Isometric Strength Training Research Articles

Early neural responses to strength training

The neural adaptations that accompany strength training have yet to be fully determined. Here we sought to address this topic by testing the idea that strength training might share similar mechanisms with some forms of motor learning. Since ballistic motor learning is accompanied by a shift in muscle twitches induced by transcranial magnetic stimulation (TMS) toward the training direction, we sought to investigate if these changes also occur after single isometric strength training sessions with various contraction duration and rate of force development characteristics (i.e., brief or sustained ballistic contractions or slow, sustained contractions). Twitch force resultant vectors and motor-evoked potentials (MEPs) induced by TMS were measured before and after single sessions of strength training involving the forearm muscles. Participants (n = 12) each performed three training protocols (each consisting of 4 sets of 10 repetitions) and served as their own control in a counterbalanced order. All three training protocols caused a significant (P < 0.05) shift in TMS-induced twitch force resultant vectors toward the training direction, followed by a gradual shift back toward the pretraining direction. The strongest effect was found when training involved both ballistic and sustained force components. There were no large or consistent changes in the direction of twitches evoked by motor nerve stimulation for any of the three training protocols. We suggest that these early neural responses to strength training, which share similar corticospinal changes to motor learning, might reflect an important process that precedes more long-term neural adaptation that ultimately enhance strength.

Corticospinal and motor unit adaptations to rapid isometric strength training

Corticospinal and motor unit adaptations to rapid isometric strength training

Corticospinal properties following short-term strength training of an intrinsic hand muscle

Practicing skilled tasks that involve the use of the hand and fingers has been shown to lead to adaptations within the central nervous system (CNS) underpinning improvements in the performance of the acquired task. However, neural adaptations following a period of strength training in the hand is not well understood. In order to determine the neural adaptations to strength training, we compared the effect of isometric strength training of the right first dorsal interosseous (FDI) muscle on the electromyographic (EMG) responses to transcranial magnetic stimulation (TMS) over left M1. The specific aim of the study was to investigate the corticospinal responses, including latency, motor-evoked potential amplitude (MEP), and silent period duration (SP) following 4 week of strength training of the FDI muscle. Sixteen healthy adults (13 male, three female; 24.12 ± 5.21 years), were randomly assigned into a strength training ( n = 8) or control group ( n = 8). Corticospinal measures of active motor threshold (AMT), MEP amplitude, and SP duration were obtained using TMS during 5% and 20% of maximal voluntary contraction force (MVC) pre and post 4 week strength training. Following training, MVC force increased by 33.8% ( p = .01) in the training group compared to a 13% increase ( p = .2) in the untrained group. There were no significant differences in AMT, latency, or MEP amplitude between groups following training. However, in the trained group, there was a 16 ms reduction in SP duration at 5% of MVC ( p = .01) and 25 ms reduction in SP duration at 20% of MVC ( p = .03). These results demonstrate a task dependent adaptation in corticospinal inhibition via a reduction in cortical SP duration that may in part underpin the strength increases observed following strength training.

Dynamic splinting for pronation contracture following a spinal cord injury

Background This report discusses the success of using multiple protocols/modalities to reduce forearm contracture in a 34-year-old, African American man who had suffered a spinal cord injury (SCI) over 2 years before this treatment. The patient's initial maximal active range of motion (AROM) in supination was −85° left and −60° right, and his initial passive range of motion (PROM) was +12° left and +50° right. Methods Intervention included occupational therapy five times per week and the protocols employed included manual AROM and PROM training, isometric strength training, handwriting, self-feeding and grooming training. Electrical stimulation for shoulder flexion and elbow extension, and a unique new modality, the Supination Dynasplint®, was also used for 45 min on each arm, twice daily. Results After three months, the patient regained over 40° AROM of supination in each arm. This benefitted the patient's ability to use utensils for eating, improved his handwriting skills and he regained the ability to use a urinal at night while in bed.

Neural adaptations underlying cross-education after unilateral strength training

The purpose of this study was to investigate the effects of 4-week (16 sessions) unilateral, maximal isometric strength training on contralateral neural adaptations. Subjects were randomised to a strength training group (TG, n = 15) or to a control group (CG, n = 11). Both legs of both groups were tested for plantar flexion maximum voluntary isometric contractions (MVCs), surface electromyogram (EMG), H-reflexes and V-waves in the soleus (SOL) and gastrocnemius medialis (GM) superimposed during MVC and normalised by the M-wave (EMG/M(SUP), H(SUP)/M(SUP), V/M(SUP), respectively), before and after the training period. For the untrained leg, the TG increased compared to the CG for MVC torque (33%, P < 0.01), SOL EMG/M(SUP) (32%, P < 0.05) and SOL V/M(SUP) (24%, P < 0.05). For the trained leg, the TG increased compared to the CG for MVC torque (40%, P < 0.01), EMG/M(SUP) (SOL: 38%, P < 0.05; GM: 60%, P < 0.05) and SOL V/M(SUP) (72%, P < 0.01). H(SUP)/M(SUP) remained unchanged for both limbs. No changes occurred in the CG. These results reinforce the concept that enhanced neural drive to the contralateral agonist muscles contributes to cross-education of strength.

O044 Changes in upper limb isometric strength and error tracking following training using functional electrical stimulation

CHANGES IN UPPER LIMB ISOMETRIC STRENGTH AND ERROR TRACKING FOLLOWING TRAINING USING ITERATIVE LEARNING CONTROL (ILC) MEDIATED BY FUNCTIONAL ELECTRICAL STIMULATION (FES) Authors: Hughes, A. M. MSc1, Freeman, C. PhD2, Burridge, J. PhD1, Chappell, P. PhD2, Lewin, P. PhD2 and Rogers, E. PhD2 Affiliations: University of Southampton, Southampton, SO17 1BJ, UK 1 School of Health Professions and Rehabilitation Sciences 2 School of Electronics and Computer Science SUMMARY Based on existing motor control theory, an intervention involving a robot, ILC and FES was developed and tested on five chronic stroke patients. Improvements were seen in isometric strength and error tracking. CONCLUSIONS ILC mediated by FES enabled five chronic stroke subjects to accurately track a range of trajectories. Over time this related to an improvement in motor control reflected by increasing accuracy observed in unassisted tracking, and in isometric strength. INTRODUCTION Current opinion in motor learning, reinforced by clinical evidence, supports the use of FES and robot therapy to improve motor control [1-3]. ILC is a technique applicable to processes which repeatedly perform a task with a view to sequentially improving accuracy such as trajectory following in robots. The aim of this study is to test the feasibility of applying ILC to neurological rehabilitation. PATIENTS/MATERIALS and METHODS 5 hemiplegic stroke subjects underwent screening tests, and baseline assessments including isometric strength. Subjects used a robotic workstation to track 2 dimensional trajectories, over 18 intervention sessions within a 3 month period. At the beginning and end of each intervention session the ability of the stroke subject to track four trajectories without any FES or robot assistance was assessed. During the treatment sessions, ILC was used to modulate the FES applied to their triceps muscles in terms of timing and amplitude to improve tracking performance, whilst encouraging a maximal voluntary contribution to the task. Assessments of isometric muscle strength in six directions from a mid position were repeated after the eighteen sessions and for two subjects after an additional seven sessions. RESULTS Improvements in isometric strength were seen for all individual subjects after the intervention, with significant improvements for five out of six directions. Unassisted performance of the tracking tasks improved significantly for 3 out of the 4 tasks across the group. Subjects who performed poorly on the initial visit, showed the biggest improvements in tracking. DISCUSSION Analysis of the variability of the results may assist in the identification of good responders. Future work with the existing system includes assessing the potential for use with other neurological conditions, such as cerebral palsy and incomplete spinal cord injury. A subsequent study will develop a system for reaching in three dimensions and include opening the wrist and hand using ‘Smart glove’ as a position sensor. REFERENCES [1] De Kroon, J. R., van der Lee, J. H., Izerman, M. J., & Lankhorst, G. J. 2002, Clinical Rehabilitation, vol. 16, pp. 350-360. [2] Schmidt, R. A. & Lee, T. D. Motor control and learning a behavioural emphasis. 3rd Edition. 261-285. 1999. Human Kinetics. [3] Kwakkel, G., Kollen, B. J., & Krebs H.I 2008, Neurorehabilitation and Neural Repair, vol. 22, pp. 111-121.

Effects of isometric strength training followed by no exercise and Humulus lupulus L–enriched diet on bone metabolism in old female rats

We investigated in female rats the effects on bone metabolism of a prolonged no-training period, subsequent to an isometric exercise program, performed during young adulthood and those of a long-term consumption of Humulus lupulus L–enriched diet (genistein 1.92 and daidzein 1.24 mg/kg diet) combined or not with isometric training. Forty-eight rats (4 weeks old) were randomly divided into 4 groups: trained (C-Tr) or nontrained rats (C-NTr) fed with control diet and trained (H-Tr) or nontrained rats (H-NTr) fed with Humulus lupulus L–enriched diet. The diets lasted 100 weeks. Training was followed over a 25-week period. Bone parameters were measured at week 100. Our results showed that no significant difference was observed among the 4 groups in uterine relative weight, calcium (Ca) intake, fecal Ca, urinary Ca excretion, net Ca absorption, plasma Ca, and bone Ca content. Calcium balance was significantly enhanced in H-NTr rats in comparison with C-NTr and C-Tr rats. Isometric strength training led to a significant increase in total bone mineral density (BMD), diaphyseal BMD, and osteocalcin-deoxypyridinoline ratio in C-Tr rats compared with the other groups. The main findings of the present study indicate that in female rats, a 25-week isometric strength training performed during young adulthood followed by a prolonged no-training period increases BMD values and osteocalcin-deoxypyridinoline ratio, whereas long-term consumption of Humulus lupulus L–enriched diet does not improve bone parameters. It suggests that bone gains induced by exercise do not decrease immediately after cessation of training and also confirms the importance of the practice of physical activity during puberty and young adulthood to maximize the achieved peak bone density.

Molecular impact of clenbuterol and isometric strength training on rat EDL muscles

Clenbuterol, a beta2-adrenergic-receptor agonist, is known to provoke muscle hypertrophy and a slow-to-fast phenotype change. A more glycolytic phenotype should be paralleled by changes in muscle glycolytic metabolism. Two groups (n=16 for each) of 3-month-old male Wistar rats (UCL: untrained clenbuterol, and ECL: exercised clenbuterol) received a chronic administration of clenbuterol (2 mg/kg body weight/day). Two other groups of animals (U: untrained and E: exercised), were given a 0.9% NaCl solution instead of clenbuterol. E and ECL animals followed an 8-week progressive isometric force strength-training program. Both clenbuterol administration and training resulted in an increase in extensor digitorum longus (EDL) mass despite the fact that this muscle was indirectly mobilised during isometric force strength training. Clenbuterol and training induced a consistent slow-to-fast phenotype change without drastically increasing specific activities of glycolytic enzymes. Except for GAPDH and hexokinase, modifications in glycolytic-enzyme-specific activities were not explained by transcriptional changes. Lactate dehydrogenase activity was not affected by clenbuterol but was strongly augmented by training. In EDL of ECL rats, both treatments presented an opposite effect compensating each other. GLUT1 mRNA expression was augmented in EDL of UCL and ECL animals, whereas monocarboxylate transporter 1 mRNA amounts were decreased in EDL of UCL rats. Citrate synthase activity was reduced by clenbuterol treatment but remained unchanged in EDL of E animals. Creatine kinase activity was enhanced only by clenbuterol alone. These data show that clenbuterol-induced muscle hypertrophy and slow-to-fast phenotype changes are not associated with a glycolytic-enzyme-activity increase. They also suggest that in EDL isometric force strength training can reverse clenbuterol-induced molecular adaptations.

Beneficial effects of isometric strength training on endothelial dysfunction in rats

Using female 4-week-old Sprague-Dawley rats, we investigated the effects of 14 weeks of progressive strength isometric training on endothelium dysfunction after estrogen deficiency. We also proposed possible mechanism(s) by which such training acted on endothelium-dependent vasodilation in thoracic aortic rings. Rats were randomly divided into 4 groups of 8 rats: a sham operated group, an ovariectomized sedentary group receiving 17beta-estradiol vehicle s.c. daily, an ovariectomized sedentary group receiving a daily injection of 20 microg.kg(-1) 17beta-estradiol s.c., and an ovariectomized exercised group receiving daily s.c. vehicle. Vascular reactivity of aortic rings have been evaluated by a cumulative dose of acetylcholine (ACh), in the presence or absence of L-NAME (N-nitro-L-arginine methyl ester), indomethacin, thapsigargin, iberiotoxin, apamin, and tetraethylammonium. Ovariectomy markedly decreased the relaxation caused by ACh, whereas 17beta-estradiol treatment induced a significant increase in the relaxation elicited by ACh. Isometric exercise enhanced relaxation due to ACh. This enhancement was attenuated in the presence of L-NAME, indomethacin, thapsigargin, iberiotoxin, and apamin. Our data indicated, for the first time, that the endothelium-dependent relaxant response to ACh was markedly improved in trained ovariectomized rats. This increased vasodilation is mediated by nitric oxide, cyclooxygenase, sarco-endoplasmic reticulum Ca2+-ATPase pathways, and endothelium-derived hyperpolarizing factor. Finally, this study suggested that resistance training may provide benefits in addressing vascular dysfunction consequent to a decline in estrogen levels after menopause. However, any benefits for age-related vascular dysfunction remain to be demonstrated.

Smart Rehabilitation Devices: Part II - Adaptive Motion Control.

This article presents a study of adaptive motion control of smart versatile rehabilitation devices using MR fluids. The device provides both isometric and isokinetic strength training and is reconfigurable for several human joints. Adaptive controls are developed to regulate resistance force based on the prescription of the therapist. Special consideration has been given to the human-machine interaction in the adaptive control that can modify the behavior of the device to account for strength gains or muscle fatigue of the human subject.

Smart Rehabilitation Devices: Part I - Force Tracking Control

Resistance exercise has been widely reported to have positive rehabilitation effects for patients with neuromuscular and orthopaedic conditions. This article presents prototypes of smart variable resistance exercise devices using magneto-rheological fluid dampers. An intelligent supervisory control for regulating the resistive force or torque of the device is developed, and is validated both numerically and experimentally. The device provides both isometric and isokinetic strength training for the human joints including knee, elbow, hip, and ankle.

Effets d'un entraînement isométrique sur la fonction endothéliale de la rate ovariectomisée

Introduction Ovariectomy in animals reduces endothelium-dependent relaxation. On the other hand, endurance training improves the endothelial function. The purpose of this in vivo study was to investigate, in female Sprague–Dawley rats, the effects of a 14-week progressive strength isometric training on endothelium dysfunction induced by estrogen deficiency. Synthesis Rats were randomly divided into 4 groups: 1) sham operated; 2) ovariectomized sedentary group; 3) ovariectomized sedentary group receiving daily injection of 17β-estradiol; 4) ovariectomized exercised group. Vascular reactivity of aortic rings has been evaluated by increasing doses of acetylcholine. The acetylcholine-induced relaxation was enhanced in trained rats. Conclusions Our data indicate that isometric strength training improves endothelial function in ovariectomized female rats.

Adaptive force regulation of muscle strengthening rehabilitation device with magnetorheological fluids

In rehabilitation from neuromuscular trauma or injury, strengthening exercises are often prescribed by physical therapists to recover as much function as possible. Strengthening equipment used in clinical settings range from low-cost devices, such as sandbag weights or elastic bands to large and expensive isotonic and isokinetic devices. The low-cost devices are incapable of measuring strength gains and apply resistance based on the lowest level of torque that is produced by a muscle group. Resistance that varies with joint angle can be achieved with isokinetic devices in which angular velocity is held constant and variable torque is generated when the patient attempts to move faster than the device but are ineffective if a patient cannot generate torque rapidly. In this paper, we report the development of a versatile rehabilitation device that can be used to strengthen different muscle groups based on the torque generating capability of the muscle that changes with joint angle. The device is low cost, is smaller than other commercially available machines, and can be programmed to apply resistance that is unique to a particular patient and that will optimize strengthening. The core of the device, a damper with smart magnetorheological fluids, provides passive exercise force. A digital adaptive control is capable of regulating exercise force precisely following the muscle strengthening profile prescribed by a physical therapist. The device could be programmed with artificial intelligence to dynamically adjust the target force profile to optimize rehabilitation effects. The device provides both isometric and isokinetic strength training and can be developed into a small, low-cost device that may be capable of providing optimal strengthening in the home.

A prototype rehabilitation device with variable resistance and joint motion control

Resistance exercise has been widely reported to have positive rehabilitation effects for patients with neuromuscular and orthopaedic conditions. This paper presents the design of a versatile rehabilitation device in the form of a rotating joint arm mounted on the adjustable seat that provides passive resistance during strength training for muscles. The resistance is supplied by a magnetorheological damper. Intelligent controls are developed to produce resistance force based on the prescription of the therapist. The device provides both isometric and isokinetic strength training and is reconfigurable for several human joints. Special consideration has been given to the human–machine interaction in the adaptive control algorithms that can modify the behavior of the device to account for strength gains or muscle fatigue.

Electromechanical Delay Of The Vastus Medialis During Isometric Strength Training

PURPOSE The present investigation examined electromechanical delay (EMD) in the vastus medialis (VM) following eight weeks of isometric leg extension strength training. METHODS Thirteen adult male volunteers (age19-29) were randomly assigned to a training (TRN) group (n = 6) or a control (CTL) group (n = 7). Electromyographic (EMG) and mechanomyographic (MMG) signals were recorded at the leg extension training angle of 60° of leg flexion. Measurements were collected three times during the study (weeks 0, 4, and 8). The time delay between the onset of EMG activity and MMG activity (EMG-MMG) was recorded along with the time delay between the onset of MMG activity and torque production (MMG-torque). The TRN subjects performed unilateral isometric muscle actions with the non-dominant limb at 60° of leg flexion. The first two weeks, subjects performed two sets of muscle actions at 80% of their maximal isometric PT at 60°. For the remaining six weeks, subjects performed three sets of muscle actions at 80% of their maximal isometric peak torque (PT). Maximal PT was reassessed at the end of the fourth week of training to adjust the training torque values. Each set consisted of ten repetitions lasting six seconds each. The subjects trained three times a week. RESULTS The results indicated significant (p < 0.05) increases in PT for the trained limb of the TRN group between week 0 and week 4 and between week 0 and week 8 of 9.8% and 14.8% respectively. There were no significant changes (p > 0.05) in EMG-MMG delay or MMG-torque delay between the TRN and CTL group and no significant changes (p > 0.05) in EMG-MMG delay or MMG-torque delay found within the TRN group across the training period. CONCLUSION In the present study, delay times between EMG-MMG and MMG-torque in the VM were not significantly altered by eight weeks of isometric training. There was a significant increase in PT following eight weeks of isometric training without significant changes in EMD. It can be speculated that torque production was increased without significant changes in: 1) propagation of action potentials on muscle membrane, 2) excitation/contraction coupling, and/or 3) stretching of the series elastic components by the contractile component since these factors have been previously reported to reflect changes in EMD.

The Effect Of Isometric Strength Training On Electromechanical Delay Of The Vastus Lateralis

PURPOSE To assess the influence of eight weeks of isometric leg extension strength training on electromechanical delay (EMD) of the vastus lateralis. METHODS Electromyographic (EMG) and Mechanomyographic (MMG) signals were recorded on thirteen male subjects (19–29 yrs). Subjects were randomly placed into a control (CG) group (N = 7) or a training (TG) group (N = 6). EMG and MMG signals were recorded at three time points (wks 0, 4, and 8) during leg extension training performed at 60° of leg flexion. The TG performed two sets of unilateral isometric muscle actions at 80% of their maximal isometric peak torque (PT) with the non-dominant leg for the first two weeks. The TG then performed three sets of isometric muscle actions at 80% of their maximal isometric PT for the last six weeks. Training sessions were conducted three days a week and each set of isometric muscle actions included ten 6 s repetitions. The delay in time between the onset of EMG and MMG activity (EMG-MMG) and between the onset of MMG activity and torque production (MMG-torque) were recorded in both TG and CG. RESULTS Participation in eight weeks of isometric leg extension strength training had no influence on EMG-MMG delay or MMG-torque delay within the TG subjects (p > 0.05). No significant differences existed in EMG-MMG delay or MMG-torque delay between the TG and CG subjects (p > 0.05). CONCLUSION These data indicate that eight weeks of isometric training did not significantly influence delay times in EMG-MMG or MMG-torque production in the vastus lateralis. It could be possible that isometric training did not have a significant influence on factors associated with changes in EMD. These factors include action potential propagation, excitation-contraction coupling, and/or stretching of the series elastic components.

Electromechanical Delay Of The Vastus Medialis During Isometric Strength Training

Electromechanical Delay Of The Vastus Medialis During Isometric Strength Training

Angular Differences In The Vastus Lateralis Electromechanical Delay During 8 Weeks Of Isometric Strength Training

PURPOSE The present investigation examined the peak torque (PT), mechanomyographic (MMG), and electromyographic (EMG) responses of the vastus lateralis (VL) to eight weeks of isometric leg extension strength training. METHODS Thirteen adult male volunteers served as subjects and were assigned to a training (TRN) group (n = 6) or a control (CTL) group (n = 7). Maximal isometric muscle actions for leg extension were performed with EMG and MMG activity recorded at leg flexion angles of 30°, 60°, and 90°. Measurements were collected three times during the study (weeks 0, 4, and 8). The time delay between the onset of EMG activity and MMG activity (EMG-MMG) was recorded along with the time delay between the onset of MMG activity and torque production (MMG-torque) and EMG activity and torque production (EMG-torque). RESULTS The delay results indicated no significant differences between the two groups or across the training period in delay times. When the data was collapsed across group and week, a significant (p < 0.05) decrease in MMG-torque delay and EMG-torque delay was found between 90° and 30°. However, no significant (p > 0.05) changes in EMG-MMG delay were found between angles. CONCLUSIONS These findings indicated that changes in muscle length may affect the delay times between MMG-torque and EMG-torque, but may not affect the delay time between EMG-MMG.

Angular Differences In The Vastus Lateralis Electromechanical Delay During 8 Weeks Of Isometric Strength Training

Angular Differences In The Vastus Lateralis Electromechanical Delay During 8 Weeks Of Isometric Strength Training

Rehabilitation device with variable resistance and intelligent control

Resistance exercise has been widely reported to have positive rehabilitation effects for patients with neuromuscular and orthopaedic conditions. This paper presents an optimal design of magneto-rheological fluid dampers for variable resistance exercise device in the form of a knee brace. An intelligent supervisory control for regulating the resistive force or torque of the knee brace has also been studied. The device provides both isometric and isokinetic strength training for the knee.