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 methods
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.

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Progressive resistance strength training for improving physical function in older adults

1. The mechanical power spent to accelerate the limbs relative to the trunk in level walking and running, W(int), has been measured at various ;constant' speeds (3-33 km/hr) with the cinematographic procedure used by Fenn (1930a) at high speeds of running.2. W(int) increases approximately as the square of the speed of walking and running. For a given speed W(int) is greater in walking than in running.3. In walking above 3 km/hr, W(int) is greater than the power spent to accelerate and lift the centre of mass of the body at each step, W(ext) (measured by Cavagna, Thys & Zamboni, 1976b). In running W(int) W(ext).4. The total work done by the muscles was calculated as W(tot) = W(int) + W(ext). Except that at the highest speeds of walking, the total work done per unit distance W(tot)/km is greater in running than in walking.5. The efficiency of positive work was measured from the ratio W(tot)/Net energy expenditure: this is greater than 0.25 indicating that both in walking and in running the muscles utilize, during shortening, some energy stored during a previous phase of negative work (stretching).6. In walking the efficiency reaches a maximum (0.35-0.40) at intermediate speeds, as may be expected from the properties of the contractile component of muscle. In running the efficiency increases steadily with speed (from 0.45 to 0.70-0.80) suggesting that positive work derives mainly from the passive recoil of muscle elastic elements and to a lesser extent from the active shortening of the contractile machinery. These findings are consistent with the different mechanics of the two exercises.

https://physoc.onlinelibrary.wiley.com/doi/pdf/10.1113/jphysiol.1977.sp011866

Mechanical work and efficiency in level walking and running

Upright standing and walking tasks require the integration of several sources of sensory information In a normal and highly predictable environment, locomotor synergies involving several muscles may take place at lower spinal levels with neural circuitry tuned by local loops of assistance or self-organizing processes generated in coordinative networks When ongoing regulation of gait is necessary (obstacles, changes in direction) supraspinal involvement is necessary to perform movements adapted to the environment Using a classical information processing framework and a dual-task methodology, it is possible to evaluate the attentional demands for performing static and dynamic equilibrium tasks The present experiment evaluates whether the attentional requirements for a control sitting condition and for standing and walking conditions vary with the intrinsic balance demands of the tasks The results show that standing and walking conditions required more attention than sitting in a chair The attentional cost for walking was also significantly greater than for standing For the walking task, reaction times when subjects were in singlesupport phase (small base of support) were significantly longer than those in double-support phase, suggesting that the attentional demands increased with an increase in the balance requirements of the task Balance control requires a continuous regulation and integration of sensory inputs; increasing balance demands loads the higher level cognitive system

Attentional demands for static and dynamic equilibrium

Muscle strength and, to a greater extent, power inexorably decline with ageing. Quantitative loss of muscle mass, referred to as “sarcopenia”, is the most important factor underlying this phenomenon. However, qualitative changes of muscle fibres and tendons, such as selective atrophy of fast-twitch fibres and reduced tendon stiffness, and neural changes, such as lower activation of the agonist muscles and higher coactivation of the antagonist muscles, also account for the age-related decline in muscle function. The selective atrophy of fast-twitch fibres has been ascribed to the progressive loss of motoneurons in the spinal cord with initial denervation of fast-twitch fibres, which is often accompanied by reinnervation of these fibres by axonal sprouting from adjacent slow-twitch motor units (MUs). In addition, single fibres of older muscles containing myosin heavy chains of both type I and II show lower tension and shortening velocity with respect to the fibres of young muscles. Changes in central activation capacity are still controversial. At the peripheral level, the rate of decline in parameters of the surface-electromyogram power spectrum and in the action-potential conduction velocity has been shown to be lower in older muscle. Therefore, the older muscle seems to be more resistant to isometric fatigue (fatigue-paradox), which can be ascribed to the selective atrophy of fast-twitch fibres, slowing in the contractile properties and lower MU firing rates. Finally, specific training programmes can dramatically improve the muscle strength, power and functional abilities of older individuals, which will be examined in the second part of this review.

Muscle strength, power and adaptations to resistance training in older people

Background. The aim of this systematic review was to quantify the effectiveness of progressive resistance strength training (PRT) to reduce physical disability in older people. Methods. Randomized controlled trials were identified from searches of relevant databases and study reference lists and contacts with researchers. Two reviewers independently screened the trials for eligibility, rated their quality, and extracted data. Only randomized controlled trials utilizing PRT as the primary intervention in participants, whose group mean age was 60 years or older, were included. Data were pooled using fixed or random effect models to produce weighted mean differences (WMD) and 95% confidence intervals (CI). Standardized mean differences (SMD) were calculated when different units of measurement were used for the outcome of interest. Results. 62 trials (n ¼ 3674) compared PRT with a control group. 14 trials had data available to allow pooling of disability outcomes. Most trials were of poor quality. PRT showed a strong positive effect on strength, although there was significant heterogeneity (41 trials [n ¼1955], SMD 0.68; 95% confidence interval [CI] 0.52, 0.84). A modest effect was found on some measures of functional limitations such as gait speed (14 trials [n ¼ 798], WMD 0.07 meters per second; 95% CI 0.04, 0.09). No evidence of an effect was found for physical disability (10 trials [n ¼ 722], SMD 0.01; 95% CI � 0.14, 0.16). Adverse events were poorly investigated, but occurred in most studies where they were defined and prospectively monitored. Conclusions. PRT results in improvements to muscle strength and some aspects of functional limitation, such as gait speed, in older adults. However, based on current data, the effect of PRT on physical disability remains unclear. Further, due to the poor reporting of adverse events in trials, it is difficult to evaluate the risks associated with PRT.

Systematic Review of Progressive Resistance Strength Training in Older Adults

The interplay of muscular and external forces in human ambulation.

Introduction: In this study we tested the hypothe- sis that caffeine supplementation improves neuromuscular func- tion, which has both nutritional and clinical relevance. Methods: Fourteen male subjects (mean 6 SD: 23.8 6 2.8 years) volun- teered in a double-blind, repeated-measures study with placebo (PLA) or caffeine (CAFF) (6 mg kg � 1 ). Maximal voluntary iso- metric contractions (MVCs), evoked maximal twitch, and maxi- mal isokinetic contractions during elbow flexion were assessed. Mechanical and electromyographic (EMG) signals from the biceps brachii muscle were recorded, and muscle fiber conduc- tion velocity (CV) was calculated to evaluate changes in the muscle force-velocity relationship and muscle fiber recruitment. Results: The torque-angular velocity curve was enhanced after CAFF supplementation. This was supported by a concomitant increase of CV values (8.7% higher in CAFF). Conclusions: Caffeine improves muscle performance during short-duration maximal dynamic contractions. The concomitant improvement of mean fiber CV supports the hypothesis of an effect of caf- feine on motor unit recruitment. Muscle Nerve 000: 000-000, 2011

Caffeine improves neuromuscular function during maximal dynamic exercise.

Evaluation of the compressive load acting on the lumbar spine (L3-L4) during half-squat exercises executed with a barbell resting on the subject's shoulders was undertaken. The kinematics of the upper body segments of two male and two female subjects as well as the barbell were described using data obtained by means of an optoelectronic system (CoSTEL). L3-L4 compressive load was calculated using a model of the anatomy of the trunk musculoskeletal system. Filtered surface electromyographic trunk flexor recordings from the obliquus externus and rectus abdominis and trunk extensor erectores spinae muscles as well as measurement of the ground reaction forces were also carried out for predicted result validation. During half-squat exercises with barbell loads in the range 0.8 to 1.6 times body weight the compressive loads on the L3-L4 segment vary between 6 and 10 times body weight. Erectores spinae contraction force was predicted to be between 30 and 50% of the relevant maximal isometric force. The magnitude of trunk flexion was found to be the variable which influenced most spinal compression load.

Lumbar spine loading during half-squat exercises.

This paper aimed at investigating the neuromuscular response of knee flexor and extensor muscles in elite karateka and karate amateurs (Amateurs) during isokinetic knee flexion/extensions and during the execution of a front kick (FK). Surface electromyograms (sEMG) were recorded from the right vastus lateralis (VL) and biceps femoris (BF) muscles with a four-array electrode during maximal isometric knee flexion and extension (maximal voluntary contraction), during isokinetic contractions (30 degrees , 90 degrees , 180 degrees , 270 degrees , 340 degrees , 400 degrees /s), and during the FK. The level of VL and BF agonist (ago) and antagonist (ant) activation during the isokinetic and FK protocols was quantified through normalized sEMG root mean square value (%RMS(ago/ant-ISOK/FK)). VL and BF average muscle fiber conduction velocity (CV) was computed for isokinetic and FK. Isokinetic flexion and extension torques and knee angular velocity during FK were also assessed. Analysis of variance was used to test the effect of group, angular velocity, and task on the assessed variables (P < 0.05). Elite karateka showed higher isokinetic knee flexion torque when compared with Amateurs. For all angular velocities, VL and BF %RMS(ant-isokinetic) were lower in elite karateka, while their BF-CV(isokinetic) BF-CV(front kick) and BF %RMS(ant-front kick) values were higher. For VL and BF, %RMS(ago-front kick) was lower than %RMS(ago-isokinetic) in both groups. Elite karateka demonstrated a typical neuromuscular activation strategy that seems task and skill level dependent. Knee flexion torque and CV results suggest the presence of an improved ability of elite karateka to recruit fast MUs as a part of training induced neuromuscular adaptation.

Neuromuscular control adaptations in elite athletes: the case of top level karateka.

The present study was carried out in order to quantify the athlete's endurance impairment after two out of three sequential events of Olympic Triathlon (OT). Furthermore the significance of ventilatory threshold (Tvent) and peak of oxygen uptake (VO 2 peak) as triathlete's performance predictors was assessed. Tvent and VO 2 peak were measured in six male triathletes performing an incremental treadmill test a week before an AD HOC triathlon event. The same test was applied immediately after the first two segments of the triathlon (1.5 km swim, 32 km bike). VO 2 peak and Tvent measured during the latter test were reduced compared to the first test. VO 2 peak decreased from 69 to 64 ml · kg -1 · min1' and Tvent from 58 to 51 ml · kg -1 · min -1 (p<0,01), respectively. VO 2 peak and Tvent measured in the first test were well correlated (P<0.05) to both running and cycling times. The Tvent measured during the second test was related to the running time but with a higher significance (p < 0.01) than in the first test. The impairment in the endurance performance induced by the first two segments of OT is an important aspect to consider both in training and in race strategy. These results also provide evidence that VO 2 peak and Tvent are good predictors of triathlon performance at least in cycling and running events.

F. Figura

Papers

The interplay of muscular and external forces in human ambulation.

Caffeine improves neuromuscular function during maximal dynamic exercise.

Lumbar spine loading during half-squat exercises.

Neuromuscular control adaptations in elite athletes: the case of top level karateka.

Decrease of endurance performance during Olympic Triathlon.