonists (∼0.1μm) enhance SR Ca(2+) -release rates, maximum voluntary contraction strength and peak Wingate power in trained humans. The combined findings can explain how adrenaline/β-agonists influence muscle performance during exercise/stress in humans.

A comparison of volume-equated knee extensions to failure, or not to failure, upon rating of perceived exertion and strength adaptations

The present study aimed to compare the effects of repetition duration-, volume-, and load-matched resistance training to muscular failure (MMF) or not to muscular failure (NMF) on maximal voluntary isometric knee extensor strength. This design also allowed testing of the efficacy of "5×5" training. Nine recreationally active males (age, 21.4 ± 1.2 years; height, 1.79 ± 0.07 m; weight, 78.4 ± 7.1 kg) performed unilateral resistance training at 80% of maximal torque at 2×/week for 6 weeks. Using their nondominant leg, participants performed 5 sets of 5 repetitions (NMF). Using their dominant leg, participants performed 25 repetitions in as few sets as possible (MMF). All repetitions were performed at a pace of 2 s concentric, 1 s isometric pause, and 2 s eccentric with a 2-min rest interval between sets. Analyses identified significant pre- to post-intervention strength increases for both MMF and NMF, with effect sizes (ESs) of 2.01 and 1.65, respectively, with no significant differences between conditions (p > 0.05). Peak and mean ratings of perceived exertion (RPEs) were significantly higher for MMF compared with NMF conditions (p < 0.0001), and a tendency for significantly higher RPE values reported for later sets for the NMF condition. Total training time per session was significantly longer for NMF compared with MMF (p < 0.001). The present study suggests that in untrained participants, resistance training NMF produces equivocally the same strength increases as training to MMF when volume-matched. However, resistance training to MMF appears to be a more time-efficient protocol and may produce greater strength gains as indicated by a larger ES.

Isometric and isokinetic hip strength and agonist/antagonist ratios in symptomatic femoroacetabular impingement.

This study investigated isometric and isokinetic hip strength in individuals with and without symptomatic femoroacetabular impingement (FAI). The specific aims were to: (i) determine whether differences exist in isometric and isokinetic hip strength measures between groups; (ii) compare hip strength agonist/antagonist ratios between groups; and (iii) examine relationships between hip strength and self-reported measures of either hip pain or function in those with FAI. Cross-sectional. Fifteen individuals (11 males; 25±5 years) with symptomatic FAI (clinical examination and imaging (alpha angle >55° (cam FAI), and lateral centre edge angle >39° and/or positive crossover sign (combined FAI))) and 14 age- and sex-matched disease-free controls (no morphological FAI on magnetic resonance imaging) underwent strength testing. Maximal voluntary isometric contraction strength of hip muscle groups and isokinetic hip internal (IR) and external rotation (ER) strength (20°/s) were measured. Groups were compared with independent t-tests and Mann-Whitney U tests. Participants with FAI had 20% lower isometric abduction strength than controls (p=0.04). There were no significant differences in isometric strength for other muscle groups or peak isokinetic ER or IR strength. The ratio of isometric, but not isokinetic, ER/IR strength was significantly higher in the FAI group (p=0.01). There were no differences in ratios for other muscle groups. Angle of peak IR torque was the only feature correlated with symptoms. Individuals with symptomatic FAI demonstrate isometric hip abductor muscle weakness and strength imbalance in the hip rotators. Strength measurement, including agonist/antagonist ratios, may be relevant for clinical management of FAI.

Muscle weakness does not influence gait in unilateral cerebral palsy: A muscle strength and three-dimensional gait analysis study

Objective. The purpose of this cross-sectional study was to investigate muscle strength and possible influence on gait in high-functioning young individuals with unilateral cerebral palsy. Methods. Forty-four individuals with a mean age of 17.5 years (range 13.0–24.0 years) and 23 matched controls participated. Maximal voluntary isometric contraction was measured in a muscle strength chair. Maximal moments (torque) and muscle work were calculated from three-dimensional gait analysis. Results. The mean maximal voluntary isometric strength in knee extensors on the involved side was 1.56 Nm/kg, compared to 2.4 Nm/kg in the control group (p < 0.001). Plantar flexor strength was 1.29 compared to 2.30 Nm/kg (p < 0.001) and dorsiflexor strength was 0.18 compared to 0.47 Nm/kg (p < 0.001). Muscle strength did not correlate with muscle work performed during walking. The respective percentages of strength (Nm/kg) used during walking in relation to the strength chair measurements were 28% for knee extensors on the involved side, 102% for plantar flexors and 41% for dorsiflexors. The corresponding numbers in the control group were 33%, 66% and 48%. Conclusion. Muscle strength is decreased in the knee and ankle on the involved side in unilateral cerebral palsy, although this does not influence gait.

Motor cortex alteration and maximal voluntary strength in COPD: Impact of non-rapid eye movement sleep desaturation

Brain impairment is a major extrapulmonary effect of COPD and is involved in locomotor muscle weakness by reducing cortical motor output. Cerebrovascular O 2 reactivity (i.e. an increase in cerebral blood flow) protects the brain against the effects of chronic hypoxemia by preventing brain hypoxia. However, during non-rapid eye movement (NREM) sleep stages, patients are highly exposed to brain damage as this reactivity is abolished [1] . This study assessed the involvement of NREM sleep desaturation in decreasing cortical motor output and muscle strength in COPD. Twenty-nine patients with COPD were enrolled. On the basis of a polysomnography, they were divided in 2 groups: NREM desaturators (NREM Des ) if they spent more than 10% of NREM sleep time with SpO 2 < 90%, otherwise non desaturators (NREM NoDes ). Serum S100b concentration was measured on awakening as a marker of cerebral lesions. Quadriceps peak twitch (TwQ) was measured by femoral nerve stimulation and voluntary quadriceps strength during isometric maximal voluntary contractions (QMVC), respectively. Level of voluntary activation (LOA) and cortical motor output (VA cortical ) were assessed by interpolated twitches and magnetic stimulation of motor cortex, respectively. Serum S100b was higher in NREM Des ( p < 0.05). In addition, LOA and VA cortical were both reduced in NREM Des ( p < 0.05). However, there were no differences in TwQ and QMVC between the two groups of patients. Higher serum S100b was consistent with higher cerebral lesions in patients with NREM sleep desaturation, which may explain the reduced voluntary activation and cortical output. Surprisingly, QMVC was not different between the NREM Des and NREM NoDes groups, suggesting compensatory mechanism(s) to ensure comparable muscle strength despite motor cortex alteration.

Impaired Quadriceps Rate of Torque Development and Knee Mechanics After Anterior Cruciate Ligament Reconstruction With Patellar Tendon Autograft

Background: Rate of torque development (RTD) measures the ability of a muscle to produce torque quickly. Decreased quadriceps RTD may impair performance of sporting tasks after surgery. Currently, little is known about variations in quadriceps RTD between anterior cruciate ligament (ACL)–reconstructed and noninjured limbs. Purpose: To determine the differences in RTD of the quadriceps, the rate and timing of knee extensor moment (KEM) development, and knee flexion excursion during running after ACL reconstruction with patellar tendon autograft. Study Design: Cross-sectional study; Level of evidence, 3. Methods: This study involved 21 patients (11 female) 6 months after ACL reconstruction with patellar tendon autograft (median [IQR]: age, 18 [16-20] years; mass, 68.18 [61.34-75] kg; height, 1.74 [1.66-1.78] m). Patients performed four 5-second maximal voluntary isometric strength trials of both limbs on an isokinetic dynamometer. RTD was calculated as the mean slope of the torque-time curve between 20% and 80% of total time to peak torque. Then, patients underwent 3-dimensional motion analysis while running on an instrumented treadmill at a self-selected running speed (mean ± SD, 2.68 ± 0.28 m/s). The rate of knee extensor moment (RKEM) was calculated as the mean slope of the moment curve between 10% and 30% of stance phase. Between-limb comparisons were determined with a paired t test for peak KEM, RKEM, knee flexion excursion during 10% to 30% of stance, and time to generate KEM. Results: In the reconstructed limb, deficits in the peak rate of quadriceps torque development compared with the noninjured limb existed both isometrically (RTD, 257.56 vs 569.11 Nm/s; P < .001) and dynamically (RKEM, 16.47 vs 22.38 Nm/kg·m·s; P < .001). The reconstructed limb also generated a KEM later in the stance phase compared with the noninjured limb (11.37% vs 9.61% stance; P < .001) and underwent less knee flexion excursion (15.5° vs 19.8°; P < .001). Conclusion: After ACL reconstruction with patellar tendon autograft, patients have lower RTD and RKEM in the reconstructed limb. Deviations in RTD and the timing of the KEM can change the way the knee is loaded and can potentially increase injury risk and future development of posttraumatic osteoarthritis. Rehabilitation should consider exercises designed to improve RTD and prepare the limb for the demands of sport performance.

Association of regional muscle strength with mortality and hospitalisation in older people.

the association between muscular strength, mortality and hospitalisation with ageing can change depending on sex and the body region analysed (e.g. upper and lower limb muscles). to determine the effect of measuring lower and upper extremities muscular strength on the relationship between strength, mortality and hospitalisation risk in elder men and women. a population-based cohort study using data from the Toledo Study for Healthy Aging (TSHA). a Spanish population sample of 1,755 elders aged ≥65 years participated in this study. Upper (handgrip and shoulder) and lower limbs (knee and hip) maximal voluntary isometric strength was obtained using standardised techniques and equipment. Cox proportional hazards model was used to examine mortality and hospitalisation over 5.5 and 3 years of follow-up, respectively. after adjustment for potential confounding factors, including co-morbidities and BMI, hazard ratio of death and hospitalisation was significantly lower in the stronger women and men, but showing regional- and sex-specific differences. That is shoulder, knee and hip muscle regions in women and handgrip and shoulder in men (all P < 0.05). There was a cumulative effect of measuring several muscle strengths over the risk of health events (P < 0.05), so that mortality hazard ratio increased by 45% in women and 25% in men per muscular strength (shoulder, grip, knee and hip) in the weaker strength quartile increase (P < 0.01). regional muscle strength is a predictor of medium-term mortality and hospitalisation in elder men and women. Multiple strength measures including lower and upper body limb muscles are better predictors than a single strength measurement.

Normative static grip strength of population of Turkey, effects of various factors and a comparison with international norms

Normative data are of importance in ergonomics and clinical settings. Applying normative data internationally is questionable. To this end, this study aimed to establish gender- and age-specific reference values for static (isometric) hand grip strength of normal population of Turkey with special regard to occupational demand, and compare them with the international norms. The secondary aims were to investigate the effects of gender, age-group, weight-group, job-group, hand and several anthropometric variables on static grip strength. A sample of 211 (128 male and 83 female) volunteers aged between 18 and 69 with various occupations participated in the study. Grip strength data were collected using a Jamar dynamometer with standard testing position, protocol and instructions. The mean and std deviation of maximum voluntary static grip strength values (in N) for dominant and non-dominant hands respectively were 455.2 ± 73.6 and 441.5 ± 72.6 for males, and 258 ± 46.1 and 246.2 ± 49.1 for females. The mean female strength was about 57% of the mean male strength value for both dominant and non-dominant hands. There was a curvilinear relationship of grip strength to age, significant differences between genders, hands, and some age-groups, and a correlation to height, body-mass, BMI and hand dimensions depending on the gender. The comparisons with the norms of other world populations indicate that there are cross-national grip strength variations among some nations but not all.

Relación entre proteínas carboniladas y factor necrótico tumoral alfa con fuerza muscular en mujeres jóvenes y mayores: estudio exploratorio

IntroductionIt has recently been proposed that there is a close relationship between oxidative stress and low-grade chronic inflammation. Both processes have been related separately to muscle function in older adults (OA). Nevertheless, it still has not been determined if this relationship is present particularly in OA. The objective of this study was to determine the relationship between the plasma levels of TNF-α and carbonyl proteins (CP) and muscle strength in a group of young and older women. MethodsAn exploratory study was conducted on 13 older and 8 young women, in whom the plasma levels of CP and TNF-α were measured. Muscle strength was measured by handgrip test, quadriceps voluntary maximal isometric strength, arm curl, and the 30 second sit to stand test. ResultsThere were no differences in the plasma levels of CP and TNF-α between the groups, but there was relationship between the biomarkers only in the OA group. A non-linear relationship was observed between CP and quadriceps voluntary maximal isometric strength only in the OA group (R2=36.2; P=.038). For TNF-α there were no significant association with any of the applied tests. ConclusionsThere is an association between CP and quadriceps voluntary maximal isometric strength only in the OA group, which could indicate a deleterious action of oxidative stress on muscle function, particularly in aging.

Low-intensity eccentric contractions of the knee extensors and flexors protect against muscle damage.

This study investigated the magnitude and duration of the protective effect of low-intensity eccentric contractions (LowEC) against damage induced by maximal eccentric contractions (MaxEC) of the knee flexors (KF) and extensors (KE). Young men were assigned to 8 experimental groups and 2 control groups (n = 13/group); the experimental groups performed LowEC of KF or KE 2 days (2d), 1 week (1wk), 2 weeks (2wk), or 3 weeks (3wk) before MaxEC, while the control groups performed MaxEC of KF or KE without LowEC. The 2d, 1wk, 2wk, and 3wk groups performed 30 LowEC of KF or 60 LowEC of KE with a load of 10% of maximal voluntary isometric contraction strength on a resistance-training machine, and all groups performed 30 MaxEC of KF or 60 MaxEC of KE on an isokinetic dynamometer. Several muscle damage markers were measured from before to 2 days after exercise (LowEC) or from before to 5 days after exercise (MaxEC). No significant changes in any variables were evident after LowEC. The changes in all variables after MaxEC were smaller (P < 0.05) for the 2d and 1wk groups (e.g., peak creatine kinase activity: 1002 ± 501 IU/L; peak muscle soreness: 13 ± 5 mm) than for the control group (peak creatine kinase activity: 3005 ± 983 IU/L; peak muscle soreness 28 ± 6 mm) for both KE and KF. There were no significant differences between the 2d and 1wk groups or among the 2wk, 3wk, and control groups. These results show that LowEC provided 30%-66% protection against damage induced by MaxEC of KF and KE, and the protective effect lasted 1 week.

Caffeine's Ergogenic Effects on Cycling: Neuromuscular and Perceptual Factors.

Caffeine improves endurance exercise performance, but its ergogenic mechanism(s) remain unclear. This investigation sought to examine the effects of caffeine on perceptual and physiological responses to endurance exercise. Two experiments were performed. In study A, 14 participants were tested. Maximal voluntary strength (MVC) and motor-unit recruitment (%ACT) of the knee extensors and elbow flexors were tested before and 60 min after ingestion of a 5-mg·kg⁻¹ dose of caffeine or placebo and after completion of 40 min of exercise (30 min of submaximal leg or arm cycling followed by a 10-min time-trial performance). Muscle pain, RPE, and cardiorespiratory variables were assessed throughout. To determine the effects of caffeine on muscle pain and RPE during high-intensity exercise, a second study (study B) was performed. Twelve participants exercised at 95% of their gas exchange threshold (GET) and at 70% of the difference between their GET and VO(2peak) (70%Δ) after caffeine and placebo ingestion. Compared to placebo, caffeine improved MVC (6.3%, P = 0.014) and %ACT (5.5%, P = 0.013) in the knee extensors, but not the elbow flexors, and reduced muscle pain (P < 0.05) and RPE (P < 0.05) during both submaximal cycling modalities. Caffeine ingestion improved time-trial performance during leg cycling (4.9% ± 6.5%, P = 0.03), but not arm crank cycling (2.1% ± 8.2%, P = 0.28), but the effect on pain and RPE was eliminated. Caffeine ingestion had no effect on pain or RPE during cycling at 95% GET and 70%Δ. Our results suggest that augmented strength and motor-unit recruitment, rather than reductions in pain and effort, may underlie caffeine's ergogenic effect on endurance exercise.

Caffeine-induced increase in voluntary activation and strength of the quadriceps muscle during isometric, concentric and eccentric contractions.

This study investigated effects of caffeine ingestion (8 mg/kg) on maximum voluntary torque (MVT) and voluntary activation of the quadriceps during isometric, concentric and eccentric contractions. Fourteen subjects ingested caffeine and placebo in a randomized, controlled, counterbalanced, double-blind crossover design. Neuromuscular tests were performed before and 1 h after oral caffeine and placebo intake. MVTs were measured and the interpolated twitch technique was applied during isometric, concentric and eccentric contractions to assess voluntary activation. Furthermore, normalized root mean square of the EMG signal was calculated and evoked spinal reflex responses (H-reflex evoked at rest and during weak isometric voluntary contraction) as well as twitch torques were analyzed. Caffeine increased MVT by 26.4 N m (95%CI: 9.3-43.5 N m, P = 0.004), 22.5 N m (95%CI: 3.1-42.0 N m, P = 0.025) and 22.5 N m (95%CI: 2.2-42.7 N m, P = 0.032) for isometric, concentric and eccentric contractions. Strength enhancements were associated with increases in voluntary activation. Explosive voluntary strength and voluntary activation at the onset of contraction were significantly increased following caffeine ingestion. Changes in spinal reflex responses and at the muscle level were not observed. Data suggest that caffeine ingestion induced an acute increase in voluntary activation that was responsible for the increased strength regardless of the contraction mode.

Older men are more fatigable than young when matched for maximal power and knee extension angular velocity is unconstrained.

The underlying factors related to the divergent findings of age-related fatigue for dynamic tasks are not well understood. The purpose here was to investigate age-related fatigability and recovery between a repeated constrained (isokinetic) and an unconstrained velocity (isotonic) task, in which participants performed fatiguing contractions at the velocity (isokinetic) or resistance (isotonic) corresponding with maximal power. To compare between tasks, isotonic torque-power relationships were constructed prior to and following both fatiguing tasks and during short-term recovery. Contractile properties were recorded from 9 old (~75 years) and 11 young (~25 years) men during three testing sessions. In the first session, maximal power was assessed, and sessions 2 and 3 involved an isokinetic or an isotonic concentric fatigue task performed until maximal power was reduced by 40 %. Compared with young, the older men performed the same number of contractions to task failure for the isokinetic task (~45 contractions), but 20 % fewer for the isotonic task (p < 0.05). Regardless of age and task, maximal voluntary isometric contraction strength, angular velocity, and power were reduced by ~30, ~13, and ~25 %, respectively, immediately following task failure, and only isometric torque was not recovered fully by 10 min. In conclusion, older men are more fatigable than the young when performing a repetitive maximal dynamic task at a relative resistance (isotonic) but not an absolute velocity (isokinetic), corresponding to maximal power.

Postoperative impairment of motor function at train-of-four ratio ≥0.9 cannot be improved by sugammadex (1 mg kg−1)

A train-of-four ratio (TOFR) ≥0.9 measured by quantitative neuromuscular monitoring is accepted as an indication of sufficient neuromuscular recovery for extubation, even though many postsynaptic acetylcholine receptors may still be inhibited. We investigated whether antagonism with sugammadex after spontaneous recovery to TOFR≥0.9 further improves muscle function or subjective well-being. Following recovery to TOFR≥0.9 and emergence from anaesthesia, 300 patients randomly received either sugammadex 1.0 mg kg(-1) or placebo. Fine motor function (Purdue Pegboard Test) and maximal voluntary grip strength were measured before and after surgery (before and after test drug administration). At discharge from the postanaesthesia care unit, well-being was assessed with numerical analogue scales and the Quality-of-Recovery Score 40 (QoR-40). Patients' fine motor function [6 (sd 4) vs 15 (3)pegs(30 s)(-1), P<0.05] and maximal voluntary grip strength (284 (126) vs 386 (125) N, P<0.05) were significantly lower after anaesthesia compared with the pre-anaesthesia baseline. After sugammadex or placebo, motor function was significantly improved in both groups but did not reach the preoperative level. There was no difference between groups at any time. Global well-being was unaffected (QoR-40: placebo, 174 vs 185; sugammadex, 175 vs 186, P>0.05). Antagonizing rocuronium at TOF≥0.9 with sugammadex 1.0 mg kg(-) (1) did not improve patients' motor function or well-being when compared with placebo. Our data support the view that TOFR≥0.9 measured by electromyography signifies sufficient recovery of neuromuscular function. The trial is registered at ClinicalTrials.gov (NCT01101139).

Caffeine-induced Increase In Neural Activation And Strength Of The Quadriceps During Isometric And Dynamic Contractions

Caffeine is usually consumed in the form of tea, coffee, chocolate products as well as carbonated beverages and is one of the most popular drugs [1]. There is evidence that caffeine increases endurance and short-term, high-intensity exercise performance [2]. However, the effect of caffeine on maximal voluntary contraction strength and neural activation during different contraction modes is less clear. PURPOSE: Therefore, this study investigated effects of caffeine ingestion (8 mg/kg) on maximum voluntary torque (MVT) and neural activation of the quadriceps muscle during isometric, concentric and eccentric contractions. METHODS: Fourteen subjects ingested caffeine and placebo in a randomized, controlled, counterbalanced, double-blind crossover design. Neuromuscular tests were performed before and 1 h after oral caffeine and placebo intake. MVTs were measured and the interpolated twitch technique was applied during isometric, concentric and eccentric contractions to assess voluntary activation. Furthermore, normalized root mean square of the EMG signal was calculated and evoked spinal reflex responses (H-reflex evoked at rest and during weak isometric voluntary contraction) as well as contractile properties of the quadriceps were analyzed. RESULTS: Caffeine increased MVT by 26.4 N•m (+13.7%, 95%CI: 9.3-43.5 N•m, P = 0.004), 22.5 N•m (+13.9%, 95%CI: 3.1-42.0 N•m, P = 0.025) and 22.5 N•m (+11.7%, 95%CI: 2.2-42.7 N•m, P = 0.032) for isometric, concentric and eccentric contractions. Strength enhancements were associated with increases in voluntary activation. Isometric explosive voluntary strength and neural activation at the onset of contraction were significantly increased following caffeine ingestion. Changes in spinal reflex responses and contractile properties were not observed. CONCLUSIONS: Data suggest that caffeine ingestion induced acute neural adaptations that were responsible for the increased strength and neural activation regardless of the contraction mode. The results indicate that strength gains were due to alterations of excitability at the supraspinal site rather than changes in spinal excitability. REFERENCES 1. Harland BF, Nutrition. 16:522-6, 2000. 2. Burke LM, Appl Physiol Nutr Metab. 33:1319-34, 2008.

Does The Weaker Limb Limit Physical Performance In Older Adults?

PURPOSE: The purpose of this study was to examine the relationship of unilateral knee extensor strength asymmetry to physical function in adults at risk of mobility-limitation. METHODS: 30 subjects (75.2±6.9 yr, 167.5±9.0 cm, 74.7±14.0 kg) had their maximal voluntary isometric knee extension strength measured on a dynamometer for each limb. Subject’s percent asymmetry between the strong limb (SL) and weak limb (WL) was calculated. Those with asymmetries >10% were placed in the asymmetrical group (AG, n=14) and those <10% were placed in the symmetrical group (SG, n=16). Physical function was assessed during a timed 400m walk, chair-rise, and stair ascent. It was hypothesized that AG would have a lower level of function that was limited by the weak limb. A multivariate analysis of variance was used to examine differences in strength and performance between groups. Pearson correlations were used to study the relationship between leg strength and physical function. Significance was p<0.05. RESULTS: AG had greater strength asymmetry (22.6±15.8%) than SG (4.3±3.3%, p<0.01), lower WL strength (1.15±0.36 Nm kg-1 vs 1.55±0.43 Nm kg-1, p=0.01), but similar SL strength (1.48±0.30 Nm kg-1 vs 1.63±0.43 Nm kg-1, p=0.30). WL strength was correlated with SL strength (r = 0.90, p<0.01), 400m walk (r = -0.41, p<0.01), chair-rise (r = -0.39, p=0.01), and stair ascent (r = -0.36, p=0.01). SL strength was similarly correlated with 400m walk (r = -0.50, p<0.01), chair-rise (r = -0.40, p=0.01), and stair ascent (r = -0.42, p<0.01). There was no difference in physical function between groups (p>0.05) nor were there correlations between degree of asymmetry and physical function (p>0.05). CONCLUSION: Strength asymmetry did not limit physical function in this sample of older adults because the relative strength of each limb was more closely related to performance than the difference in strength between them, and, within an individual WL and SL strength were highly correlated. Leg strength criteria are often used to evaluate the risk of falls and mobility loss in older adults and it is currently not clear how strength asymmetry affects these relationships. Supported by: NIH Grant 1R15 A6040700-01A1

Reliability and validity of a custom-made instrument including a hand-held dynamometer for measuring trunk muscle strength.

Measuring isometric strength is necessary in many areas of health and sport. However, trunk muscles have some particular characteristics that make them difficult to evaluate with simple, inexpensive instruments. To evaluate the reliability and validity of an instrument constructed with a hand-held dynamometer and a metallic structure (HHD+S) for measuring maximum isometric voluntary trunk muscle strength. Maximum isometric voluntary trunk muscle strength (extension, flexion and lateral flexion) was measured in 20 healthy individuals using the custom-made instrument (HHD+S) and the gold standard Back-Check (BC). The results showed that the two instruments had high and similar intra-subject reliability. The validity of the HHD+S was demonstrated by the high Pearson coefficient correlation between the two instruments (r ⩾ 0.78). Given the good trial reliability and the close correlation between the two instruments, we believe that the use of a hand-held dynamometer together with the custom-made metallic structure (HHD+S) allows an evaluation of the maximum isometric voluntary trunk muscle strength to be made, that is very similar in quality, accuracy and reliability to the BC.

Excess Body Weight Affects Viscoelastic Properties of Triceps Surae in Older Women

Aging, inactivity, and excess body weight may negatively affect the passive work absorbing capacity of human skeletal muscle. The objective of this study was to examine the influence of excess body weight on the viscoelastic properties of the triceps surae in older women. Twenty-five women, 65-80 yr, were separated into normal weight (NW, BMI 蠄 24.9 kg m-2, n = 11) and overweight groups (OW, BMI 蠅 25.0 kg m-2, n = 14). Resistive torque of the triceps surae was recorded on an isokinetic dynamometer by passively moving the ankle from a plantarflexed to dorsiflexed position. Stiffness was calculated as the slope of the passive torque vs. position curve from 1.57 – 1.48 rad (90 – 85 deg) of dorsiflexion, and work absorption was calculated as the area under the curve. Maximal voluntary isometric strength of the triceps surae was recorded, then participants walked at maximal speed on an instrumented treadmill while muscle activation was recorded by electromyography (EMG). Stiffness was higher in NW (40.0 ± 15.7 Nm rad-1) than in OW (26.4 ± 12.7 Nm rad-1, p = 0.032), as was stiffness per kg (0.70 ± 0.28 vs. 0.37 ± 0.16 Nm rad-1 kg-1, p = 0.002). Work absorption was not statistically different between NW (0.48 ± 0.29 Nm rad) and OW (0.36 ± 0.16 Nm rad, p = 0.31) nor when expressed per kg (0.0083 ± 0.0052 vs. 0.0050 ± 0.0023 Nm rad kg-1, p = 0.078). Stiffness per kg was correlated to strength (r = 0.66, p < 0.001), peak vertical ground reaction force during walking (r = 0.72, p < 0.001), and EMG (r = -0.40, p = 0.046) with similar relationships for work absorption. OW older women have low stiffness of triceps surae, which may impair ability to absorb and return work during stretch-shortening cycles. Low stiffness in OW may limit propulsive forces during walking and necessitate greater muscle activation for active force generation. Supported by NIH L30TR000588-02

Effects of Quercetin on Muscle Function during IL‐6‐induced Cancer Cachexia

Cachexia is a devastating wasting condition that occurs secondary to chronic diseases including AIDS, COPD, and cancer. Characterized by a loss of body weight including adipose tissue and muscle atrophy, 20-50% of cancer patients are affected with an annual mortality rate of 80%. It is known that IL-6 drives cachexia in the male ApcMin/+ mouse. Quercetin, an anti-inflammatory flavonoid, has been shown to attenuate symptoms of cachexia. There is evidence that this occurs through the IL-6 pathway; however, this has not been directly tested. The purpose of this study was to determine whether quercetin could attenuate muscle function loss caused by systemic IL-6 over-expression in female ApcMin/+mice. Our hypothesis was that IL-6 over-expression would exacerbate muscle strength and endurance decrements, which would be attenuated by quercetin supplementation in cachectic female ApcMin/+ mice. Female ApcMin/+ mice (n=24) were divided into 4 groups at 15 weeks of age: 1) Control 2) IL-6 electroporation (50 μg plasmid in 50 μl PBS), 3) daily quercetin gavage (75 mg/kg body weight), 4) IL-6 electroporation + quercetin. Functional testing including voluntary grip strength, run to fatigue, and DEXA scan were performed before treatment and at time of sacrifice. Quercetin attenuated grip strength loss compared to control mice (p=0.02); however, this effect was abolished by the overexpression of IL-6 in addition to quercetin. Quercetin was unable to rescue muscle endurance loss. Further analysis will determine the pathways by which quercetin and IL-6 exert their effects on muscular strength and endurance in cachectic female ApcMin/+mice.

Movement pattern training improves function in people with intra-articular, pre-arthritic hip disease: Preliminary data

Movement pattern training improves function in people with intra-articular, pre-arthritic hip disease: Preliminary data