NEUROMUSCULAR DIFEERENCES BETWEEN ISOKINETIC AND SPORT MOVEMENTS: IMPLICATIONS FOR TRAINING - PERFORMANCE PREDICTION

INTRODUCTION. The relationship between isokinetic tests of muscle function and performance in sporting activities is not clear. Some studies reported significant correlations between isokinetics and performance in swimming, cycling, skiing and other activities (Bosco, 1983), whereas others reported weak or non existing relationships in swimming, jumping, cycling and kicking (Mognoni, 1994). One of the main reasons for these contradictory findings is, according to our opinion, the failure of such studies to consider in detail the differences in the mechanical function of the neuromuscular system during the different activities. The purpose of this study, therefore, was to examine differences in muscle length and velocity between isokinetic tests and sport/functional activities. METHODS. Kinematic data from an isokinetic knee extension test, a running and a wallcing motion and a simulated kicking action were used to drive a detailed musculoskeletal model of the lower limbs using the Software for Interactive Musculoskeletal Modelling (Delp, 1995) on a Silicon Graphics workstation. This system enables the accurate estimation of musculotendinous unit length and velocity changes during the simulated activities. RESULTS. The length of the rectus femoris and patella tendon unit as well as the length of the semimembranosus during the different activities are shown in Figure 1. Figure 1. Rectus Femoris and Semimembranosus length during isokinetic dynamometry and different sport/ functional activities. It is evident from these data that there are considerable differences in the length and velocity of contraction in two of the most important and dominant knee extensor and flexor muscles. CONCLUSIONS These results indicate that there are significant neuromuscular mechanics differences between common sporting-functional activities and isokinetic exercise, indicating that such isolated joint-controlled velocity tests should not be used for specific training or performance prediction in the above activities. REFERENCES Bosco C. et al. (1983). Eur. J. App. Phys., 51 (3), 357-364. Mognoni P. et al. (1994). J. Sport. Med. Phys. Fitness, 34(4), 357-361. Delp S. and Loan P. (1995). Comput. Biol. Med., 25(1), 21-34

Commentary on child-adult differences in muscle activation - A review

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The Effect of Isokinetic Training on Maximum Torque Output of Swimmers, Using the Akron Isokinetic Dynamometer

The important aspect of isokinetic exercise is that it allows the muscles to move at a constant predetermined angular velocity. This mode of exercise is based upon electromechanical devices with feedback systems which maintain the preset angular velocity of the limbs around the joint to be tested. The importance of isokinetic strength training for swimming performance is well supported by a number of studies (3, 7, 13). The purpose of this study was to determine if isokinetic training using a new isokinetic dynamometer, (AKRON, Ipswich, England), would increase the isokinetic strength of swimmers

ISOKINETIC PEAK POWER AND PREDICTION OF PERFORMANCE

The purpose of the present study was to examine the relationship between joint peak power during isokinetic concentric knee extension and during squat vertical jump performed on a Kistler force plate. Kjnematic data from both tests were colleded. Peak power was measured as the product of angular velocity and moment at the knee joint in both tests. Rank order correlations revealed that there is no relationship between the two tests concerning the peak power output at the knee joint. It was concluded that isolated joint isokinetic tests cannot be used to predict functional performance because of the differences in muscle and joint fundion characteristics during the different movements

Interplay between body stabilisation and quadriceps muscle activation capacity.

The study aimed to distinguish the effect of stabilisation and muscle activation on quadriceps maximal isometric voluntary contraction (MVC) torque generation. Nine subjects performed (a) an MVC with restrained leg and pelvis (Typical MVC), (b) a Typical MVC with handgrip (Handgrip MVC), (c) an MVC focusing on contracting the knee extensors only (Isolated knee extension MVC), and (d) an MVC with unrestrained leg and pelvis (Unrestrained MVC). Torque and activation capacity between conditions were compared with repeated measures ANOVA and dependent t-tests. EMG (from eleven remote muscles) was compared using Friedman's and Wilcoxon. Typical MVC (277.2±49.6Nm) and Handgrip MVC (261.0±55.4Nm) were higher than Isolated knee extension MVC (210.2±48.3Nm, p<0.05) and Unrestrained MVC (195.2±49.7Nm, p<0.05) torque. Typical MVC (83.1±15.9%) activation was higher than Isolated knee extension MVC (68.9±24.3%, p<0.05), and both Typical MVC and Handgrip MVC (81.8±17.4%) were higher than Unrestrained MVC (64.9±16.2%, p<0.05). Only flexor carpi radialis, biceps brachii, triceps brachii and external oblique muscles showed EMG differences, with Isolated knee extension MVC consistently lower than Typical MVC or Handgrip MVC. Stabilisation of the involved segments is the prime concern allowing fuller activation of the muscle, reinforcing the need for close attention to stabilisation during dynamometry-based knee joint functional assessment

Attainment of quiet standing in humans: Are the lower limb joints controlled relative to a misaligned postural reference?

In human quiet standing, the relative position between ankle joint centre and line of gravity is neurally regulated within tight limits. The regulation of the knee and hip configuration is unclear and thought to be controlled passively. However, perturbed standing experiments have shown a lower limb multi-joint coordination. Here, measuring the relative alignment between lower limb joints and the line of gravity in quiet standing after walking, we investigated whether the configuration is maintained over time through passive mechanisms or active control. Thirteen healthy adults walked without following a path and then stood quietly for 7.6 s on a force platform (up to four trials). The transition between initiation and steady-state standing (7.6 s) was measured using motion capture. Sagittal lower limb joint centres' position relative to line of gravity (CoGAP) and their time constants were calculated in each trial. Ankle, knee, and hip joint moments were also calculated through inverse dynamics. After walking, the body decelerated (t = 0.16 s). The ankle and hip joints' position relative to CoGAP measured at two time intervals of quiet standing (Mid = 0.5-0.55 s; End = 7.55-7.6 s) were different (mean ± SEM, CoGAP-Ankle_Mid = 47 ± 4 mm, CoGAP-Ankle_End = 58 ± 5 mm; CoGAP-Hip_Mid = 2 ± 5 mm, CoGAP-Hip_End = -5 ± 5 mm). The ankle, knee, and hip flexion-extension moments significantly changed. Changes in joints position relative to CoGAP and misalignment suggest that joint position is not maintained over 7.6 s, but regulated relative to a standing reference. Higher joint moments at steady-state standing suggest mechanisms other than passive knee and hip regulation are involved in standing. © 2007 - 2019 Frontiers Media S.A. All Rights Reserved

Influence of stair descent strategies and step height on centre of mass and gait kinetics in the elderly

Age-associated alterations in balance mechanisms and deteriorations in muscle strength may necessitate alternate stair descent strategies to ensure safe negotiation. The aim of the study was to compare the influence of increased step height and stair negotiation strategies; step-over-step (SoS) and step-by-step (SbS) on gait patterns in the elderly. Eleven elderly participants descended a four step custom built instrumented staircase at a self-selected speed. Participants descended using a SoS or SbS strategy on two step configurations: a rise height of 170mm (STD) and a rise height of 255mm (INC). A 3D motion analysis system synchronised with force platforms embedded into the staircase, was used to capture whole body centre of mass (CoM) velocity, acceleration and kinetic data of the leading limb.Compared to STDSoS, STDSbS resulted in reduced CoM vertical (-0.48m/s vs -0.09m/s) and A/P velocity (0.50m/s vs 0.21m/s) during late stance and swing transition with similar reductions in vertical and A/P velocity in INCSoS vs INCSbS (-0.67m/s vs -0.11m/s and 0.49m/s vs 0.23m/s). INCSoS resulted in increased plantarflexor (1.10Nm/kg vs 1.45Nm/kg) and hip extensor moment (-0.08Nm/kg vs 0.43Nm/kg) compared to STDSoS with no differences seen in SbS strategy. An alternate stair descent strategy offers greater CoM control in the potentially dangerous transition between stance and swing. Concurrently, the tandem double stance period negates the need for increased muscle moments in late stance required to eccentrically control the falling body mass in the traditional SoS strategy. SbS could offer increased CoM control and stability during stair descent

Effects of an acute bout of dynamic stretching on biomechanical properties of the gastrocnemius muscle determined by shear wave elastography

Aims The aim of this study was to examine the acute effects of dynamic stretching (DS) exercise on passive ankle range of motion (RoM), resting localized muscle stiffness, as measured by shear wave speed (SWS) of medial gastrocnemius muscle, fascicle strain, and thickness. Methods/Results Twenty-three participants performed a DS protocol. Before and after stretching, SWS was measured in the belly of the resting medial gastrocnemius muscle (MGM) using shear wave elastography. DS produced small improvements in maximum dorsiflexion (+1.5 ±1.5; mean difference ±90% confidence limits) and maximum plantarflexion (+2.3 ±1.8), a small decrease in fascicle strain (-2.6% ±4.4) and a small increase in SWS at neutral resting angle (+11.4% ±1.5). There was also a small increase in muscle thickness (+4.1mm ±2.0). Conclusions Through the use of elastography, this is the first study to suggest that DS increases muscle stiffness, decreases fascicle strain and increases muscle thickness as a result of improved RoM. These results can be beneficial to coaches, exercise and clinical scientists when choosing DS as a muscle conditioning or rehabilitation intervention

Influence of dynamic stretching on ankle joint stiffness, vertical stiffness and running economy during treadmill running

Data availability statement: The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.Copyright © 2022 Pamboris, Noorkoiv, Baltzopoulos, Powell, Howes and Mohagheghi. The purpose of the present study was to investigate whether and how dynamic stretching of the plantarflexors may influence running economy. A crossover design with a minimum of 48 h between experimental (dynamic stretching) and control conditions was used. Twelve recreational runners performed a step-wise incremental protocol to the limit of tolerance on a motorised instrumented treadmill. The initial speed was 2.3 m/s, followed by increments of 0.2 m/s every 3 min. Dynamic joint stiffness, vertical stiffness and running kinematics during the initial stage of the protocol were calculated. Running economy was evaluated using online gas-analysis. For each participant, the minimum number of stages completed before peak O2 uptake (V̇O2peak) common to the two testing conditions was used to calculate the gradient of a linear regression line between V̇O2 (y-axis) and speed (x-axis). The number of stages, which ranged between 4 and 8, was used to construct individual subject regression equations. Non-clinical forms of magnitude-based decision method were used to assess outcomes. The dynamic stretching protocol resulted in a possible decrease in dynamic ankle joint stiffness (−10.7%; 90% confidence limits ±16.1%), a possible decrease in vertical stiffness (−2.3%, ±4.3%), a possibly beneficial effect on running economy (−4.0%, ±8.3%), and very likely decrease in gastrocnemius medialis muscle activation (−27.1%, ±39.2%). The results indicate that dynamic stretching improves running economy, possibly via decreases in dynamic joint and vertical stiffness and muscle activation. Together, these results imply that dynamic stretching should be recommended as part of the warm-up for running training in recreational athletes examined in this study

The division of visual attention affects the transition point from level walking to stair descent in healthy, active older adults

Background: Stair descent is a frequent daily activity that poses great risks for injury due to falling. Very little is understood about the attentional demands of stair descent and their changes with aging. The present study compared combined locomotor and cognitive functioning during different phases of stair descent between healthy young and older individuals. Methods: Sixteen young and sixteen healthy older subjects walked down a 5-step staircase, performing a simultaneous visual Stroop task (i.e., a dual task) during the approach, transition or steady-state descent phases in some trials. Three dimensional kinematics of trunk and foot motion were recorded along with the accuracy and dual task costs (DTCs) for responses to the Stroop stimuli. Results: Dual tasking influenced both gait and cognitive performance for all subjects, and older adults generally walked slower with higher foot clearances and had greater DTCs. Specific age differences were found at stair transition where older adults showed more attentional effects. Conclusions: Healthy, active older adults showed changes to attention and planning due to normal aging specifically associated with a crucial point of fall risk during stair descent