Decreased rate of leg extensor force development in independently ambulant patients with acute stroke with mild paresis

We aimed to examine the rate of force development (RFD) of knee extensors on both sides in independently ambulant patients with acute stroke with mild paresis compared with that in age-matched healthy adults. A total 31 patients with acute stroke history (patient group: 67 ± 12 years) and 54 age-matched healthy, community-dwelling adults (control group: 67 ± 8 years) were included. Maximum voluntary contraction (MVC) and RFD were assessed <1 month post-stroke during isometric knee extension (sitting position; 90° knee flexion) using a hand-held dynamometer. RFD was measured as the average slope of the torque–time curve over time intervals of 0–50 ms and 0–200 ms from contraction onset. In the patient group, MVC and RFD for 0–50 ms were significantly lower on the affected side than on the unaffected side (p < 0.01). RFD was significantly decreased in the patient group, to 32%–38% and 62%–71% of that in the control group, over 0–50 ms and 0–200 ms, respectively, regardless of the affected side (p < 0.01). No significant differences in MVC between patient and control groups were observed for either side. RFD of the knee extensors significantly decreased without MVC reduction in patients with acute stroke history compared with that in age-matched healthy adults in both the affected and unaffected sides. These results suggest that decrease in RFD was initiated from the acute phase of stroke, even in patients with stroke who had good motor function.     

Generality versus specificity: a comparison of dynamic and isometric measures of strength and speed-strength

Considerable debate exists as to whether the qualities of muscle function exist as general or specific physiological capacities. If there is a generality of muscle function then strong relationships would exist between various measures of function for the same muscle(s), independent of the test contraction, mode or velocity. The purpose of this study was to examine the relationship between isometric and dynamic measures of muscle function to determine the existence of generality or specificity. A group of 22 men, experienced in weight training, were tested for lower and upper body dynamic and isometric measures of strength and speed-strength. The changes in these measures consequent to a resistance training programme were also investigated. The results of this study indicated that whilst isometric and dynamic measures of strength did significantly correlate (r=0.57-0.61), the relationship was below that required to denote statistical generality. More important, the changes in isometric and dynamic strength consequent to a dynamic heavy resistance training programme were unrelated (r=0.12-0.15). Thus the mechanisms that contribute to enhanced dynamic strength appearred unrelated to the mechanisms that contribute to enhanced isometric strength. Measures of dynamic and isometric speed-strength were unrelated, as were the changes in these measures resulting from training. The results of this study demonstrated that a generality of muscle function did not exist and that modality specific results were observed. Consequently this study calls into question the validity of isometric tests to monitor dynamically induced training adaptations.     

Assessment of ankle plantar flexor neuromuscular properties: A reliability study

This study aimed to determine test–retest reliability of ankle plantar flexor neuromuscular properties in healthy people to improve understanding of additional measurement and analysis procedures that may be used in outcome assessment. Ten healthy participants (age 29.60 ± 5.36 years) volunteered. Isometric torque_max, rate of torque development (RTD), rate of electromyography rise (RER), impulse, electromechanical delay (EMD), torque steadiness, and torque sensing were obtained during two testing sessions 60 min apart. ICC values ranged from 0.81 to 0.99, indicating good to excellent test–retest reliability. Lower bands of the 95% CIs were all above 0.75 apart from the early phase measures (≤50 ms) derived from explosive torque-time and EMG-time curves, which were between 0.32 and 0.73, indicating poor to moderate reliability. Heteroscedasticity was observed for RTD, impulse, and EMD. LOA as a function of the mean (X̅) for these measures ranged from mean_difference ± 0.25X̅ to ± 0.68X̅. EMD showed excellent reliability (ICC = 0.90; 95% CI [0.63, 0.98]). Torque sensing and torque steadiness showed good reliability (0.81 ≤ ICC ≤ 0.89). Thus, ankle plantar flexor neuromuscular properties showed good to excellent test–retest reliability. However, reliability of measures in the early phase of muscle contraction were consistently lower than the late phase.     

Modulation of the rate of force development in hip abductor muscles by neuromuscular electrical stimulation during gait

Abstract

Purpose/aim of the study: An increase of hip abductor muscle strength contributes to the increase in gait speed. It is known that the rate of force development (RFD), an indicator of muscle strength, is increased by the combined use of low-intensity neuromuscular electrical stimulation (NMES) to the glutaeus medius (GM) and low-load resistance training (RT). However, it is unclear whether low-intensity neuromuscular electrical stimulation of the glutaeus medius during walking also increases the rate of force development. The aim of this study was to clarify whether NMES to the GM during gait modulates the RFD of the hip abductor muscles in healthy adults.

Materials and methods: Twenty-two healthy adults randomly received both gait with sub-motor threshold NMES and gait with sham NMES conditions. The RFD was assessed at pre- and post-intervention. A two-way repeated measures analysis of variance was used to analyse the effects of time and intervention.

Results: Gait with sub-motor threshold NMES condition significantly increased the RFD in shorter time interval (0–50 and 0–100?ms) compared to gait with sham NMES condition.

Conclusions: These findings suggest that the adding low-intensity NMES of the GM to gait is effective in increasing the RFD of the hip abductor muscles.     

Validity and reliability of isometric,isokinetic and isoinertial modalities for the assessment of quadriceps muscle strength in patients with total knee arthroplasty

Reliability of isometric, isokinetic and isoinertial modalities for quadriceps strength evaluation, and the relation between quadriceps strength and physical function was investigated in 29 total knee arthroplasty (TKA) patients, with an average age of 63 years. Isometric maximal voluntary contraction torque, isokinetic peak torque, and isoinertial one-repetition maximum load of the involved and uninvolved quadriceps were evaluated as well as objective (walking parameters) and subjective physical function (WOMAC). Reliability was good and comparable for the isometric, isokinetic, and isoinertial strength outcomes on both sides (intraclass correlation coefficient range: 0.947–0.966; standard error of measurement range: 5.1–9.3%). Involved quadriceps strength was significantly correlated to walking speed (r range: 0.641–0.710), step length (r range: 0.685–0.820) and WOMAC function (r range: 0.575–0.663), independent from the modality (P < 0.05). Uninvolved quadriceps strength was also significantly correlated to walking speed (r range: 0.413–0.539), step length (r range: 0.514–0.608) and WOMAC function (r range: 0.374–0.554) (P < 0.05), except for WOMAC function/isokinetic peak torque (P > 0.05). In conclusion, isometric, isokinetic, and isoinertial modalities ensure valid and reliable assessment of quadriceps muscle strength in TKA patients.     

Cross training effects of non-paralytic dorsiflexion muscle strengthening exercise on paralytic dorsiflexor muscle activity,gait ability,and balancing ability in patients with chronic stroke: A randomized,controlled, pilot trial

Objective:To investigate the effects of non-paralytic dorsiflexion muscle strengthening exercise on functional abilities in chronic hemiplegic patients after stroke.Methods:A total of 21 patients with chronic stroke underwent dorsiflexion muscle strengthening exercise (MST) 5 times a week for 6 weeks (the experimental group, MST to non-paralytic dorsiflexion muscles, n=11; the control group, MST to paralytic dorsiflexion muscles; n=10). Paralytic dorsiflexor muscle activities (DFA) and 10 m walking tests (10MWT) and timed up and go tests (TUG) were measured before and after intervention.Results:A significant increase in DFA was observed after intervention in the experimental and control groups (p<0.05) (experimental 886.6% for reference voluntary contraction (RVC), control 931.6% for RVC). TUG and 10MWT results showed significant reductions post-intervention in the experimental and control groups (experimental group -5.6 sec, control -4.8 sec; experimental group -3.1 sec, control, -3.9 sec; respectively). No significant intergroup difference was observed between changes in DFA or between changes in TUG and 10MWT results after intervention (p>.05).Conclusion:Strengthening exercise performed on non-paralytic dorsiflexion muscles had positive cross-training effects on paralytic dorsiflexor muscle activities, balance abilities, and walking abilities in patients with chronic stroke.     

Early vs. late rate of torque development: Relation with maximal strength and influencing factors

We re-examined the relationship between rate of torque development (RTD) and maximal voluntary contractions (MVC) torque, and investigated some possible neuromuscular determinants of early (≤100 ms) and late (≥200 ms) RTD. Seventeen healthy men performed maximal explosive isometric knee extensions at five joint angles, from which MVC torque, RTD at different time intervals (50–250 ms), and early quadriceps EMG activity (EMG₅₀) were evaluated. Quadriceps muscle thickness (MT) was quantified by longitudinal ultrasonography. The relationship between MVC torque, EMG₅₀ and MT against RTD was assessed with Pearson’s and repeated measures correlation coefficients. Moderate-to-strong correlation coefficients were observed between MVC torque and RTD (r = 0.50–0.88, p < 0.001), with stronger relationships for late RTD than for early RTD. Weak-to-strong correlation coefficients were observed amongst RTD and EMG₅₀ (r = 0.37–0.83, p < 0.001), with stronger relationships for early RTD than for late RTD. Only late RTD was significantly correlated with MT, though only moderately (r = 0.50–0.52, p < 0.05). These findings suggest that early and late knee extension RTD are potentially governed by different neuromuscular factors. Neuromuscular activation seems to have a greater influence on early RTD than on late RTD, and vice versa for muscle mass.     

Faster intrinsic rate of torque development in elbow flexors than knee extensors: Effect of muscle architecture?

We studied the effect of pennate vs. fusiform muscle architecture on the rate of torque development (RTD) by examining the predominately fusiform elbow flexors (EF) and highly-pennate knee extensors (KE). Seventeen male volunteers (28.4 ± 6.2 years) performed explosive isometric EF and KE contractions (MVCs). Biceps brachii and vastus lateralis fascicle angles were measured to confirm their architecture, and both the rate of voluntary muscle activation (root-mean-square EMG in the 50 ms before contraction onset; EMG_-50) and electromechanical delay (EMD; depicting muscle-tendon series elasticity) were assessed as control variables to account for their influence on RTD. MVC torque, early (RTD₅₀) and late (RTD₂₀₀) RTDs were calculated and expressed as absolute and normalized values. Absolute MVC torque (+412%), RTD₅₀ (+215%), and RTD₂₀₀ (+427%) were significantly (p < 0.001) higher in KE than EF. However, EF RTD₅₀ was faster (+178%) than KE after normalization (p = 0.02). EMG_-50 and EMD did not differ between muscle groups. The results suggest that the faster absolute RTD in KE is largely associated with its higher maximal torque capacity, however in the absence of differences in rates of muscle activation, fiber type, and EMD the fusiform architecture of EF may be considered a factor allowing its faster early RTD relative to strength capacity.