One-legged bicycling as an assessment tool for patients with stroke

OBJECTIVE: To assess whether one-legged bicycling correlates with muscle strength and thereby could work as an outcome measure for persons with stroke. METHODS: The study comprised 29 men (age 35-65) with a first occurrence of stroke 6-35 months earlier. Each leg was evaluated separately. A ramp protocol was used (10 W/min), with continuous recording of the ventilatory uptake (Vo(2)) and heart rate. An isokinetic dynamometer was used to assess strength and endurance. Enzyme assays were performed on muscle biopsy samples. RESULTS: The peak isometric strength and isokinetic strength of the paretic leg correlated with the max. W on the bicycle. The oxidative enzyme citrate synthase correlated with the workload for both legs on the bicycle and lactate dehydrogenase correlated with peak isometric strength in both legs. CONCLUSIONS: The one-legged bicycle exercise test can be used to assess endurance in persons with a previous stroke as it correlates with dynamometer testing and muscle biopsies.     

Inter-rater and test/retest reliabilities of the isokinetic measurements: assessing strength and endurance of the trunk muscles in two different protocols for able-bodied and post-stroke hemiparesis

Background Stroke represents the largest cause of chronic disability resulting in muscle weakness and instability in the trunk muscles. Despite the reliable measures from isokinetic devices for upper/lower limb muscles, there is a lack of measures for trunk muscles in post-stroke hemiparesis.

Objectives To investigate the reliability of the strength and endurance measures from an isokinetic dynamometer for able-bodied and post-stroke hemiparesis people.

Methods The measures were taken from both groups (control/hemiparesis) performing antagonistic movements (flexion/extension) during different protocols (seated-compressed and semi-standing) to assess strength (60º/s) and endurance (120º/s). The intra-class correlation coefficient (ICC) and limits of agreement (LOA) defined the quality and magnitude of reliability on the measurements plotted with 95% confidence interval (95% CI) by Bland–Altman method.

Results ICC ranged from 0.58 to 0.99, with few ICC values classified as moderate when repeated by raters during test and a single value during retest. The total work was the only variable to present LOA higher than the limits.

Conclusion Results indicate acceptable reliability, in two different protocols, confirming the repeatability of the isokinetic measures for trunk muscles in able-bodied and post-stroke hemiparesis.     

Does training with traditionally presented and virtually simulated tasks elicit differing changes in object interaction kinematics in persons with upper extremity hemiparesis?

Abstract

Objective:

To contrast changes in clinical and kinematic measures of upper extremity movement in response to virtually simulated and traditionally presented rehabilitation interventions in persons with upper extremity hemiparesis due to chronic stroke.

Design:

Non-randomized controlled trial.

Setting:

Ambulatory research facility.

Participants:

Subjects were a volunteer sample of twenty one community-dwelling adults (mean age: 51?±?12 years) with residual hemiparesis due to stroke more than 6 months before enrollment (mean: 74?±?48 months), recruited at support groups. Partial range, against gravity shoulder movement and at least 10° of active finger extension were required for inclusion. All subjects completed the study without adverse events.

Interventions:

A 2 weeks, 24-hour program of robotic/virtually simulated, arm and finger rehabilitation activities was compared to the same dose of traditionally presented arm and finger activities.

Results:

Subjects in both groups demonstrated statistically significant improvements in the ability to interact with real-world objects as measured by the Wolf Motor Function Test (P?=?0.01). The robotic/virtually simulated activity (VR) group but not the traditional, repetitive task practice (RTP) group demonstrated significant improvements in peak reaching velocity (P?=?0.03) and finger extension excursion (P?=?0.03). Both groups also demonstrated similar improvements in kinematic measures of reaching and grasping performance such as increased shoulder and elbow excursion along with decreased trunk excursion.

Conclusions:

Kinematic measurements identified differing adaptations to training that clinical measurements did not. These adaptations were targeted in the design of four of the six simulations performed by the simulated activity group. Finer grained measures may be necessary to accurately depict the relative benefits of dose matched motor interventions.     

Effects of body orientation on maximum voluntary arm torques

Introduction: Increased reliance on bulbospinal motor systems has been implicated in individuals with chronic stroke during maximum voluntary arm joint torque generation. Methods: Maximum isometric single‐joint and multi‐joint arm strength was observed in two body orientations (sitting and supine) while maintaining identical head/neck/trunk/extremity joint configurations in order to identify bulbospinal contributions to maximum joint torque generation in 11 individuals with stroke and 10 individuals without stroke. Results: During sitting, shoulder flexion was greater for both groups, whereas shoulder extension and elbow flexion, part of the “flexion synergy,” were greater only in individuals with stroke. Conclusions: Body orientation influenced isometric arm strength, notably the constituents of flexion synergy in individuals with stroke, suggesting bulbospinal motor pathway involvement. From a practical perspective, clinical evaluation of single joint strength in the supine position may underestimate strength available during activities of daily living that are performed in an upright orientation. Muscle Nerve, 2011     

Muscle architecture and torque production in stroke survivors: an observational study

Objective: Spasticity poststroke leads to muscle weakness and soft tissue contracture, however, it is not clear how muscle properties change due this motor neural disorder. The purpose was to compare medial gastrocnemius muscle architecture and mechanical properties of the plantarflexor muscles between stroke survivors with spasticity and healthy subjects.

Methods: The study included 15 stroke survivors with ankle spasticity and 15 healthy subjects. An isokinetic dynamometer was used for the evaluation of maximal isometric plantarflexor torque and images of the medial gastrocnemius muscle were obtained using ultrasonography. Images were collected at rest and during a maximum voluntary contraction.

Results: The affected limb showed reduced fascicle excursion (0.9 ± 0.7 cm), shorter fascicle length, and reduced muscle thickness (0.095 ± 0.010% of leg length and 1.18 ± 0.20 cm, at rest) compared to contralateral (1.6 ± 0.4 cm, 0.106 ± 0.015% of leg length and 1.29 ± 0.24 cm, respectively) and to healthy participants (1.8 ± 0.7 cm, 0.121 ± 0.019% of leg length and 1.43 ± 0.22 cm, respectively). The contralateral limb showed lower force (between 32 and 40%) and similar architecture parameters compared to healthy participants.

Conclusion: The affected limb had a different muscle architecture that appears to result in lower force production. The contralateral limb showed a decrease in force compared to healthy participants due to the other neural impairments than muscle morphology. Spasticity likely leds to adaptations of muscle architecture in the affected limb and in force reductions in both limbs of stroke survivors.     

The biomechanical investigation of the relationship between balance and muscular strength in people with chronic stroke: a pilot cross-sectional study

Background: Impaired balance and weak muscle strength are common deficits associated with stroke. Limited research has examined the relationship between balance and strength in people post-stroke.

Objective: To investigate the association between balance and muscular strength in people post-stroke.

Methods: A total of 11 people with chronic stroke, who were community dwelling and ambulatory, completed balance and strength assessments. A computerized dynamic posturography system was used for Limits of Stability (LOS) test, Sit-to-Stand (STS) test, and the Modified Clinical Test of Sensory Interaction on Balance (mCTSIB). Additionally, a computerized dynamometer was used to assess the isometric muscle strength of flexion/extension in the core (the trunk) and the leg (the hip, knee, and ankle). Pearson correlation analysis was used to investigate the relationship between balance and muscle strength measurements.

Results: Endpoint excursion (EPE) (r = .646; p < 0.032) and maximum excursion (MXE) (r = .613; p < 0.045) of LOS test were positively correlated with core and leg strength (C&L). Specifically, both EPE (r = ?.792; p < 0.004) and MXE (r = ?.623; p < 0.041) in backward direction had strong correlations with C&L. Core strength also showed a positive correlation with EPE of LOS test (r = .636; p < 0.035) while the composite leg strength did not. Lastly, STS and mCTSIB tests did not demonstrate significant associations with muscle strength.

Conclusions: The results indicate that the C&L have a strong relationship with the ability to shift body weight in multiple directions, particularly backward, among people post-stroke. However, static balance and STS performance do not appear to be related to muscle strength.     

Upper extremity function and its relation with hand sensation and upper extremity strength in patients with multiple sclerosis

The purpose of this study was to investigate the relationships between the upper extremity functions, upper extremity strength and hand sensation in patients with Multiple Sclerosis (MS). Twenty-two patients with MS (mean age: 38.5 ± 8.31 years, median Expanded Disability Status Scale (EDSS): 2) and 10 healthy subjects were included. Upper extremity function was measured with the Nine-hole peg test, upper extremity strength (shoulder flexion-abduction, elbow flexion, pinch and grip) with hand-held dynamometer, hand grip dynamometer and manual pinch meter, threshold of light touch-pressure with Semmes-Weinstein monofilament, duration of vibration with 128-Hz frequency tuning fork, and distance of two-point discrimination with an aesthesiometer. Strength and functional level of the upper extremity, light touch-pressure, two-point discrimination, vibration sensations of the hand were lower in patients with MS compared with healthy controls (p < 0.05). Light touch-pressure sensation of thumb and index fingers, two-point discrimination of index finger and elbow flexion strength were found to be related with upper extremity function in patients with MS (p< 0.05). These results indicate that the hand sensation, upper extremity strength and function were affected in MS patients. Additionally upper extremity functions seem to be related with light touch-pressure and two-point discrimination sensations of the hand and elbow flexion strength. Upper extremity strengthening and sensorial training of the hand may contribute to the upper extremity function in patients with MS.     

Impaired mechanical properties of Achilles tendon in spastic stroke survivors: an observational study

Background: The spasticity could lead to decreased functional capacity and changes in musculoskeletal tissue.

Objective: To compare the Achilles tendon properties between the affected and contralateral limbs of participants with spasticity due to stroke and the healthy subjects.

Methods: Fifteen individuals with ankle spasticity due to stroke and 15 healthy subjects were recruited. Maximal isometric ankle joint torque was obtained with an isokinetic dynamometer, and an ultrasound was used to determine tendon length, tendon cross-sectional area, and the medial gastrocnemius myotendinous junction displacement. The Achilles tendon strength, displacement, stress, strain, stiffness, and Young’s modulus were obtained during a maximum voluntary isometric plantarflexion contraction.

Results: There were no differences between Achilles tendon length among participants. Both limbs of participants with stroke showed reduced tendon cross-sectional area (~18%) compared to healthy limb. The affected limb showed decreased tendon strength (686 ± 293.3 N), displacement (10.6 ± 1.7 mm), Young’s modulus values (849 ± 235.6 MPa), and lower stiffness (196.6 ± 67.6 N/mm) compared to the contralateral limb (strength, 1357.1 ± 294.8 N; displacement, 15.2 ± 5.5 mm; Young’s modulus, 1431.8 ± 301.9 MPa; stiffness, 337.5 ± 98.1 N/mm) and to the healthy limb. The contralateral limb also showed decreased tendon strength (~26.2%) and stiffness (~21.5%) compared to the healthy group.

Conclusion: There is a decrement in Achilles tendon morphological and mechanical properties of the affected limb in individuals with spasticity due to stroke. The contralateral limb had a thinner tendon more compliant likely to physical activity reduction.     

Pilot randomized controlled trial to assess a physical therapy program on upper extremity function to counteract inactivity in chronic stroke

Background: In chronic stroke, feasible physical therapy (PT) programs are needed to promote function throughout life.

Objective: This randomized controlled pilot trial investigated the feasibility and effect of a PT program composed of strengthening exercises with elastic bands and bimanual functional training, with clearly defined doses based on the rate of perceived exertion (Borg scale), to counteract inactivity in chronic stroke.

Methods: Fifteen subjects > 6 month post-stroke were randomized to three-month of UE function training (UE group), or to lower extremity function training (LE group). At baseline (T0), post-intervention (T1) and three-month follow-up (T2) assessment included the Fugl-Meyer Assessment scale (FMA), Wolf Motor Function test (WMFT), grip strength, and muscle tone. Feasibility was also evaluated.

Results: The mixed-model ANOVAs revealed a significant interaction between the time and group factors for FMA (p < .001) and WMFT (p = .009). The UE group improved upper extremity function and motor recovery significantly more than the LE group. There was no significant interaction between treatment group and change in grip strength over time (p = .217). No between-group differences (p > .05) were found in muscle tone. In the UE group, the attendance rate was ≥85% for 71.4% of subjects and 85.7% showed high satisfaction. No adverse events were recorded. After treatment, adherence to the program was higher in the UE group.

Conclusions: The suggested PT program may be useful to improve the paretic UE function and motor recovery in chronic stroke. Moreover, it may be helpful to facilitate lifelong active involvement of stroke subjects in exercise.     

Handwriting performance versus arm forward reach and grasp abilities among post-stroke patients,a case-control study

Background: Evidence-based studies regarding deficits in handwriting performance relative to hand reaching and grasping after a stroke are lacking.

Objective: To evaluate the extent of damage to handwriting skills compared to arm reach and grasp task among post-stroke patients.

Methods: Eighteen patients and 19 healthy subjects were recruited to this case-control study. Patients were evaluated 15.2 days (±6.5) after the stroke using a Computerized Penmanship Evaluation Tool, surface Electromyography and Fugl-Meyer assessment. This study compared motor deficits in hand reaching and grasping and in handwriting between stroke patients and healthy subjects. Damage to handwriting performance relative to hand reaching and grasping skills was also evaluated.

Results: Significant differences were found between groups in handwriting performance (p < 0.05). The performance of the trapezius, biceps, and triceps muscles can predict 63.5% of the variance in the ability to write a short sentence (p < 0.023). Pen pressure can predict 74.9% of the hand motor performance from Fugl-Meyer assessment (p < 0.05). Handwriting was more damaged than was the pattern of activation of the proximal muscles of the shoulder and arm (p < 0.05). FM scores were highly, negatively correlated with the in-air writing time across tasks (r = ?0.819, p < 0.004).

Conclusions: This study confirms the clinical observation that dexterity skills are more damaged than are arm forward reach after a stroke. However, these differences in motor performance were not significant in mildly disabled patients, demonstrating the feasibility of handwriting rehabilitation in these patients. Therefore, we modestly recommend focusing on handwriting rehabilitation of the hemiparetic upper extremity in mildly impaired patients after a stroke.     

Skeletal muscle changes following stroke: a systematic review and comparison to healthy individuals

Background: Despite extensive study of the impact of stroke on muscle and functional performance, questions remain regarding the extent to which changes are due to the neurological injury vs. age-related loss of morphology and force production.

Objectives: To synthesize available evidence describing post-stroke changes in lower extremity muscle size and strength compared to healthy adults.

Methods: Scientific literature was searched up to April 2016 to identify studies that included lower extremity muscle size and strength measures in individuals with chronic stroke. Lower extremity muscle size and strength data from healthy controls were sought for comparison. Relative differences were calculated between paretic, nonparetic, and control limbs.

Results: Fifteen studies with 375 participants (61% male; age = 62 ± 5 years; time since stroke = 60 ± 42 months) were included. The paretic limb exhibited deficits of ~13% in thigh muscle size, ~5% in lower leg muscle size, and ~8% in lean leg mass compared to the nonparetic limb. Paretic plantarflexor and knee extensor strength were 52 and 36% lower, respectively, compared to the nonparetic limb. When compared to age-matched control data, both paretic and nonparetic limbs showed deficits in muscle size and strength.

Conclusions: Age-related differences support the impact of stroke-related sarcopenia as a contributor to hemiparetic muscle dysfunction. Understanding these muscular changes is necessary for designing appropriate exercise interventions aimed at restoring muscle function.     

Cross-sectional study of quadriceps properties and postural stability in patients with chronic stroke and limited vs. non-limited community ambulation

Background: Changes in the paretic-side metabolism post-stroke and quadriceps muscle mechanical properties favour muscle wasting, affecting postural instability and walking impairment. Further clarification is needed in subjects post-stroke who show limited or non-limited community ambulation.

Objectives: To analyze between-limb differences in quadriceps muscle thickness, strength and thigh cutaneous temperature, as well as investigate postural stability in subjects with chronic stroke and limited vs. non-limited community ambulation and compared against healthy controls.

Methods: In this controlled cross-sectional study, 26 participants with chronic hemiparesis post-stroke (divided in a slow gait group (SG<0.8 m/s) (n = 13) and a fast gait group with full community ambulation speed (FG≥0.8 m/s)) and 18 healthy people were recruited. Thigh surface temperature, rectus femoris (RF) and vastus intermedius (VI) muscles thickness, quadriceps’ isometric maximal voluntary contraction and postural stability were measured.

Results: The SG presented significantly lower RF (P = .019) and VI (P = .006) muscle thickness, less peak force (P < .001) and lower temperature (P = .002) in the paretic vs the non-paretic limb. The FG showed significantly lower VI thickness (P = .036) and peak force (P < .001) in the paretic vs the non-paretic limb. Regarding balance, all indices were worse in the SG versus the FG and CG.

Conclusions: Subjects of the FG, despite showing full community ambulation speed, had less quadriceps strength and VI muscle thickness but not RF muscle wasting in the paretic limb. The paretic VI muscle wasting may be an important factor to reach normal walking. The SG showed between-limb differences in all the studied variables and the worst postural stability.     

Feasibility and reliability of measuring strength, sprint power, and aerobic capacity in athletes and non-athletes with cerebral palsy

Aim The aim of this study was to analyse the feasibility and reliability of the tests used to determine muscle strength, sprint power, and aerobic capacity in athletes and non‐athletes with cerebral palsy (CP). Methods Twenty individuals with spastic CP (four females, 16 males; age range 18–49y; Gross Motor Function Classification System level I, n=15; II, n=5; unilateral CP, n=10; bilateral CP, n=10; athletes, n=12; non‐athletes, n=8) participated in the study. Isometric and isokinetic knee flexor and extensor strength, sprint power, and aerobic capacity were determined, using, respectively an isokinetic dynamometer, a Wingate cycling test, and a graded maximal bicycle exercise test, on three occasions. Intraclass correlation coefficients (ICC), standard error of measurements, and smallest detectable differences (SDD) were calculated. Results The feasibility of the isometric strength test, Wingate test, and graded exercise test was good; the isokinetic strength test was difficult to perform for five participants. The strength parameters showed moderate to good ICCs (isometric, 0.74–0.94; isokinetic, 0.88–0.93) but high SDDs (isometric, 25–45%; isokinetic, 30–45%). Sprint power (ICC 0.98; SDD 24%) and aerobic capacity (ICC 0.98–0.99; SDD 16–21%) showed good ICCs and moderate SDDs. Interpretation All tests, except for the isokinetic strength test, seemed to be feasible for almost all participants. All tests are suitable for evaluating changes in a group; however, only large improvements (16–45%) can be detected when monitoring individual changes.     

Reachable workspace reflects dynamometer‐measured upper extremity strength in facioscapulohumeral muscular dystrophy

Introduction: It is not known whether a reduction in reachable workspace closely reflects loss of upper extremity strength in facioscapulohumeral muscular dystrophy (FSHD). In this study we aimed to determine the relationship between reachable workspace and quantitative upper extremity strength measures. Methods: Maximal voluntary isometric contraction (MVIC) testing of bilateral elbow flexion and shoulder abduction by hand‐held dynamometry was performed on 26 FSHD and 27 control subjects. In addition, Kinect sensor‐based 3D reachable workspace relative surface areas (RSAs) were obtained. Loading (500‐g weight) effects on reachable workspace were also evaluated. Results: Quantitative upper extremity strength (MVIC of elbow flexion and shoulder abduction) correlated with Kinect‐acquired reachable workspace RSA (R = 0.477 for FSHD, P = 0.0003; R = 0.675 for the combined study cohort, P < 0.0001). Progressive reduction in RSA reflected worsening MVIC measures. Loading impacted the moderately weak individuals the most with additional reductions in RSA. Conclusions: Reachable workspace outcome measure is reflective of upper extremity strength impairment in FSHD. Muscle Nerve 52 : 948–955, 2015     

Further observations on forearm flexor weakness in inclusion body myositis

In order to further characterize and provide a possible mechanism for the asymmetrical involvement of forearm muscles in inclusion body myositis (IBM), we measured isometric hand and pinch grip strength, and forearm muscle girth on 15 IBM patients. Forearm muscle strength and girth were significantly greater on the dominant versus nondominant side: mean grip strength, 173.9 vs. 98.8 N; mean pinch strength, 47.6 vs. 29.7 N; and mean forearm girth, 22.5 vs. 19.9 cm. This observation may suggest a role for exercise in delaying the disease progression in IBM. © 1998 John Wiley & Sons, Inc. Muscle Nerve 21:659–661, 1998.     

Robot-Assisted Therapy Combined with Trunk Restraint in Acute Stroke Patients: A Randomized Controlled Study

BackgroundReducing the compensatory mechanism by restraining unnecessary trunk movements may help enhance the effectiveness of robot-assisted therapy.ObjectiveThis study aimed to investigate the effects of robot-assisted therapy in combination with trunk restraint on upper extremity function and on daily activities in patients with acute stroke (≤ 30days of onset).MethodsThirty-six acute stroke patients were randomly assigned to an experimental (n=18) or control (n=18) group. The experimental group performed robot-assisted therapy combined with trunk restraint, while the control group performed only robot-assisted therapy. Both groups were treated for 30 min, 5 days a week, for a total of 3 weeks. The outcome measures included the Fugl-Meyer assessment upper extremity, wolf motor function test, motor activity log, upper extremity muscle strength, and modified Barthel index.ResultsAfter the intervention, both groups showed significant improvements in Fugl-Meyer assessment upper extremity, wolf motor function test, motor activity log, elbow extensor muscle strength, and modified Barthel index (p < 0.05). Post-intervention, the experimental group exhibited greater changes in the Fugl-Meyer assessment upper extremity, motor activity log, and elbow extensor muscle strength (p < 0.05).ConclusionOur study suggests that robot-assisted therapy in combination with trunk restraint is more effective for improving upper extremity function than only robot-assisted therapy in acute stroke patients.     

等速测试同步电刺激正常人上肢肌肉力量的分析

背景：力量训练方法多种多样,而运用负荷加上同步电刺激进行训练的方法在国内报道较少。 目的：通过选定有效增强肌力的电流参数,利用等速测试来观察同步电刺激对正常人上肢肌肉肌力的影响,探讨在传统力量训练的同时使用电刺激,对增强肌肉力量和对肌肉屈伸比的作用。 设计、时间及地点：随机分组,对照观察实验,2007-09/2008-01在江苏省机关医院康复医学实验室进行测试。 对象：南京体育学院16名在校大学生进行同步电刺激上肢肌肉力量训练。 方法：将16名参试者随机均分为2组：对照组和刺激组。对照组用哑铃进行传统力量训练;刺激组用哑铃与同步电刺激进行结合训练。哑铃负重进行屈伸力量训练肱二头肌、肱三头肌,共12周,3次/周,2组/次,每组同一质量连续举6次。刺激组在进行哑铃训练的同时将电极片分别置于肱二头肌肱三头肌起止点处,进行电刺激,刺激强度20 mA,波宽0.3 ms,每刺激6~10 s后休息30~50 s,实际共刺激100 s左右。 主要观察指标：训练12周后利用BIODEX多关节等速测力及康复系统测试参试者屈伸状态下2个不同速度：60 (°)/s和120 (°)/s的峰值力矩、平均功率、屈伸肌比值。 结果：①在60 (°)/s和120 (°)/s角速度下等速运动,实验组与对照组伸肌肌群力量增长并不明显,甚至出现了最大力量的下降。②在60 (°)/s和120 (°)/s下,刺激组和对照组平均肌肉作用能量如同最大力矩呈现的相类似的特点,即伸肌肌群增长不明显,屈肌肌群有明显增长。在60(°)/s下刺激组的平均肌肉作用能量增长55%,120 (°)/s下增长了29% ,相应对照组分别增长了16%。③在60 (°)/s下,即慢速运动下,刺激后屈伸比趋向目标值,而在120 (°)/s下,屈伸比均超过了目标值。 结论：①同步肌肉电刺激可有有效增强肌肉最大力量,但随着运动角速度的增大,增强的效果越发不明显。②同步肌肉电刺激可以有效增加肌肉做功效率,在不同角速度下均有较明显的提高。③同步肌肉电刺激可以使肌肉屈伸比趋向目标值,一定角速度下维持屈伸肌力平衡,但在快速运动时,由于屈肌肌力过度发展会引起屈伸肌比值偏离目标值,从而更易于引起肌肉损伤。     

Grip and Knee extension muscle strength reflect a common construct among adults

Introduction: Both grip and knee extension strength are often used to characterize overall limb muscle strength. We sought to determine if the measures actually reflect a common construct. Methods: The isometric grip and knee extension strength of 164 healthy men and women (range, 18–85 years) were measured bilaterally using standard procedures. Pearson correlations (r), Cronbach alpha, principal components analysis, and multiple regression/correlation were used to investigate the dimensionality of the measures. Results: Left and right grip forces and knee extension torques were highly correlated, internally consistent, and loaded on a single component. Gender and age explained the variance in both measures, but height added to the explanation of grip strength, whereas weight added to the explanation of knee extension strength. Conclusions: Among healthy adults, grip and knee extension strength reflect a common underlying construct. The measures, however, are affected differently by height and weight. Muscle Nerve 46: 555–558, 2012     

Caffeine improves neuromuscular function during maximal dynamic exercise

Introduction: In this study we tested the hypothesis that caffeine supplementation improves neuromuscular function, which has both nutritional and clinical relevance. Methods: Fourteen male subjects (mean ± SD: 23.8 ± 2.8 years) volunteered in a double‐blind, repeated‐measures study with placebo (PLA) or caffeine (CAFF) (6 mg kg^?1). Maximal voluntary isometric contractions (MVCs), evoked maximal twitch, and maximal isokinetic contractions during elbow flexion were assessed. Mechanical and electromyographic (EMG) signals from the biceps brachii muscle were recorded, and muscle fiber conduction velocity (CV) was calculated to evaluate changes in the muscle force–velocity relationship and muscle fiber recruitment. Results: The torque–angular velocity curve was enhanced after CAFF supplementation. This was supported by a concomitant increase of CV values (8.7% higher in CAFF). Conclusions: Caffeine improves muscle performance during short‐duration maximal dynamic contractions. The concomitant improvement of mean fiber CV supports the hypothesis of an effect of caffeine on motor unit recruitment. Muscle Nerve, 2011.