Variability of concentric angle-specific isokinetic torque and impulse assessments of the knee extensors

Kinetic and kinematic profile of eccentric quasi-isometric loading

Eccentric quasi-isometric (EQI) contractions (maintaining a yielding contraction for as long as possible, beyond task failure) have gained interest in research and applied settings. However, little is known regarding the biomechanical profile of EQIs. Fourteen well-trained males performed four maximal effort knee-extensor EQIs, separated by 180 seconds. Angular impulse, velocity, and time-under-tension through the 30-100º range of motion (ROM), and in eight ROM brackets were quantified. Statistical parametric mapping, analyses of variance, and standardised effects (Hedges' g (ES), %Δ) detected between-contraction joint-angle-specific differences in time-normalised and absolute variables. Mean velocity was 1.34º·s-1 with most (62.5 ± 4.9%) of the angular impulse imparted between 40-70º. Most between-contraction changes occurred between 30-50º (p≤ 0.067, ES = 0.53 ± 0.31, 60 ± 52%), while measures remained constant between 50-100º (= 0.069-0.83, ES = 0.10 ± 0.26, 14.3 ± 24.6%). EQIs are a time-efficient means to impart high cumulative mechanical tension, especially at short to medium muscle lengths. However, angular impulse distribution shifts towards medium to long muscle lengths with repeat contractions. Practitioners may utilise EQIs to emphasize the initial portion of the ROM, and limit ROM, or apply EQIs in a fatigued state to emphasize longer muscle lengths.

The Validity of a Portable Strain-Gauge Apparatus Versus a Commercial Isokinetic Dynamometer for Evaluating Knee Extension Kinetics

Background

Isokinetic dynamometers are widely used when assessing neuromuscular function including knee extension kinetics. However, these dynamometers are often prohibitively expensive and are not portable. Thus strain-gauge technology has grown in popularity.

Purpose

The purpose of this study was to compare kinetic data captured via an isokinetic dynamometer against an affordable and portable strain-gauge with a treatment plinth during maximal isometric knee extensions.

Study Design

Cross-sectional study.

Methods

Healthy participants (8 males and 6 females; age 30.2±7.1 years) volunteered and performed knee extensions at a 90° knee angle on a dynamometer and a treatment plinth with a portable strain-gauge. Peak force (PF), peak rate of force development (PRFD), rate of force development (RFD2080) and impulse (IMP2080) from 20-80% of onset to peak force were assessed using both strain-gauge and isokinetic dynamometer. Between-device differences were evaluated by the Wilcoxon signed-rank test, Cohen's d effect sizes (ES), Pearson's correlation coefficients (r), and Bland-Altman plots.

Results

No significant or meaningful differences were identified between isokinetic and strain-gauge devices (all p≥0.268, ES≤0.35). However, slightly greater (2.5-9.5%) outputs were observed with the isokinetic dynamometer. Very large significant between-device correlations were found for PF (r=0.77, p=0.001) and PRFD (r=0.73, p=0.003), while small and moderate non-significant between-device correlations were found for RFD2080 (r=0.48, p=0.079) and IMP2080 (r=0.59, p=0.060). Bland-Altman plots did not reveal apparent biases from high to low performers.

Conclusions

These results indicate that the strain-gauge device can produce valid maximal and rapid force expression measurements. Similar results, such as those quantified via an isokinetic device, can be obtained without extreme rigour and constraint. The study's findings support using the practically relevant treatment plinth and strain-gauge combination as a suitable alternative to the isokinetic dynamometry for measuring PF and PRFD. Therefore, more rehabilitation and sports performance practitioners can confidently assess knee extension kinetics.

Level of Evidence

3.

The effects of regional quadriceps architecture on angle-specific rapid force expression

Evaluating anatomical contributions to performance can increase understanding of muscle mechanics and guide physical preparation. While the impact of anatomy on muscular performance is well studied, the effects of regional quadriceps architecture on rapid torque or force expression are less clear. Regional (proximal, middle, and distal) quadriceps (vastus lateralis, rectus femoris, and vastus intermedius) thickness (MT), pennation angle (PA), and fascicle length (FL) of 24 males (48 limbs) were assessed via ultrasonography. Participants performed maximal isometric knee extensions at 40°, 70°, and 100° of knee flexion to evaluate rate of force development from 0 to 200 ms (RFD0-200). Measurements were repeated on three occasions with the greatest RFD0-200 and mean muscle architecture measures used for analysis. Linear regression models predicting angle-specific RFD0-200 from regional anatomy provided adjusted correlations (√adjR2) with bootstrapped compatibility limits. Mid-rectus femoris MT (√adjR2 = 0.41-0.51) and proximal vastus lateralis FL (√adjR2 = 0.42-0.48) were the best single predictors of RFD0-200, and the only measures to reach precision with 99% compatibility limits. Small simple correlations were found across all regions and joint angles between RFD0-200 and vastus lateralis MT (√adjR2 = 0.28 ± 0.13; mean ± SD), vastus lateralis FL (√adjR2 = 0.33 ± 0.10), rectus femoris MT (√adjR2 = 0.38 ± 0.10), and lateral vastus intermedius MT (√adjR2 = 0.24 ± 0.10). Between-correlation comparisons are reported within the article. Researchers should measure mid-region rectus femoris MT and vastus lateralis FL to efficiently and robustly evaluate potential anatomical contributions to rapid knee extension force changes, with distal and proximal measurements providing little additional value. However, correlations were generally small to moderate, suggesting that neurological factors may be critical in rapid force expression.

Equations for estimating the static supportive torque provided by upper-limb exoskeletons

Upper-limb exoskeletons are gaining traction in industrial work environments. However, other than advertised general specifications (e.g., peak support angle), the support torque provided throughout the reach envelope is largely unknown to end users. As such, this paper describes a methodology for measuring the specific supportive torque provided by upper-limb exoskeletons. The support of four commercially available passive upper-limb exoskeletons was quantified using an isokinetic dynamometer for all support ranges and levels (n = 68). Tests were repeated four times to determine between-session reliability. Intraclass correlation coefficients demonstrated 'Good' to 'Excellent' reliability, except for one condition. Polynomial regression equations were developed for each condition to predict exoskeleton support for any upper-limb elevation angle between 10° and 180°. These equations can be used to approximate upper-limb exoskeleton support in digital human modeling assessments, or to aid selection of exoskeleton settings specific to a worker's anthropometry and work task location.

Multimodal physical training combined with tDCS improves physical fitness components in people after stroke: a double-blind randomized controlled trial

BACKGROUND

Transcranial direct current stimulation (tDCS) seems to be a potential tool to optimize the long-term effects of multimodal physical training (MPT) on fitness components in post-stroke patients.

OBJECTIVE

We investigated the effects of cortical tDCS combined with MPT on motor function reflected by strength, motor performance, and cardiorespiratory capacity in chronic stroke patients.

METHODS

This double-blind randomized controlled trial included 18 volunteers (55 ± 10 y, 72 ± 13 kg), who underwent MPT preceded by either sham stimulation (SHAM) or 2 mA bi-hemispheric tDCS. MPT consisted of 24 sessions of 60-70 min performed 2 d/wk within 12-16 weeks, with individualized intensity. Outcomes were Fugl-Meyer scores for lower limbs (FM-LL), and total (FM-Total); speed in the 10-m walk test (10MWT); oxygen uptake and work output at maximal effort (VO_2max and W_max), and gas exchange threshold (VO₂-GET and W-GET); peak torque of isokinetic knee extension (PT-EXT) and flexion (PT-FLEX) of paretic and non-paretic limbs; bilateral strength deficit during knee extension (DS-EXT) and flexion (DS-FLEX).

RESULTS

Pre- vs. post-intervention improvements were detected in tDCS vs. SHAM (p < 0.05) for FM-total (29.6% vs. 15.9%; effect size [ES] = 0.78), FM-LL (35.9% vs. 9.0%; ES = 1.23), 10MWT (10.6% vs. 3.8%; ES = 0.67), W_max (75.0% vs. 4.3%; ES = 1.68), W-GET (91.6% vs. 12.4%; ES = 1.62), PT-EXT (25.6% vs. -6.5%; ES = 1.94) and PT-FLEX (26.3% vs. 9.8%; ES = 0.65) of the paretic limb, and DS-EXT (-13.7% vs. 2.5; ES = 1.43).

CONCLUSION

Bi-hemispheric cortical tDCS optimized the effects of MPT performed with moderate volume and intensity upon muscle strength, motor function, and cardiorespiratory performance in stroke hemiparetic survivors. (Registration number RBR-22rh3p).

Intersession Variability of Knee Extension Kinetics Using a Strain Gauge Device With Differing Clinically Practical Physical Constraints

CONTEXT

Intrasession reliabilities of isometric knee extension kinetics via portable strain gauge have been reported across several knee joint angles and constraints. However, intersession variabilities, which are more valuable, have yet to be determined. Therefore, we aimed to quantify the intersession variability of knee extension kinetics over 3 testing sessions using an affordable and portable strain gauge.

DESIGN

Participants performed maximum voluntary isometric contractions of the knee extensors over 3 sessions.

METHODS

Eleven (6 men and 5 women; 31 [6.4] y) volunteers performed maximum voluntary isometric contractions in constrained (isokinetic setup with thigh and chest straps) and unconstrained (treatment plinth) conditions. Peak force (PF), peak rate of force development, rate of force development (RFD), and impulse (IMP) from 20% to 80% of PF were assessed. Means, SDs, percentage changes, minimal detectable changes, coefficients of variation (CV), and intraclass correlation coefficients (ICC) were calculated and reported.

RESULTS

PF had the lowest intersession variability regardless of condition (CV = 5.5%-13.8%, ICC = .67-.93). However, variability of peak rate of force development (CV [range] = 12.2%-24.7%, ICC = .50-.78), RFD (CV = 10.0%-26.8%, ICC = .48-.84), and IMP (CV = 15.2%-35.4%, ICC = .44-.88) was moderate at best. The constrained condition (CV [SD] = 14.1% [4.8%], ICC = .74 [.08]) had lower variability compared with the plinth (CV = 19.8% [7.9%], ICC = .68 [.15]). Variability improved from sessions 1 to 2 (CV = 20.4% [7.7%], ICC = .64 [.14]) and to sessions 2 to 3 (CV = 15.3% [6.4%], ICC = .76 [.10]).

CONCLUSIONS

PF can be assessed regardless of setup. However, RFD and IMP changes across sessions should be approached with caution. Backrests and thigh straps improve RFD and IMP variability, and at least 1 familiarization session should be provided before relying on knee-extensor kinetics while utilizing a portable strain gauge.

No association between dynamic trunk flexion strength and throwing velocity in elite women handball players

BACKGROUND: The relationship between strength and throwing velocity is much investigated in handball, but core strength is largely ignored. Only four studies have investigated the effect of core training on handball throwing velocity, reporting conflicting results in amateur players. However, lack of specificity and deficient technical execution of throwing in amateurs can obscure the results. OBJECTIVE: To examine the direct association between trunk flexion strength and throwing velocity in elite handball players, using women as a model. METHODS: Sixteen women players from an elite-level Norwegian handball team participated in the study. Strength in trunk flexion, shoulder extension, internal shoulder rotation, and forearm pronation was assessed using isokinetic dynamometer measurements (peak moment, total work, angular impulse). Throwing velocity in both the standing throw with run-up and the jump throw was determined from motion capture measurements. To account for arm strength, the association between trunk flexion strength and throwing velocity was examined using partial correlation analyses. RESULTS: No significant association was found between any measure of trunk flexion strength and throwing velocity for either throwing technique (explained variance ⩽ 13.7%). CONCLUSIONS: The results indicate that isolated, dynamic trunk flexion strength is not a differentiating factor for handball throwing velocity in elite women players.

The effect of regional quadriceps anatomical parameters on angle-specific isometric torque expression

The length–tension relationship affects knee extension performance; however, whether anatomical variations in different quadriceps regions affect this relationship is unknown. Regional (proximal, middle, distal) quadriceps thickness (MT), pennation angle, and fascicle length of 24 males (48 limbs) were assessed via ultrasonography. Participants also performed maximal voluntary isometric torque (MVIT) assessments at 40°, 70°, and 100° of knee flexion. Measures were recorded on 3 separate occasions. Linear regression models predicting angle-specific torque from regional anatomy provided adjusted simple and multiple correlations (√adjR2) with bootstrapped compatibility limits to assess magnitude. Middle vastus lateralis MT and MVIT at 100° (√adjR2 = 0.64) was the largest single correlation, with distal vastus lateralis MT having the greatest mean correlations regardless of angle (√adjR2 = 0.61 ± 0.05, mean ± SD). Lateral distal MT and architecture had larger (Δ√adjR2 = 0.01 to 0.43) single and multiple correlations with MVIT than the lateral proximal (√adjR2 = 0.15 to 0.69 vs −0.08 to 0.65). Conversely, middle anterior MT had greater (Δ√adjR2 = 0.08 to 0.38) single and multiple correlations than proximal MT (√adjR2 = 0.09 to 0.49 vs −0.21 to 0.14). The length–tension relationship was trivially affected by regional quadriceps architecture. The middle and distal quadriceps were the strongest predictors of MVIT at all joint angles. Therefore, researchers may wish to focus on middle and distal lateral quadriceps anatomy when performing ultrasonographic evaluations.

Novelty: The length–tension relationship is minimally affected by regional quadriceps anatomical parameters. Middle and distal vastus lateralis and lateral vastus intermedius anatomy were consistently the best predictors of torque. Practitioners may focus their assessments on the middle and distal regions of the lateral quadriceps’ musculature.

Association between Lysholm score and muscular torque deficit after anterior cruciate ligament reconstruction

PURPOSE

The asymmetry of muscular strength after anterior cruciate ligament reconstruction (ACLR) is associated with increase in the development of new lesions. This asymmetry is precisely assessed by isokinetic dynamometry which is a high-cost technique, limited to major centers and hospitals. Thus, the aim of this study was to test the accuracy of one of the most frequently used functional questionnaires, the Lysholm score, to diagnose the knee torque deficit.

METHODS

In total, 115 patients were evaluated after ACLR. Knee symptoms were evaluated using the Lysholm questionnaire and knee extensor and flexor peak torque during maximal isokinetic concentric contractions at 60° s^-1 (5 repetitions) and 180° s^-1 (15 repetitions). Patients with <20% peak torque deficit were considered symmetric (normal).

RESULTS

An increase in the Lysholm score was associated with a deficit reduction in the peak torque of knee extensors at 60° s^-1 (r = -0.294) and 180° s^-1 (r = -0.297) (p < 0.05 for both). Cutoff Lysholm scores of >90 points for 60° s^-1 allowed the correct diagnosis of symmetry in 71% and of >89 points for 180º·s^-1 allowed the correct diagnosis of symmetry in 73%, for knee extensors. Patients with a Lysholm score of >89 points presented an isokinetic deficit 36% lower than patients with a Lysholm score of ≤89 points (p < 0.05).

CONCLUSION

A Lysholm score of >89 points has predictive value for deficits in the peak torque of knee extension (<20%). However, replacement of the isokinetic evaluation by this instrument must be performed with caution because of its accuracy.

Concurrent Validity and Reliability of Three Ultra-Portable Vertical Jump Assessment Technologies

Vertical jump is a valuable training, testing, and readiness monitoring tool used across a multitude of sport settings. However, accurate field analysis has not always been readily available or affordable. For this study, two-dimensional motion capture (Mo-Cap), G-Flight micro-sensor, and PUSH accelerometer technologies were compared to a research-grade force-plate. Twelve healthy university students (7 males, 5 females) volunteered for this study. Each participant performed squat jumps, countermovement jumps, and drop jumps on three separate occasions. Between-device differences were determined using a one-way repeated measures ANOVA. Systematic bias was determined by limits of agreement using Bland-Altman analysis. Variability was examined via the coefficient of variation, interclass correlation coefficient, and typical error of measure. Dependent variables included jump height, contact-time, and reactive strength index (RSI). Mo-Cap held the greatest statistical similarity to force-plates, only overestimating contact-time (+12 ms). G-Flight (+1.3-4 cm) and PUSH (+4.1-4.5 cm) consistently overestimate jump height, while PUSH underestimates contact-time (-24 ms). Correspondingly, RSI was the most valid metric across all technologies. All technologies held small to moderate variably; however, variability was greatest with the G-Flight. While all technologies are practically implementable, practitioners may want to consider budget, athlete characteristics, exercise demands, set-up, and processing time before purchasing the most appropriate equipment.

Short-term neuromuscular, morphological, and architectural responses to eccentric quasi-isometric muscle actions

PURPOSE

Eccentric quasi-isometric (EQI) contractions have been proposed as a novel training method for safely exposing the musculotendinous system to a large mechanical load/impulse, with few repetitions. However, understanding of this contraction type is rudimentary. We aimed to compare the acute effects of a single session of isotonic EQIs with isokinetic eccentric (ECC) contractions.

METHODS

Fifteen well-trained men performed a session of impulse-equated EQI and ECC knee extensions, with each limb randomly allocated to one contraction type. Immediately PRE, POST, 24/48/72 h, and 7 days post-exercise, regional soreness, quadriceps swelling, architecture, and echo intensity were evaluated. Peak concentric and isometric torque, rate of torque development (RTD), and angle-specific impulse were evaluated at each time point.

RESULTS

There were substantial differences in the number of contractions (ECC: 100.8 ± 54; EQI: 3.85 ± 1.1) and peak torque (mean: ECC: 215 ± 54 Nm; EQI: 179 ± 28.5 Nm). Both conditions elicited similar responses in 21/53 evaluated variables. EQIs resulted in greater vastus intermedius swelling (7.1-8.8%, ES = 0.20-0.29), whereas ECC resulted in greater soreness at the distal and middle vastus lateralis and distal rectus femoris (16.5-30.4%, ES = 0.32-0.54) and larger echogenicity increases at the distal rectus femoris and lateral vastus intermedius (11.9-15.1%, ES = 0.26--0.54). Furthermore, ECC led to larger reductions in concentric (8.3-19.7%, ES = 0.45-0.62) and isometric (6.3-32.3%, ES = 0.18-0.70) torque and RTD at medium-long muscle lengths.

CONCLUSION

A single session of EQIs resulted in less soreness and smaller reductions in peak torque and RTD versus impulse-equated ECC contractions, yet morphological shifts were largely similar. Long-term morphological, architectural, and neuromuscular adaptations to EQI training requires investigation.

Variability of regional quadriceps echo intensity in active young men with and without subcutaneous fat correction

Quantifying echo intensity (EI), a proposed measure of muscle quality, is becoming increasingly popular. Additionally, much attention has been paid to regional differences in other ultrasonically evaluated measures of muscle morphology and architecture. However, the variability of regional (proximal, middle, distal) EI of the vastus lateralis, rectus femoris, and lateral and anterior vastus intermedius has yet to be determined. Twenty participants (40 limbs), were evaluated on 3 occasions, separated by 7 days. Intersession variability of EI with and without subcutaneous fat correction was quantified. Furthermore, the interchangeability of corrected EI across regions was evaluated. Variability of regional quadriceps EI was substantially lower with subcutaneous fat correction (intraclass correlation coefficient (ICC) = 0.81-0.98, coefficient of variation (CV) = 4.5%-16.8%, typical error of measure (TEM) = 0.13-0.49) versus raw values (ICC = 0.69-0.98, CV = 7.7%-42.7%, TEM = 0.14-0.68), especially when examining the vastus intermedius (ICC = 0.81-0.95, CV = 7.1%-16.8%, TEM = 0.23-0.49 vs. ICC = 0.69-0.92, CV = 22.9%-42.7%, TEM = 0.31-0.68). With the exception of the rectus femoris and vastus intermedius (p ≥ 0.143, effect size (ES) ≤ 0.18), corrected EI was greater for proximal and distal regions when compared with the midpoint (p ≤ 0.038, ES = 0.38-0.82). Researchers and practitioners should utilize subcutaneous fat thickness correction to confidently evaluate EI at all regions of the quadriceps. Regional EI cannot be used interchangeably for the vastus muscles, likely because of an increase in fibrous content towards the myotendinous junctions. Novelty Regional quadriceps echo intensity was reliable with and without correction for subcutaneous fat thickness. Intersession variability of regional quadriceps echo intensity was substantially improved following subcutaneous fat correction. Quadriceps echo intensity increased towards myotendinous junctions in the vastus muscles.