Effects of isokinetic strength training on concentric and eccentric torque development in the ankle dorsiflexors of older adults

Effects of ankle isokinetic training on muscle strength and balance amongst older women with mild Parkinson's disease: A randomised trial

BACKGROUND

Patients with Parkinson's disease frequently experience problems with balance and gait.

OBJECTIVE

This study examined the influences of regular ankle isokinetic muscle strength training on muscle strength and balance ability amongst elderly women with mild Parkinson's disease.

METHODS

A total of 55 elderly women with mild Parkinson's disease were randomly divided into the experimental group (n= 28) and the control group (n= 27) for 16 weeks. The experimental group was trained for 16 weeks by using isokinetic muscle strength training.

RESULTS

After 16 weeks of training in the experimental group, the peak torque (PT) of ankle (average of the left and right sides) dorsiflexion, plantarflexion, eversion and inversion, and the standing balance index revealed that the left and right stability and overall stability indexes significantly increased by 25.9%, 43.5%, 62.7%, 82.8%, 37.1% and 32.2%, respectively (p< 0.05). The experimental group exhibited significantly increased PT of ankle dorsiflexion, plantarflexion, eversion and inversion. Moreover, the left and right stability and overall stability indexes were significantly improved compared with those of the control group (p< 0.05). This study found a linear regression relationship between the PT of ankle inversion and overall stability index.

CONCLUSION

This study determined that ankle isokinetic muscle strength training improved ankle dorsiflexion, plantarflexion, eversion and inversion muscle strength, and balance ability amongst elderly women with mild Parkinson's disease. However, it did not improve stability in the anterior and posterior directions. Ankle inversion muscle strength is more likely to affect overall balance.

Determining the cortical, spinal and muscular adaptations to strength-training in older adults: A systematic review and meta-analysis

There are observable decreases in muscle strength as a result of ageing that occur from the age of 40, which are thought to occur as a result of changes within the neuromuscular system. Strength-training in older adults is a suitable intervention that may counteract the age-related loss in force production. The neuromuscular adaptations (i.e., cortical, spinal and muscular) to strength-training in older adults are largely equivocal and a systematic review with meta-analysis will serve to clarify the present circumstances regarding the benefits of strength-training in older adults. 20 studies entered the meta-analysis and were analysed using a random-effects model. A best evidence synthesis that included 36 studies was performed for variables that had insufficient data for meta-analysis. One study entered both. There was strong evidence that strength-training increases maximal force production, rate of force development and muscle activation in older adults. There was limited evidence for strength-training to improve voluntary-activation, the volitional-wave and spinal excitability, but strong evidence for increased muscle mass. The findings suggest that strength-training performed between 2 and 12 weeks increases strength, rate of force development and muscle activation, which likely improves motoneurone excitability by increased motor unit recruitment and improved discharge rates.

Effect of Acupuncture on Time-Dependent of Muscle Endurance in Female Elbow Joint: A Randomized Controlled Trial

Immediate characteristics of acupuncture have been confirmed by relevant studies; however, the current study on the time effect of acupuncture in improving upper limb forearm muscle endurance is still limited. The aims of this study are to explore: (1) whether real acupuncture (RA) can improve female forearm muscle endurance compared to sham acupuncture (SA) and (2) whether the changes in forearm muscle endurance after RA are time-dependent. Thirty-six healthy female students were recruited to participate in isokinetic tests of elbow flexion/extension (Flex/Ext) from maximum flexion to maximum extension as much as possible using an isokinetic dynamometer at a speed rate of 60°/sec. Participants in the RA group were stimulated at Quchi (LI11), Shousanli (LI10), Hegu (LI4), Xiaohai (SI8), Tianjing (SJ10), and Waiguan (SJ5) acupoints for 20 min, while the SA group needling was near at these acupoints. The values of the isokinetic parameters and surface electromyography (sEMG) signals were recorded before and after acupuncture. After RA, the isokinetic parameters values (average torque, work, power, and speed), the sEMG values at four major muscles, and the joint stiffness of elbow Flex/Ext were significantly increased (p < 0.05). The enhancement of forearm muscle endurance lasted approximately 7–21 min (from post1 to post3/post4), indicating that the effect of RA to improve elbow Flex/Ext muscle endurance is time-dependent. Therefore, this study found that RA can immediately improve the forearm muscle endurance of healthy women compared with SA, and this effect can last approximately 7–21 min until the acupuncture efficacy decreased or disappeared.

Determining concentric and eccentric force-velocity profiles during squatting

Purpose

The force–velocity relationship of muscular contraction has been extensively studied. However, previous research has focussed either on isolated muscle or single-joint movements, whereas human movement consists of multi-joint movements (e.g. squatting). Therefore, the purpose of this study was to investigate the force–velocity relationship of isovelocity squatting.

Methods

Fifteen male participants (24 ± 2 years, 79.8 ± 9.1 kg, 177.5 ± 6 cm) performed isovelocity squats on a novel motorised isovelocity device (Kineo Training System) at three concentric (0.25, 0.5, and 0.75 m s⁻¹) and three eccentric velocities (− 0.25, − 0.5, and − 0.75 m s⁻¹). Peak vertical ground reaction forces, that occurred during the isovelocity phase, were collected using dual force plates (2000 Hz) (Kistler, Switzerland).

Results

The group mean squat force–velocity profile conformed to the typical in vivo profile, with peak vertical ground reaction forces during eccentric squatting being 9.5 ± 19% greater than isometric (P = 0.037), and occurring between − 0.5 and − 0.75 m s⁻¹. However, large inter-participant variability was identified (0.84–1.62 × isometric force), with some participants being unable to produce eccentric forces greater than isometric. Sub-group analyses could not identify differences between individuals who could/could not produce eccentric forces above isometric, although those who could not tended to be taller.

Conclusions

These finding suggest that variability exists between participants in the ability to generate maximum eccentric forces during squatting, and the magnitude of eccentric increase above isometric cannot be predicted solely based on a concentric assessment. Therefore, an assessment of eccentric capabilities may be required prior to prescribing eccentric-specific resistance training.

The variability of isokinetic ankle strength is different in healthy older men and women

CONTEXT

In the elderly, weak lower limb muscles impair functional tasks' performance.

OBJECTIVE

To evaluate the healthy elderly's ankle dorsiflexion and plantarflexion maximum torque and its variability in two sets of 5 RM isokinetics evaluation.

METHOD

50 women (68.0 ± 4.6 years old) and 50 men (72.7 ± 8.5 years old) did two sets of ankle plantar flexor and dorsiflexor isokinetic tests at 30°/s. Peak torque, total work, and coefficient of variation were analyzed.

RESULTS

Men did the strongest plantarflexion torque (p < 0.05) and dorsiflexion torque (p < 0.05); their highest peak torque occurred at set 2 (p < 0.05), while the largest plantarflexion torque variability (p < 0.05), dorsiflexion torque variability (p < 0.05), and the largest plantarflexion torque variability occurred at set 1 (p < 0.05). Men did the highest plantarflexion and dorsiflexion total work (p < 0.05) at set 2 (p < 0.05).

CONCLUSION

Older men are stronger than older women. The torque variability, in men, was higher during the first set, suggesting an adaptation to the isokinetics evaluation. Clinicians and researchers should consider that different muscles might need different numbers of sets and trials to measure their maximal muscle strength.

Immediate Effects of Acupuncture on Explosive Force Production and Stiffness in Male Knee Joint

Acupuncture can improve explosive force production and affect joint stiffness by affecting muscle activation levels. This study aims to explore the effects of true acupuncture (TA) compared with sham acupuncture (SA) on the explosive force production and stiffness of the knee joint in healthy male subjects. Twenty subjects were randomly divided into the TA group (n = 10) and SA group (n = 10) to complete isokinetic movement of the right knee joint at a speed of 240°/s before and after acupuncture. Futu (ST32), Liangqiu (ST34), Zusanli (ST36), Xuehai (SP10), and Chengshan (BL57) were selected for acupuncture. The intervention of SA is that needles with a blunt tip were pushed against the skin, giving an illusion of insertion. The results showed that acupuncture and the intervention time had a significant interaction effect on knee joint explosive force and joint stiffness (p < 0.05). The average maximum (max) torque, average work, average power, average peak power and total work of the TA group increased significantly after acupuncture (p < 0.05), while the SA group did not (p > 0.05). Therefore, true acupuncture can immediately improve the explosive force and joint stiffness of the male knee joint by inducing post-activation potentiation (PAP) and/or De-Qi.

Strength Training to Prevent Falls in Older Adults: A Systematic Review with Meta-Analysis of Randomized Controlled Trials

We performed a systematic review with meta-analysis of randomized controlled trials (RCTs) to assess the effects of strength training (ST), as compared to alternative multimodal or unimodal exercise programs, on the number of falls in older adults (≥60 years). Ten databases were consulted (CINAHL, Cochrane Library, EBSCO, EMBASE, PEDro, PubMed, Scielo, Scopus, SPORTDiscus and Web of Science), without limitations on language or publication date. Eligibility criteria were as follows: RCTs with humans ≥60 years of age of any gender with one group performing supervised ST and a group performing another type of exercise training, reporting data pertaining falls. Certainty of evidence was assessed with Grading of Recommendations, Assessment, Development and Evaluation (GRADE). Meta-analysis used a random effects model to calculate the risk ratio (RR) for number of falls. Five RCTs with six trials were included (n = 543, 76% women). There was no difference between ST and alternative exercise interventions for falls (RR = 1.00, 95% CI 0.77–1.30, p = 0.99). The certainty of evidence was very low. No dose–response relationship could be established. In sum, ST showed comparable RR based on number of falls in older adults when compared to other multimodal or unimodal exercise modalities, but evidence is scarce and heterogeneous, and additional research is required for more robust conclusions. Registration: PROSPERO CRD42020222908.

Effect of Acupuncture on the Timeliness of Explosive Forces Generated by the Male Shoulder Joint

Athletes aim to improve muscle strength to optimize sports performance and gain a competitive edge. Although modern sports medicine includes rehabilitation treatment methods for improving the explosive force of athletes, including acupuncture, a common alternative therapy, research on the effectiveness of acupuncture in improving the timeliness of explosive forces is limited. There is uncertainty regarding how long the effects of acupuncture treatment persist after treatment. Therefore, the purpose of this study was to explore the effect of acupuncture on the timeliness of explosive forces generated by the male shoulder joint. Eighteen healthy men underwent tests of shoulder adduction/abduction (Add/Abd) and flexion/extension (Flex/Ext) through an isokinetic measurement system. Acupuncture was used to stimulate LU1 (Zhongfu), LU3 (Tianfu), LU4 (Xiabai), LI14 (Binao), SJ13 (Naohui), SJ14 (Jianliao), and SJ12 (Xiaoluo), and the isokinetic parameters were recorded before and after acupuncture. After acupuncture, isokinetic muscle force parameters including the maximum (Max) torque, the average power, the average peak power, the average work, and the total work increased significantly (P < 0.05), whereas the average max torque Abd/Flex did not. Additionally, the preintervention values of the shoulder joints for Add/Abd and Flex/Ext were significantly greater than those at post 1 and post 2 (P < 0.05). The isokinetic results suggest that acupuncture can increase the explosive force of the male shoulder joint Add/Abd and Flex/Ext. Muscle cannot be fully activated when calcium saturation is below the maximal level. In this case, the postactivation potentiation (PAP) may enhance voluntary muscle force production. The effect of acupuncture is time-dependent, that is, the effects of acupuncture gradually weaken and disappear by approximately 10 minutes after acupuncture. Therefore, we suggest that acupuncture is used as an alternative therapy in sports competitions to increase the explosive forces of the shoulder joint, thereby improving sports performance.

Effects of Acupuncture on Explosive Force Production by the Healthy Female Shoulder Joint

Background

Acupuncture is often used to treat chronic conditions, such as pain. In recent years, given the importance of the explosive forces generated by shoulder muscles for the completion of motor tasks, studies in which nerves were stimulated through acupuncture to increase the explosive forces were conducted. This study explored the effect of acupuncture on explosive force production by the muscles of the female shoulder joint.

Methods

Eighteen healthy women underwent shoulder adduction (Add), abduction (Abd), flexion (Flex), and extension (Ext) tests with an isokinetic measurement system. Acupuncture was used to stimulate the Zhongfu (LU1), Tianfu (LI3), Xiabai (LU4), Binao (LI14), Naohui (SJ13), Jianliao (SJ14), and Xiaoluo (SJ12) points, and electromyography (EMG) signals were recorded before and after acupuncture.

Results

After acupuncture, there was a significant difference in the average maximum work, the average maximum power, the average maximum speed, the total work in Add/Abd and Flex/Ext, the EMG signals, and the stiffness of the muscles in Abd and Ext (P < 0.05). There were no significant differences in the average maximum torque in Abd or Flex.

Conclusion

Based on the results, there may be a significant correlation between the manipulation of different acupoints by acupuncture and the average maximum torque and stiffness. Acupuncture may stimulate nerves to activate muscles and induce a postactivation potentiation effect that improves explosive force production. Therefore, acupuncture as an auxiliary tool may increase the explosive forces generated by acupoint-related muscles by stimulating nerves.

Effect of Acupuncture on Muscle Endurance in the Female Shoulder Joint: A Pilot Study

Shoulder joint dysfunction is the leading cause of decreased athletic ability in athletes. Shoulder joint sports injuries affect the athletic performance of athletes. Improvements in the muscle endurance of the shoulder joint can reduce the incidence of shoulder joint dysfunction. Acupuncture has been an important part of Asian culture for a long time. In acupuncture, nerves are stimulated, inducing postactivation potentiation (PAP) in the body's motor units and enhancing muscle strength. In this research, 20 female participants with full flexion/extension and adduction/abduction ranges of motion in the shoulder joint during isokinetic exercises underwent stimulation of the following acupuncture points in the shoulder joint: Binao (LI14), Jianyu (LI15), Jianliao (SJ14), Naohui (SJ13), Yuzhong (KI26), Zhongfu (LU1), Yunmen (LU2), Xiabai (LU4), Chize (LU5), Tianfu (LU3), and Xiaoluo (SJ12). In the study, there were significant increases after acupuncture in the average maximum torque in flexion, extension, and adduction; the average work in flexion/extension and adduction/abduction; the average power in flexion/extension and adduction/abduction; the total work in flexion/extension and adduction/abduction; the total net sagittal-plane work (flexion + extension); and the total net frontal-plane work (adduction + abduction) (P < 0.05). The average maximum abduction torque did not increase significantly, potentially due to antagonistic forces of muscles. Therefore, acupuncture at acupoints around the shoulder joint can increase muscle excitability, thereby delaying muscle fatigue and increasing muscle endurance.

Effects of High-Intensity Interval Training and Isoinertial Training on Leg Extensors Muscle Function, Structure, and Intermuscular Adipose Tissue in Older Adults

We compared the effects of aerobic high-intensity training (HIT) and isoinertial resistance training (IRT) on the strength, mass, architecture, intermuscular adipose tissue (IMAT) quality, and neuromuscular activation of the quadriceps in elderly subjects. Twelve healthy men (69.3 ± 4.2 years; 77.8 ± 10.4 kg; 1.72 ± 0.05 m) were exposed to 8 weeks of HIT (7 × 2-min cycling repetitions at 90% of V.O_2peak, 3 times/week) and, after 4 months (detraining), to IRT (4 × 7 maximal concentric–eccentric knee extensions, 3 times/week). Before and after trainings, we measured knee extension isometric (T_MVC) and dynamic (T_C) maximal concentric torque, anatomical cross-sectional area (ACSA) at 25, 50, and 75% of femur length, quadriceps volume (Vol), IMAT, pennation angle (θ_p) of the fibers from the vastus lateralis, and voluntary activation (%Act). T_MVC and T_C were significantly larger only after IRT (P = 0.008); IRT was able to elicit a greater increase of ACSA than HIT; Vol increases similarly and significantly after HIT and IRT (P = 0.003–0.001); IMAT at 50% of femur length decreased after both HIT and IRT (P = 0.001–0.003); physiological cross-sectional area (PCSA) was larger after IRT than before (P = 0.025); specific torque did not change throughout the study (45.5 N cm^–2 ± 12.0); %Act of the quadriceps was significantly affected only by IRT (P = 0.011). Both HIT and IRT are able to elicit beneficial modifications of muscular mass, architecture, and quality (reducing IMAT) in elderly subjects in connection with an amelioration of strength. HIT and IRT caused a homogeneous increase of ACSA and of Vol of the quadriceps. PCSA increases, but specific strength per unit of PCSA did not change. The increases of functional torque seemed to be attributed to a parallel increase of %Act and muscle hypertrophy only after IRT. Data suggest that IMAT may be a prominent indicator to track metabolic-dependent activity and skeletal muscle quality.

Design and control of a bio-inspired soft wearable robotic device for ankle-foot rehabilitation

We describe the design and control of a wearable robotic device powered by pneumatic artificial muscle actuators for use in ankle-foot rehabilitation. The design is inspired by the biological musculoskeletal system of the human foot and lower leg, mimicking the morphology and the functionality of the biological muscle-tendon-ligament structure. A key feature of the device is its soft structure that provides active assistance without restricting natural degrees of freedom at the ankle joint. Four pneumatic artificial muscles assist dorsiflexion and plantarflexion as well as inversion and eversion. The prototype is also equipped with various embedded sensors for gait pattern analysis. For the subject tested, the prototype is capable of generating an ankle range of motion of 27° (14° dorsiflexion and 13° plantarflexion). The controllability of the system is experimentally demonstrated using a linear time-invariant (LTI) controller. The controller is found using an identified LTI model of the system, resulting from the interaction of the soft orthotic device with a human leg, and model-based classical control design techniques. The suitability of the proposed control strategy is demonstrated with several angle-reference following experiments.

Ankle strength and force sense after a progressive, 6-week strength-training program in people with functional ankle instability

CONTEXT

Although strength training is commonly used to rehabilitate ankle injuries, studies investigating the effects of strength training on proprioception have shown conflicting results.

OBJECTIVE

To determine the effects of a 6-week strength-training protocol on force sense and strength development in participants with functional ankle instability.

DESIGN

Randomized controlled clinical trial.

SETTING

University athletic training research laboratory.

PATIENTS OR OTHER PARTICIPANTS

A total of 40 participants with functional ankle instability were recruited. They were randomly placed into a training group (10 men, 10 women: age = 20.9 ± 2.2 years, height = 76.4 ± 16.1 cm, mass = 173.0 ± 7.9 kg) or control group (10 men, 10 women: age = 20.2 ± 2.1 years, height = 78.8 ± 24.5 cm, mass = 173.7 ± 8.2 kg).

INTERVENTION(S)

Participants in the training group performed strength exercises with the injured ankle 3 times per week for 6 weeks. The protocol consisted of a combination of rubber exercise bands and the Multiaxial Ankle Exerciser, both clinically accepted strengthening methods for ankle rehabilitation. The progression of this protocol provided increasingly resistive exercise as participants changed either the number of sets or resistance of the Thera-Band or Multiaxial Ankle Exerciser. Main Outcome Measure(s): A load cell was used to measure strength and force sense. Inversion and eversion strength was recorded to the nearest 0.01 N. Force-sense reproduction was measured at 2 loads: 20% and 30% of maximal voluntary isometric contraction.

RESULTS

Increases in inversion (F(1,38) = 11.59, P < 0.01, η(p)(2) = 0.23, power = 0.91) and eversion (F(1,38) = 57.68, P < .01, η(p)(2) = 0.60, power = 0.99) strength were found in the training group at the posttest when compared with the control group. No significant improvements were noted in force-sense reproduction for either group.

CONCLUSIONS

Strength training at the ankle increased strength but did not improve force sense.

Reliability of ankle isometric, isotonic, and isokinetic strength and power testing in older women

BACKGROUND

Ankle strength (force-generating capacity) and power (work produced per unit of time or product of strength and speed) capabilities influence physical function (eg, walking, balance) in older adults. Although strength and power parameters frequently are measured with dynamometers, few studies have examined the reliability of measurements of different types of contractions.

OBJECTIVE

The purpose of this study was to examine relative and absolute intrarater reliability of isometric, isotonic, and isokinetic ankle measures in older women.

DESIGN

This was a prospective, descriptive methodological study.

METHODS

The following dorsiflexion (DF) and plantar-flexion (PF) measures were assessed twice (7 days apart) by the same examiner in 30 older women (mean age=73.3 years, SD=4.7): isometric peak torque and rate of torque development (RTD), isotonic peak velocity, average acceleration and peak power, and isokinetic peak torque and peak power (30 degrees/s and 90 degrees/s). Several statistical methods were used to examine relative and absolute reliability.

RESULTS

Intraclass correlation coefficients (ICCs) for the DF tests (ICC=.76-.97) were generally higher than ICCs for matched PF tests (ICC=.58-.93). Measures of absolute reliability (eg, coefficient of variation of the typical error [CV(TE)]) also demonstrated more reliable values for DF tests (5%-18%) compared with PF tests (7%-37%). Isotonic peak velocity tests at minimal loads were associated with the lowest CV(TE) and ratio limits of agreement values for both DF (5% and 14%, respectively) and PF (7% and 18%, respectively). Isometric RTD variables were the least reliable (CV(TE)=16%-37%).

LIMITATIONS

This study was limited to a relatively homogeneous sample of older women.

CONCLUSIONS

Test-retest reliability was adequate for determining changes at the group level for all strength and power variables except isometric RTD. Minimal detectable change scores were determined to assist clinicians in assessing meaningful change over time in ankle strength and power measurements within individuals.

Effects of 8 weeks of balance or weight training for the independently living elderly on the outcomes of induced slips

The study was conducted to evaluate whether the balance or weight training could alter gait characteristics of elderly contributing to a reduction in the likelihood of slip-induced falls. A total of 18 elderly were evaluated for the study. The results indicated decreases in heel contact velocities and the friction demand characteristics after 8 weeks of training, although fundamental gait characteristics, such as walking velocity and step length, were not changed. The results also indicated an increase in transitional acceleration of the whole body center of mass. The number of falls after 8 weeks was reduced in training groups. These findings were found in conjunction with the improvements in knee flexor muscle and plantarflexor muscle strength. In conclusion, after training, elderly were less likely to initiate slips and more likely to recover from slips.

Progressive resistance strength training for improving physical function in older adults

BACKGROUND

Muscle weakness in old age is associated with physical function decline. Progressive resistance strength training (PRT) exercises are designed to increase strength.

OBJECTIVES

To assess the effects of PRT on older people and identify adverse events.

SEARCH STRATEGY

We searched the Cochrane Bone, Joint and Muscle Trauma Group Specialized Register (to March 2007), the Cochrane Central Register of Controlled Trials (The Cochrane Library 2007, Issue 2), MEDLINE (1966 to May 01, 2008), EMBASE (1980 to February 06 2007), CINAHL (1982 to July 01 2007) and two other electronic databases. We also searched reference lists of articles, reviewed conference abstracts and contacted authors.

SELECTION CRITERIA

Randomised controlled trials reporting physical outcomes of PRT for older people were included.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected trials, assessed trial quality and extracted data. Data were pooled where appropriate.

MAIN RESULTS

One hundred and twenty one trials with 6700 participants were included. In most trials, PRT was performed two to three times per week and at a high intensity. PRT resulted in a small but significant improvement in physical ability (33 trials, 2172 participants; SMD 0.14, 95% CI 0.05 to 0.22). Functional limitation measures also showed improvements: e.g. there was a modest improvement in gait speed (24 trials, 1179 participants, MD 0.08 m/s, 95% CI 0.04 to 0.12); and a moderate to large effect for getting out of a chair (11 trials, 384 participants, SMD -0.94, 95% CI -1.49 to -0.38). PRT had a large positive effect on muscle strength (73 trials, 3059 participants, SMD 0.84, 95% CI 0.67 to 1.00). Participants with osteoarthritis reported a reduction in pain following PRT(6 trials, 503 participants, SMD -0.30, 95% CI -0.48 to -0.13). There was no evidence from 10 other trials (587 participants) that PRT had an effect on bodily pain. Adverse events were poorly recorded but adverse events related to musculoskeletal complaints, such as joint pain and muscle soreness, were reported in many of the studies that prospectively defined and monitored these events. Serious adverse events were rare, and no serious events were reported to be directly related to the exercise programme.

AUTHORS' CONCLUSIONS

This review provides evidence that PRT is an effective intervention for improving physical functioning in older people, including improving strength and the performance of some simple and complex activities. However, some caution is needed with transferring these exercises for use with clinical populations because adverse events are not adequately reported.

The aging population--is there a role for endocrine interventions?

The expected increase in the aging population will have a significant impact on society and the health system in the coming years and decades. Enhancing healthspan, "healthy aging", and thus extending the time that the elderly are able to function independently is a significant task and is imperative. Age-dependent changes such as weight loss, sarcopenia and anorexia, which contribute to the development of frailty in the elderly are discussed. The role of the age-dependent decrease in growth hormone secretion in this process and the potential benefits and risks of hormonal interventions to delay, prevent or reverse frailty in the elderly are reviewed.

Eccentric exercise in patients with chronic health conditions: a systematic review

PURPOSE

The capacity of eccentric actions to produce muscle hypertrophy, strength gains, and neural adaptations without stressing the cardiopulmonary system has led to the prescription of eccentric training programmes in patients with low tolerance to exercise, such as elders or those with chronic health conditions. The purpose of this systematic review was to analyze the evidence regarding the effectiveness and suitability of eccentric training to restore musculoskeletal function in patients with chronic diseases.

SUMMARY OF KEY POINTS

Relevant articles were identified from nine databases and from the reference lists of key articles. Articles were assessed to determine level of evidence and scientific rigour. Nine studies met the inclusion criteria. According to Sackett's levels of evidence, 7 studies were graded at level IIb, 1 study at level IV, and the remaining study at level V. Articles were also graded for scientific rigour according to the PEDro scale. One study was rated as high quality, 4 studies were rated as moderate, and 2 studies were graded as poor quality.

CONCLUSIONS

Eccentric training may be safely used to restore musculoskeletal function in patients with some specific chronic conditions. However, the heterogeneity of diseases makes it very difficult to extrapolate results and to standardize clinical recommendations for adequate implementation of this type of exercise. More studies are needed to establish the potential advantages of eccentric training in chronic conditions.

Increased central facilitation of antagonist reciprocal inhibition at the onset of dorsiflexion following explosive strength training

At the onset of dorsiflexion disynaptic reciprocal inhibition (DRI) of soleus motoneurons is increased to prevent activation of the antagonistic plantar flexors. This is caused by descending facilitation of transmission in the DRI pathway. Because the risk of eliciting stretch reflexes in the ankle plantar flexors at the onset of dorsiflexion is larger the quicker the movement, it was hypothesized that DRI may be increased when subjects are trained to perform dorsiflexion movements as quickly as possible For this purpose, 14 healthy human subjects participated in explosive strength training of the ankle dorsiflexor muscles 3 times a week for 4 wk. Test sessions were conducted before, shortly after, and 2 wk after the training period. The rate of torque development measured at 30, 50, 100, and 200 ms after onset of voluntary explosive isometric dorsiflexion increased by 24–33% ( P < 0.05). DRI was measured as the depression of the soleus H reflex following conditioning stimulation of the peroneal nerve (1.1 × motor threshold) at an interval of 2–3 ms. At the onset of dorsiflexion the amount of DRI measured relative to DRI at rest increased significantly from 6% before the training to 22% after the training ( P < 0.05). We speculate that DRI at the onset of movement may be increased in healthy subjects following explosive strength training to ensure efficient suppression of the antagonist muscles as the dorsiflexion movement becomes faster.

Complex myograph allows the examination of complex muscle contractions for the assessment of muscle force, shortening, velocity, and work in vivo

Background

The devices used for in vivo examination of muscle contractions assess only pure force contractions and the so-called isokinetic contractions. In isokinetic experiments, the extremity and its muscle are artificially moved with constant velocity by the measuring device, while a tetanic contraction is induced in the muscle, either by electrical stimulation or by maximal voluntary activation. With these systems, experiments cannot be performed at pre-defined, constant muscle length, single contractions cannot be evaluated individually and the separate examination of the isometric and the isotonic components of single contractions is not possible.

Methods

The myograph presented in our study has two newly developed technical units, i.e. a). a counterforce unit which can load the muscle with an adjustable, but constant force and b). a length-adjusting unit which allows for both the stretching and the contraction length to be infinitely adjustable independently of one another. The two units support the examination of complex types of contraction and store the counterforce and length-adjusting settings, so that these conditions may be accurately reapplied in later sessions.

Results

The measurement examples presented show that the muscle can be brought to every possible pre-stretching length and that single isotonic or complex isometric-isotonic contractions may be performed at every length. The applied forces act during different phases of contraction, resulting into different pre- and after-loads that can be kept constant – uninfluenced by the contraction. Maximal values for force, shortening, velocity and work may be obtained for individual muscles. This offers the possibility to obtain information on the muscle status and to monitor its changes under non-invasive measurement conditions.

Conclusion

With the Complex Myograph, the whole spectrum of a muscle's mechanical characteristics may be assessed.

Maximum voluntary joint torque as a function of joint angle and angular velocity: model development and application to the lower limb

Measurements of human strength can be important during analyses of physical activities. Such measurements have often taken the form of the maximum voluntary torque at a single joint angle and angular velocity. However, the available strength varies substantially with joint position and velocity. When examining dynamic activities, strength measurements should account for these variations. A model is presented of maximum voluntary joint torque as a function of joint angle and angular velocity. The model is based on well-known physiological relationships between muscle force and length and between muscle force and velocity and was tested by fitting it to maximum voluntary joint torque data from six different exertions in the lower limb. Isometric, concentric and eccentric maximum voluntary contractions were collected during hip extension, hip flexion, knee extension, knee flexion, ankle plantar flexion and dorsiflexion. Model parameters are reported for each of these exertion directions by gender and age group. This model provides an efficient method by which strength variations with joint angle and angular velocity may be incorporated into comparisons between joint torques calculated by inverse dynamics and the maximum available joint torques.

Adaptations to long-term strength training of ankle joint muscles in old age

The aim of this study was to enquire whether older adults, who continue plantar-flexion (PF) strength training for an additional 6-month period, would achieve further improvements in neuromuscular performance, in the ankle PFs, and in the antagonist dorsi-flexors (DFs). Twenty-three healthy older volunteers (mean age 77.4 +/- 3.7 years) took part in this investigation and 12 of them followed a 1-year strength-training program. Both neural and muscular factors were examined during isometric maximal voluntary contraction (MVC) torques in ankle PF and DF pre-training, post 6 and post 12 months. The main finding was that 6 months of additional strength training of the PFs, beyond 6 months, allowed further improvements in neuromuscular performance at the ankle joint in older adults. Indeed, during the first 6 months of progressive resistance training, there was an increase in the PF MVC torque of 11.1 +/- 19.9 N m, and then of 11.1 +/- 17.9 N m in the last 6-month period. However, it was only after 1 year that there was an improvement in the evoked contraction at rest in PF (+ 8%). The strength training of the agonist PF muscles appeared to have an impact on the maximal resultant torque in DF. However, it appeared that this gain was first due to modifications occurring in the trained PFs muscles, then, it seemed that the motor drive of the DFs per se was altered. In conclusion, long-term strength training of the PFs resulted in continued improvements in neuromuscular performance at the ankle joint in older adults, beyond the initial 6 months.

Effect of high-intensity strength-training on functional measures of balance ability in balance-impaired older adults

OBJECTIVE

The aim of this study was to evaluate the effect of a 10-week, high-intensity strength-training program targeting key lower extremity muscles for the purpose of improving postural control in balance-impaired older adults.

METHODS

A quasi-experimental, delayed entry controlled design was used to evaluate balance ability in balance-impaired older adults after participation in 10 weeks of high-intensity strength training focused on the quadriceps, hamstrings, tibialis anterior, and gastrocnemius muscles. Participants were evaluated using validated clinical measures of functional balance ability: the Berg Balance Scale, the Timed Up and Go, and the Activities-Specific Balance Confidence Scale.

RESULTS

After strength training, the exercisers were significantly stronger than the control subjects. They improved significantly on the Berg Balance Scale (P = .030) from a mean score of 48.8 +/- 2.4 of 56 before training to 51.2 +/- 4.3 of 56 after training. The Timed Up and Go (P = .045) and the Activities-Specific Balance Confidence Scale (P = .038) also improved significantly in the experimental group. These changes are associated with a decrease in fall risk.

CONCLUSIONS

High-intensity strength training can safely and effectively strengthen lower extremity muscles in balance-impaired older adults, resulting in significant improvements in functional balance ability and decreased fall risk.

Ankle force and rate of force production increase following high intensity strength training in frail older adults

BACKGROUND AND AIMS

The most common cause of accidental injury and death in people over age 65 results from impacts associated with falling. Balance impaired older adults have poorer balance control than healthy young adults or healthy older adults. Lack of sufficient lower extremity strength and inability to rapidly produce muscle force may contribute to diminished balance control in the elderly. This study evaluated the effect of a 10-week high intensity strength-training program targeting key lower extremity muscles for the purpose of improving postural control in frail older adults.

METHODS

Thirteen experimental and fourteen control subjects, all balance impaired older adults were evaluated in response to unexpected platform perturbations that simulated slips.

RESULTS

Following strength training the experimental group was significantly stronger than the control group. Mean ankle moments improved in the experimental group following strength training during forward sway (Right: p=0.067, Left: p=0.009) and backward sway (Right: p=0.031, Left: p=0.058). For the backward sway condition the ankle rate of torque production increased significantly in the experimental group (Right: p=0.016, Left: p=0.031).

CONCLUSIONS

Enhancement of lower extremity strength contributed to improvements in balance stability demonstrated by greater ankle force production, in response to balance threats.

Knee extensor and flexor torque development with concentric and eccentric isokinetic training

This study assessed muscular torque and rate of torque development following concentric (CON) or eccentric (ECC) isokinetic training. Thirty-eight women were randomly assigned to either CON or ECC training groups. Training consisted of knee extension and flexion of the nondominant leg three times per week for 20 weeks (SD = 1). Eccentric training increased ECC knee extension and flexion peak torque more than CON training. The ECC group improved acceleration time and time to peak torque with ECC movements versus the CON group. Slow-velocity ECC isokinetic training yielded greater ECC and similar CON torque development gains versus CON training over the course of 20 weeks in young women.

Resistance training effects on muscular strength of elderly are related to intensity and gender

The purpose of this study was to determine whether a high intensity (HI) versus a moderate (MI) or low-intensity (LI) training program would be more effective in improving the isokinetic knee extension muscular performance in healthy inactive men and women. Sixty-four participants, men and women, were randomly assigned to one of four groups: control group (C), LI (50% of 1RM), the MI group (70% of 1RM) and the HI (90% of 1RM). Participants exercised on three resistance exercise machines: leg extension, leg curls and leg press. The isokinetic testing method (concentric mode) applied prior to and at the end of the training period (16 weeks, three 3 times per week) to assess the knee muscular performance. MANOVA repeated measures revealed that the HI group demonstrated the most strength gains following a speed specificity pattern (most considerable improvement occurred at or near slow speeds from 7.3% to 11.2% for male and from 2.3% to 15.2% for female). In addition, males demonstrated a greater improvement of knee extension power output than females. In conclusion, HI strength training is proposed for elderly men and women as the most effective protocol. Furthermore only at low-velocity testing, women of the HI showed a greater change than men (p < 0.05). Regarding strength increase in relation to various testing velocities, a greater increase was found in HI at low velocities, with the other training groups exhibiting almost similar strength increase at all tested speeds.

Plasticity of dynamic muscle performance with strength training in elderly humans

Data are scarce relating to the plasticity with strength training of dynamic muscle performance in older humans. Hence, we investigated alterations in the torque-velocity relation with strength training in old age, and their origin. Knee extension and leg-press exercises were performed three times per week for 14 weeks. Maximal isokinetic knee extension torque was assessed during concentric and eccentric muscle actions. Agonist-antagonist muscle activation was assessed using electromyography. Vastus lateralis muscle architecture was examined in vivo using ultrasonography. Training increased concentric torque by 22-37% (P < 0.01), but failed to alter eccentric torque (P > 0.05). Increased agonist muscle activation, increased muscle fascicle lengths, and greater elastic energy recovered from tendinous structures may explain the adaptations during concentric actions, whereas the failure of eccentric torque to increase might be explained by the preservation of eccentric force with aging and an underloading of the eccentric movement phase during training. These findings may have important implications for dynamic muscle performance in old age.

Human soleus muscle protein synthesis following resistance exercise

AIM

It is generally believed the calf muscles in humans are relatively unresponsive to resistance training when compared with other muscles of the body. The purpose of this investigation was to determine the muscle protein synthesis response of the soleus muscle following a standard high intensity bout of resistance exercise.

METHODS

Eight recreationally active males (27 +/- 4 years) completed three unilateral calf muscle exercises: standing calf press/heel raise, bent-knee calf press/heel raise, and seated calf press/heel raise. Each exercise consisted of four sets of 15 repetitions (approximately 15 repetition maximum, RM, or approximately 70% 1RM). Fractional rate of muscle protein synthesis (FSR) was determined with a primed constant infusion of [2H5]phenylalanine coupled with muscle biopsies immediately and 3 h following the exercise in both the exercise and non-exercise (resting control) leg.

RESULTS

FSR was elevated (P < 0.05) in the exercise (0.069 +/- 0.010) vs. the control (0.051 +/- 0.012) leg. Muscle glycogen concentration was lower (P < 0.05) in the exercise compared with the control leg (Decrease from control; immediate post-exercise: 54 +/- 5; 3 h post-exercise: 36 +/- 4 mmol kg(-1) wet wt.). This relatively high amount of glycogen use is comparable with previous studies of resistance exercise of the thigh (i.e. vastus lateralis; approximately 41-49 mmol kg(-1) wet wt.). However, the exercise-induced increase in FSR that has been consistently reported for the vastus lateralis (approximately 0.045-0.060% h(-1)) is on average approximately 200% higher than reported here for the soleus (0.019 +/- 0.003% h(-1)).

CONCLUSIONS

These results suggest the relatively poor response of soleus muscle protein synthesis to an acute bout of resistance exercise may be the basis for the relative inability of the calf muscles to respond to resistance training programs.

Transfer of resistance training to enhance rapid coordinated force production by older adults

The purpose of this study was to examine the capacity of resistance training to enhance the rapid and coordinated production of force by older people. Thirty adults (> or =60 years) completed a visually guided aiming task that required the generation of isometric torque in 2 df about the elbow prior to and following a 4-week training period. Groups of six participants were allocated to two progressive (40-100% maximal voluntary contraction (MVC)) resistance-training (PRT) groups, to two constant low-load (10% MVC) training groups (CLO) and to one no-training control group. Training movements required the generation of either combined flexion and supination (FLESUP), or combined extension and supination (EXTSUP). In response to training, target acquisition times in the aiming task decreased for all groups; however, both the nature of the training load and the training movement influenced the pattern and magnitude of improvements (EXTSUP_CLO: 36%, FLESUP_PRT 26%, EXTSUP_PRT 22%, FLESUP_CLO 20%, CONTROL 15%). For one group that trained with progressively increasing loads, there arose a subsequent decrease in performance in one condition of the transfer task. For each group, these adaptations were accompanied by systematic changes in the coordination of muscles about the elbow joint, particularly the biceps brachii.

The Consequences of Resistance Training for Movement Control in Older Adults

Older adults who undertake resistance training are typically seeking to maintain or increase their muscular strength with the goal of preserving or improving their functional capabilities. The extent to which resistance training adaptations lead to improved performance on tasks of everyday living is not particularly well understood. Indeed, studies examining changes in functional task performance experienced by older adults following periods of resistance training have produced equivocal findings. A clear understanding of the principles governing the transfer of resistance training adaptations is therefore critical in seeking to optimize the prescription of training regimes that have as their aim the maintenance and improvement of functional movement capacities in older adults. The degenerative processes that occur in the aging motor system are likely to influence heavily any adaptations to resistance training and the subsequent transfer to functional task performance. The resulting characteristics of motor behavior, such as the substantial decline in the rate of force development and the decreased steadiness of force production, may entail that specialized resistance training strategies are necessary to maximize the benefits for older adults. In this review, we summarize the alterations in the neuromuscular system that are responsible for the declines in strength, power, and force control, and the subsequent deterioration in the everyday movement capabilities of older adults. We examine the literature concerning the neural adaptations that older adults experience in response to resistance training, and consider the readiness with which these adaptations will improve the functional movement capabilities of older adults.

The contribution of reactive oxygen species to sarcopenia and muscle ageing

Ageing is a complex process that in muscle in usually associated with a decrease in mass, strength, and velocity of contraction. One of the most striking effects of ageing on muscle is known as sarcopenia, a process that is the result of many cellular changes, such as a reduction in the number of motor units coupled with an increase in motor unit size, progressive denervation, decreased synthesis of myofibrillar components, atrophy due to disuse, accumulation of connective tissue, etc. It has been suggested that sarcopenia may be triggered by reactive oxygen species (ROS) that have accumulated throughout one's lifetime. ROS, which are generated by the addition of a single electron to the oxygen molecule, are formed in all tissues including muscle fibres and, especially, in the mitochondrial respiratory chain. Such reactive elements are usually quite harmful and result in oxidative stress that can damage other cellular components such as DNA, proteins, lipids, etc. resulting in further damage to the cells and tissues. As a consequence, the intra and intercellular membranes of the muscle fibers, in particular those of the Sarcoplasmic reticulum, may be modified and the Ca(2+) transport mechanism altered. During the ageing process ROS production may drastically increase because of an altered function of the respiratory chain and an insufficient functioning of the antioxidant cellular defences. How such an oxidative insult plays a role in the age-related decrease of muscle performance and mass has yet to be defined. What does have a clear role in the progression of sarcopenia is the significant reduction of the regenerative potential of muscle fibres. This reduction is due to a reduced pool of satellite cells that are usually recruited to replace damaged fibres and promote their regeneration. Exercise as a method to prevent or at least delay sarcopenia has been discussed in many scientific reports. While on the one hand, it seems clear that exercise is effective in reducing the loss of muscle mass, on the other it appears that physical activity increases both the mechanical damage and the accumulation of free radicals as a result of an increase in the aerobic metabolism of the muscles involved.

Molecular basis of skeletal muscle plasticity--from gene to form and function

Skeletal muscle shows an enormous plasticity to adapt to stimuli such as contractile activity (endurance exercise, electrical stimulation, denervation), loading conditions (resistance training, microgravity), substrate supply (nutritional interventions) or environmental factors (hypoxia). The presented data show that adaptive structural events occur in both muscle fibres (myofibrils, mitochondria) and associated structures (motoneurons and capillaries). Functional adaptations appear to involve alterations in regulatory mechanisms (neuronal, endocrine and intracellular signalling), contractile properties and metabolic capacities. With the appropriate molecular techniques it has been demonstrated over the past 10 years that rapid changes in skeletal muscle mRNA expression occur with exercise in human and rodent species. Recently, gene expression profiling analysis has demonstrated that transcriptional adaptations in skeletal muscle due to changes in loading involve a broad range of genes and that mRNA changes often run parallel for genes in the same functional categories. These changes can be matched to the structural/functional adaptations known to occur with corresponding stimuli. Several signalling pathways involving cytoplasmic protein kinases and nuclear-encoded transcription factors are recognized as potential master regulators that transduce physiological stress into transcriptional adaptations of batteries of metabolic and contractile genes. Nuclear reprogramming is recognized as an important event in muscle plasticity and may be related to the adaptations in the myosin type, protein turnover, and the cytoplasma-to-myonucleus ratio. The accessibility of muscle tissue to biopsies in conjunction with the advent of high-throughput gene expression analysis technology points to skeletal muscle plasticity as a particularly useful paradigm for studying gene regulatory phenomena in humans.

Progressive resistance strength training for physical disability in older people

BACKGROUND

Muscle weakness in old age, is associated with physical disability and an increased risk of falls. Progressive resistance strength (PRT) training exercises (i.e. movements performed against a specific external force that is regularly increased during training) are designed to increase strength in older people.

OBJECTIVES

To assess the effect of PRT on measures of physical disability, functional limitation and impairment in older people, and identify adverse events.

SEARCH STRATEGY

We searched the Cochrane Musculoskeletal Injuries Group specialized register (to August 2002), CENTRAL/CCTR (The Cochrane Library Issue 2, 2002), MEDLINE (1966 to February 1, 2002), EMBASE (1980 to February 1, 2002), CINAHL (1982 to February 1, 2002), Sports Discus (1948 to February 1, 2002), PEDro - The Physiotherapy Evidence Database (accessed February 1, 2002) and Digital Dissertations (accessed February 1, 2002). We also searched reference lists of articles, reviewed conference abstracts and contacted authors.

SELECTION CRITERIA

Randomised trials of PRT alone for older people (i.e. mean age of 60 or over) were included.

DATA COLLECTION AND ANALYSIS

Two reviewers independently assessed trial quality and extracted data. Weighted mean differences (WMD) were obtained using fixed or random effect models as appropriate. When measures with different units were pooled, standardised mean differences (SMD) were calculated. Relative risks were calculated for dichotomous outcomes.

MAIN RESULTS

Sixty-six trials with 3783 participants were included. Most studies were small and of poor quality. PRT had a large positive effect on strength (41 trials, 1955 participants), but there was statistical heterogeneity that was not explained by differences in study quality, participant characteristics or the exercise program. Some functional limitation measures showed modest improvements (i.e. gait speed, 14 trials, 798 participants, WMD 0.07 m/s, 95% CI 0.04 to 0.09). However, there was no evidence that PRT had an effect on physical disability when activity measures or health related quality of life measures (HRQOL) were assessed (10 trials, 798 participants, SMD 0.01, 95% CI -0.14 to 0.16 ). Adverse events were poorly recorded, but musculoskeletal injuries were detected in most of the studies that prospectively defined and monitored these events.

REVIEWER'S CONCLUSIONS

PRT appears to be an effective intervention to increase strength in older people and has a positive effect on some functional limitations. However, the effect of this intervention on more substantive outcomes such as measures of disability or HRQOL remains unclear. It is difficult to determine the balance of risks and benefits of PRT because adverse events have generally been poorly collected and recorded.

Ankle plantar flexion strength in resistance and endurance trained middle-aged adults

Maximum concentric (CONC) and eccentric (ECC) strength of the ankle plantar flexor muscles were compared between middle-aged adults who regularly participated in resistance exercise training versus those who participated in weight-bearing endurance exercise. A total of 40 men and women with a mean age of 48.9 years (SD = 5.3) were tested for CONC and ECC plantar flexor (PF) strength, using an isokinetic device at 3 velocities: 30, 90 and 180 degrees/s. Mean strength values for the groups of men and women involved in resistance exercise were consistently higher than those involved in the endurance training for the CONC tests, where values ranged from 35% to 46% (avg. 41%, p < .01), but less between-group difference was observed for the ECC loading condition: 4% to 30% (avg. 18%). Thus ECC/CONC ratios, which rose with increasing velocity, were consistently higher for the endurance group vs. resistance-trained. Finally, since concentric PF torque values were found to be quite low for the middle-aged women who did only endurance training, this movement may require preventive strengthening exercises.

Aging of the human neuromuscular system

Loss of cells from the motor system occurs during the normal aging process, leading to reduction in the complement of motor neurons and muscle fibers. The latter age-related decrease in muscle mass has been termed "sarcopenia" and is often combined with the detrimental effects of a sedentary lifestyle in older adults, leading to a significant reduction in reserve capacity of the neuromuscular system, which is the primary subject of this review. Clear evidence of this aging effect is seen when voluntary or stimulated muscle strength is compared across the adult lifespan, with a steady decline of approximately 1-2% per year occurring after the sixth decade. Interestingly, when compared with isometric contractions, the effect of aging is more pronounced for concentric movements and less for eccentric movements (i.e., muscle shortening versus lengthening). This phenomenon appears to be linked to the stiffer muscle structures and prolonged myosin crossbridge cycles of aged muscles. It is encouraging that the capability of physiological adaptations in the motor pathways remains into very old age--when an appropriate exercise stimulus is given--and long-term prevention strategies are advocated to avoid excessive physical impairments and activity restrictions in this age group.