Age and sex-related decline of muscle strength across the adult lifespan: a scoping review of aggregated data.

Muscle strength is sex-related and declines with advancing age; yet, a comprehensive comparative evaluation of age-related strength loss in human females and males has not been undertaken. To do so, segmented piecewise regression analysis was performed on aggregated data from studies published from 1990 to 2018 and are available in CINAHL, EMBASE, MEDLINE, and PsycINFO databases. The search identified 5613 articles that were reviewed for physical assessment results stratified by sex and age. Maximal isometric and isokinetic 60°·s-1 knee extension (KE) and knee flexion (KF) contractions from 57 studies and 15 283 subjects (N = 7918 females) had sufficient data reported on females and males for meaningful statistical evaluation to be undertaken. The analysis revealed that isometric KE and KF strength undergo similar rapid declines in both sexes late in the sixth decade of life. Yet, there is an abrupt age-related decline in KE 60°·s-1 peak torque earlier in females (aged 41.8 years) than males (aged 66.7 years). In the assessment of KF peak torque, an age-related acceleration in strength loss was only identified in males (aged 49.3 years). The results suggest that age-related isometric strength loss is similar between sexes while the characteristics of KE and KF peak torque decline are sex-related, which likely explains the differential rate of age-related functional decline. Novelty Inclusion of muscle strength and torque of KE and KF data from >15 000 subjects. Isometric KE and KF strength loss are similar between sexes. Isokinetic 60°·s-1 KE torque decline accelerates 25 years earlier in females and female age-related KF peak torque decline does not accelerate with age.

Multi-Component Exercise with High-Intensity, Free-Weight, Functional Resistance Training in Pre-Frail Females: A Quasi-Experimental, Pilot Study.

BACKGROUND: No study has performed an exercise intervention that included high-intensity, free-weight, functional resistance training, and assessed frailty status as an inclusion criteria and outcome measure via original, standardized tools, in pre-frail females. OBJECTIVES: Determine if the intervention strategy is not only feasible and safe, but can also improve frailty status, functional task performance, and muscle strength. DESIGN: Pilot, quasi-experimental. SETTING: Community. PARTICIPANTS: 20 older-adults with pre-frailty characteristics. INTERVENTION: 12-weeks (3 days/week, 45-60 minutes/session) of multi-component exercise, inclusive of aerobic, resistance, balance and flexibility exercises. The crux of the program was balance and resistance exercises, the latter utilized high-intensity, free-weight, functional resistance training. The control group maintained their usual care. MEASUREMENTS: 1) Feasibility and safety (dropout, adherence, and adverse event); 2) Frailty (Frailty Phenotype, Clinical Frailty Scale, and gait speed); 3) Functional task performance (grip strength and sit-to-stand time); and 4) Isometric and isotonic strength of the knee extensors and elbow flexors. RESULTS: No participants dropped out of the intervention or experienced an adverse event, and adherence averaged 88.3%. The exercise group became less frail, whereas the control group became more frail. There was a significant within-group improvement in exercise participants gait speed (p ≤ 0.01, +0.24 m/sec), grip strength (p ≤ 0.01, +3.9 kg), and sit-to-stand time (p ≤ 0.01, -5.0 sec). There was a significant within-group improvement in exercise participants knee extension isometric torque (p ≤ 0.05, +7.4 Nm) and isotonic velocity (p = ≤ 0.01, +37.5 ˚/sec). Elbow flexion isotonic velocity significantly declined within the control group (p ≤ 0.01, -20.2 ˚/sec) and demonstrated a significant between-group difference (p ≤ 0.05, 40.73 ˚/sec) post-intervention. CONCLUSIONS: The intervention strategy appears to be feasible and safe, and may also improve frailty status, functional task performance, and muscle strength. These results help calculate effect size for a future randomized controlled trial.

Practical Implications for Strength and Conditioning of Older Pre-Frail Females.

Approaches to and benefits from resistance training for non-compromised older adults are well known. Less is understood about resistance training with pre-frail older adults, and even less information is available on the practical approaches to delivery. Herein, we describe an approach in pre-frail females who undertook a multi-component exercise intervention, inclusive of high-intensity, free-weight, functional resistance training. Capitalizing on the principle of overload is possible and safe for pre-frail females through constant reassurance of ability and adjustments in technique. Making exercise functionally relevant, for example, a squat is the ability to get on and off a toilet, resonates meaning. Older pre-frail females are affected by outside (clinical) influences. The exercise participant, and extraneous persons need to be educated on exercise approaches, to increase awareness, debunk myths, and enhance support for participation. Identification of individuality in a group session offers ability to navigate barriers for successful implementation.

Influence of biceps brachii tendon mechanical properties on elbow flexor force steadiness in young and old males.

Elbow flexor force steadiness (FS) depends on strength and decreases with age. Achilles tendon mechanics effect standing balance and isometric plantarflexion FS. This study investigated the influence of distal biceps brachii (BB) tendon mechanics and elbow flexor strength on age-related decline in FS. Nine young (23 ± 2 years) and nine old (77 ± 5 years) males performed submaximal isometric elbow flexion tasks at low (2.5%, 5%, 10% maximal voluntary contraction (MVC)) and high (20%, 40%, 60%, 80%MVC) forces in a neutral forearm position. Distal BB tendon elongation and cross-sectional area (CSA) were recorded on ultrasound to calculate mechanics of strain, stress, and stiffness. Coefficient of variation (CV) of force was used to assess relationship of FS to tendon mechanics and strength. Young were 22% stronger and 41% steadier than old (P < .05). Tendon stiffness (170.1 ± 132.9 N/mm; 113.0 ± 55.1 N/mm) did not differ with age (P > .05). Young had 40% less strain compared to old at 5% MVC, but 42% greater strain at 60% and 80% MVC (P ≤ .05). Stress was ~18% greater in young at 10%, 20%, and 80% MVC (P ≤ .05). At low forces, CV of force was predicted by stress (r2  = 0.56) in young, and stress and MVC (r2  = 0.641) in old. At high forces for both age groups, CV of force was predicted by MVC and stress (r2  = 0.39-0.43). Stress and strain is greater in young compared with old males. Because strength influences tendon mechanics and is also associated with FS, absolute strength is a large and modifiable contributor to age-related decline in FS.

Bilateral deficit in explosive force related to sit-to-stand performance in older postmenopausal women.

The purpose of this study was to determine whether the bilateral deficit (BLD) for maximal voluntary force (MVF) and rate of force development (RFD) influences sit-to-stand in older postmenopausal women. Fourteen women performed unilateral and bilateral maximal voluntary contractions during isometric leg-extension. The MVF and RFD over consecutive 50ms periods (0-50, 50-100 and 100-150ms) after force onset and the time to sit-to-stand test were calculated. There was only a BLD for RFD 0-50ms and 50-100ms. The time of sit-to-stand was moderately correlated to BLD for RFD 0-50ms (r=0.505; 95% CI: -0.035 to 0.817; P=0.06), but after controlling for physical activity level the relationship was stronger and statistically significant (r=0.605; 95% CI: 0.109 to 0.859; P=0.029). These results suggest that the BLD for explosive force (0-50ms) might represent a performance-limiting factor for sit-to-stand transfer in postmenopausal women and could be dependent of the physical activity level. Trial registered at Clinical Trials Gov.: NCT02434185.

Stretch training induces unequal adaptation in muscle fascicles and thickness in medial and lateral gastrocnemii.

This study compared adaptations in fascicle lengths, pennation angles, and muscle thickness of the lateral and medial gastrocnemii in response to 6 weeks of stretch training. The nondominant plantar flexors of 11 males were stretched five times per week for 6 weeks and compared with the contralateral leg and a nonstretched control group of 10 males. During stretch training, instantaneous electromyography was utilized to ensure passive muscle stretch. At baseline, week three, week six and 1 week after the conclusion of stretch training, ultrasound was used to measure fascicle lengths, pennation angles, muscle thickness of the lateral gastrocnemius and medial gastrocnemius, and Achilles tendon thickness and length. Plantar flexion torque was measured, and voluntary activation was assessed. Muscle thickness increased 5.6% after 6 weeks of stretch training (P=.009). The fascicles in the lateral gastrocnemius lengthened to a greater extent than the medial. Overall, fascicles lengthened 25% (P<.001) in the muscle tendon junction and 5.1% (P<.001) in the muscle belly. Pennation angles were unchanged in the medial gastrocnemius but decreased in the lateral gastrocnemius 7.1% (P=.02). There was no change in maximal voluntary contraction, voluntary activation, tendon length, or thickness. This study demonstrates that stretch training is a viable modality to alter muscle architecture of the human gastrocnemius through lengthening of muscle fascicles, decreasing pennation angles, and increasing muscle thickness, albeit adaptations are unequal between the lateral and medial heads.

Neuromuscular responses of the plantar flexors to whole-body vibration.

Enhanced physical performance following whole-body vibration (WBV) has been attributed to increased muscle activity; however, few studies have measured the mechanisms underlying these changes. The objective of this study was to measure the responsiveness of the Ia pathway as well as contractile properties in 16 young adults (24±2 years, eight men, eight women) following repeated bouts of acute WBV (45 Hz, 2 mm). Hoffman reflexes (H-reflex), compound muscle action potentials (M-wave), and twitch contractile properties were measured prior to and immediately following five 1-minute WBV exposures, and at 3, 5, 10, and 20 minute post-WBV. M-wave and H-reflex amplitudes decreased by 8% (P<.001) and by 46% (P<.05), respectively, whereas peak twitch torque decreased by 9% (P<.01) and rate of twitch torque development slowed 8% (P<.05). Percent voluntary activation and maximal plantar flexor torque were unchanged as a consequence of WBV (P>.05). In response to acute WBV, the root mean square of the soleus electromyography signal (EMGRMS ) increased by 8%, while the EMGRMS of the lateral gastrocnemius increased by 3% (P<.05). These data indicate that the responsiveness of the Ia pathway is diminished and contractile function is impaired immediately following WBV, and that the neural mechanisms underlying improved performance following WBV lie in alternative hypotheses possibly involving spindle disfacilitation or Golgi afferent modulation.

EMG Functional tasks recordings determines frailty phenotypes in males and females.

BACKGROUND: Identification of frailty is essential to understanding and mitigating age-related physical impairments. Previous studies have indicated that frailty phenotype can be identified through electromyography (EMG) when collected over the course of an 8-h day. However, long duration recordings challenge both the clinician and the older adults but activities of daily living that are most sensitive to changes in frailty status are currently unknown. The purpose of this study was to determine if muscle activity recorded during specific task, or groups of tasks, could be used to correctly classify middle-aged, non-frail, pre-frail, and frail older adult pheonotypes. METHODS: Fifteen middle-aged (49 ± 5 years) and 76 older adults (77 ± 8 years) participated. Older adults were categorized as non-frail (n = 49), pre-frail (n = 20), or frail (n = 7) using self-selected normal gait speed and a modified frailty index score. Bursts and gaps in EMG of the biceps brachii, triceps brachii, vastus lateralis, and biceps femoris were measured bilaterally during nine different functional tasks. RESULTS: Relatively high levels of success for frailty group classification (near 90%) can be achieved from EMG. Bursts were more frequent and gaps fewer in frail compared with middle-aged and non-frail adults. The numbers of gaps and muscle quiescence in the upper limbs were particularly important. Changes in muscle activity offer predictive value in identifying frailty phenotype. Completing functional tasks (rising from the floor, toilet and chair) while undergoing EMG assessment can contribute to the identification of differences in frailty phenotype among older adults.

Enhanced precision of ankle torque measure with an open-unit dynamometer mounted with a 3D force-torque sensor.

PURPOSE: Many studies have focused on maximum torque exerted by ankle joint muscles during plantar flexion. While strength parameters are typically measured with isokinetic or isolated ankle dynamometers, these devices often present substantial limitations for the measurement of torque because they account for force in only 1 dimension (1D), and the device often constrains the body in a position that augments torque through counter movements. The purposes of this study were to determine the contribution of body position to ankle plantar-flexion torque and to assess the use of 1D and 3D torque sensors. METHODS: A custom designed 'Booted, Open-Unit, Three dimension, Transportable, Ergometer' (B.O.T.T.E.) was used to quantify plantar flexion in two conditions: (1) when the participant was restrained within the unit (locked-unit) and (2) when the participant's position was independent of the ankle dynamometer (open-unit). Ten young males performed maximal voluntary isometric plantar-flexion contractions using the B.O.T.T.E. in open and locked-unit mechanical configurations. RESULTS: The B.O.T.T.E. was reliable with ICC higher than 0.90, and CV lower than 7 %. The plantar-flexion maximal resultant torque was significantly higher in the locked-unit compared with open-unit configuration (P < 0.001; +61 to +157 %) due to the addition of forces from the body being constrained within the testing device. A 1D compared with 3D torque sensor significantly underestimated the proper capacity of plantar-flexion torque production (P < 0.001; -37 to -60 %). CONCLUSIONS: Assessment of plantar-flexion torque should be performed with an open-unit dynamometer mounted with a 3D sensor that is exclusive of accessory muscles but inclusive of all ankle joint movements.

The effect of tendon vibration on motor unit activity, intermuscular coherence and force steadiness in the elbow flexors of males and females.

BACKGROUND: Compartmentalized responses in motor unit (MU) activity of the short head (SH) and long head (LH) of the biceps brachii are observed following forearm position change. Differential muscle spindle afferent distribution has been proposed as a potential mechanism underlying this behaviour. Tendon vibration is an effective, non-invasive method of increasing muscle spindle afferent activity of a target muscle group offering a paradigm in which this hypothesis may be investigated further. AIM: To determine the effect of tendon vibration on MU recruitment and discharge rates of the SH and LH, muscle activity of the elbow flexors and triceps brachii, intermuscular coherence among the SH, LH, brachioradialis and triceps brachii and force steadiness in young males and females during isometric elbow flexion. METHODS: Intramuscular electromyography (EMG) of the SH and LH, and surface EMG of the elbow flexors were recorded pre- and post-vibration during low-force isometric contractions. Motor unit recruitment thresholds, MU discharge rates and MU discharge variability; surface EMG amplitude, intermuscular coherence and force steadiness were determined pre- and post-vibration. RESULTS: Differential changes in all MU properties, EMG amplitude and intermuscular coherence were observed among elbow flexors. Although MU properties exhibited differential changes, they accounted for little variance in isometric force steadiness. However, intermuscular EMG coherence among all muscles investigated was reduced post-vibration. CONCLUSION: Uncoupling of common oscillatory input as a result of differential muscle spindle afferent inputs to elbow flexors may be responsible for the reduction in force steadiness following tendon vibration and a forearm position change.

How Do Community Physical and Occupational Therapists Classify Frailty? A pilot Study.

BACKGROUND: Frailty is a complex geriatric syndrome that is often difficult to diagnose, especially by healthcare professionals working in the community. Objectives, Measurements: This study examined how physical and occupational therapists classified community-dwelling clients using categories of 'nonfrail', 'prefrail' or 'frail' as compared to measurements of established frailty criteria from the Cardiovascular Health Study frailty index (CHSfi). RESULTS: Results indicate that community therapists underestimate frailty in comparison to the CHSfi. Therapists' classification of frailty suggested their perceptions of frailty may not only relate to client's functional capacity, but the context in which the client receives care. CONCLUSION: A multi-dimensional approach is required to capture all aspects of frailty across the healthcare continuum that accounts for how the client thrives within their personal environment.

Concurrence of Frailty and Parkinson's Disease.

BACKGROUND: Females with Parkinson's disease (PD) are at greater risk of frailty than males. Little is known about how age and disease-related characteristics influence frailty in females with PD because frailty studies often exclude persons with underlying neurological pathologies. OBJECTIVE: To determine age and disease-related characteristics that best explain physical frailty in community-dwelling females with and without PD. DESIGN AND MEASUREMENT: Correlation coefficients described relationships between PD-related characteristics and physical frailty phenotype criteria (Cardiovascular Health Study). Regression analysis identified associations between disease-related characteristics and frailty in non-PD and PD females. SETTING: Community-dwelling. PARTICIPANTS: Females with mild to moderate PD (n = 17, mean age = 66 ± 8.5 years) and non-PD (n = 18, mean age = 72 ± 13.2 years) participated. RESULTS: Daily carbidopa-levodopa dose best explained frailty in PD females (ß = 0.5), whereas in non-PD females, age (ß = 0.7) and comorbidity (ß = 0.5) were most associated with frailty. CONCLUSIONS: Dopaminergic medication explained frailty in PD and not measures of disease progression (i.e. severity, duration). In females without PD age-related accumulation of comorbidities resulted in greater risk of frailty. This indicates dopaminergic management of PD symptoms may better reflect frailty in females with PD than disease severity or duration. These data suggest the influence of underlying frailty should be considered when managing neurological conditions. Understanding how frailty concurrently exists with PD and how these conditions progress within the aging female will facilitate future care management.

Age- and sex-related differences for electromyography gaps during daily activity and a discrete task.

Temporal patterns of quiescent electromyography termed 'gaps' were investigated in young and old men and women for a discrete task and daily activity. Gaps in women (1.3±3.2) and old adults (1.5±3.4) were fewer compared with men (4.7±6.7) and young adults (4.6±6.9) for the discrete task (p<0.001). Gap duration was shorter for women (0.1±0.2s) and old adults (0.1±0.3s) compared with men (0.2±0.3s) and young adults (0.2±0.2s) (p<0.01). For daily activity, gap number was similar with age, but gap duration and percentage of total time occupied by gaps were less in old compared with young adults (50%), and in women compared with men (43%) (p<0.001). Results suggest gap activity is sensitive to type and duration of activity and that old adults and women demonstrate less quiescent electromyography than young adults and men.

Age independent and position-dependent alterations in motor unit activity of the biceps brachii.

In the biceps brachii, age-related differences in synaptic excitability and muscle architecture may affect motor unit (MU) activity differently depending on the position of the forearm. It was hypothesised that as a result of these age-related differences, greater changes in MU activity would accompany a change in forearm position in old when compared with young men. Six young (22 +/- 3 years) and six old (84 +/- 3 years) men maintained isometric elbow flexion at 10% of maximal voluntary contraction (MVC) during changes in forearm position. Forty-nine MUs in the short (SBB) and long (LBB) heads of the biceps brachii were followed. Motor unit recruitment and de-recruitment thresholds, motor unit discharge rates (MUDRs), and MU discharge variability were measured. Although an age-related decrease in MU recruitment thresholds, and increase in MU discharge variability was evident, changes in forearm position influenced MUDRs similarly in young and old men (P = 0.27). Motor unit recruitment thresholds of the SBB were highest in the pronated position (8.2 +/- 2.9 %MVC), whereas in the LBB they were highest in the supinated position (8.6 +/- 2.0 %MVC). Motor unit discharge rates of the LBB did not change with forearm position. In the SBB, MUDRs were highest when the forearm was supinated, and also greater when compared with the LBB in this position. No position-dependent changes were observed for MU discharge variability in the LBB, but the SBB exhibited greatest MU discharge variability in the pronated position. The results suggest that MU activity is modulated following a change in forearm position, but the response is similar in young and old adults.

Differential age-related changes in motor unit properties between elbow flexors and extensors.

AIM: Healthy adult ageing of the human neuromuscular system is comprised of changes that include atrophy, weakness and slowed movements with reduced spinal motor neurone output expressed by lower motor unit discharge rates (MUDRs). The latter observation has been obtained mostly from hand and lower limb muscles. The purpose was to determine the extent to which elbow flexor and extensor contractile properties, and MUDRs in six old (83 +/- 4 years) and six young (24 +/- 1 years) men were affected by age, and whether any adaptations were similar for both muscle groups. METHODS: Maximal isometric voluntary contraction (MVC), voluntary activation, twitch contractile properties, force-frequency relationship and MUDRs from sub-maximal to maximal intensities were assessed in the elbow flexors and extensors. RESULTS: Both flexor and extensor MVCs were significantly (P < 0.05) less (approximately 42% and approximately 46% respectively) in the old than in the young. Contractile speeds and the force-frequency relationship did not show any age-related differences (P > 0.05). For the elbow flexors contraction duration was approximately 139 ms and for the extensors it was approximately 127 ms for both age groups (P > 0.05). The mean MUDRs from 25% MVC to maximum were lower (approximately 10% to approximately 36%) in the old than in the young (P < 0.01). These age-related differences were larger for biceps (Cohen's d = 8.25) than triceps (Cohen's d = 4.79) brachii. CONCLUSION: Thus, at least for proximal upper limb muscles, mean maximal MUDR reductions with healthy adult ageing are muscle specific and not strongly related to contractile speed.

Age- and sex-related differences in muscle activation for a discrete functional task.

Electromyography (EMG) recordings for a typical 8-h day have indicated that burst activity is greater in old adults compared with young adults; these age-related adaptations might be due to the tasks undertaken. The purpose of the present study was to determine whether EMG burst activity differs between young and old men and women for a discrete task of daily living, and to assess whether the time of day when the task is performed influences the EMG burst patterns. Subjects completed a discrete functional task of a grocery bag carry prior to and following 8 h of daily activity. Surface EMG was recorded from the biceps brachii, triceps brachii, vastus lateralis, and biceps femoris. Spatial and temporal characteristics of the bursts were quantified as a period of EMG activity being greater than 2% maximum EMG and for a duration longer than 0.1 s. Burst activity did not differ between the morning and evening recordings, which indicate that the time of day does not influence burst activity recorded for a discrete task. Although there were no differences in burst number between young (10.9 +/- 1.0) and old (11.4 +/- 0.7) adults, burst duration and area were 3-7 times larger in old adults compared with young adults. The number of bursts in women (7.9 +/- 1.0) were ~85% less compared with men (14.6 +/- 0.7), but burst duration and burst area were approximately three times larger in women compared with men. Thus, older adults demonstrate higher levels of burst activity compared with young adults, and these age-related changes in burst activity are augmented in women.

The incidence of hematuria in middle distance track running.

The purpose of this study was to establish if middle distance track athletes experience hematuria during their competitive season interval workouts and, if so, what type of workout based on intensity and distance was most associated with hematuria. During a 4-week observational period, athletes (n = 10) underwent reagent strip urinalysis before and after their twice weekly interval sessions. Positive samples for hematuria were analyzed microscopically to accurately determine red blood cell (RBC) loss. Seventy-one individual interval workouts were observed, of which 32 cases of hematuria were reported. Nine cases of hematuria exhibited >100 RBC per High Power Field (Hpf). Furthermore, 90% of the athletes experienced post-workout hematuria at least once. The highest incidence of hematuria was observed after workouts run at 110% of VO(2peak) over short (600-1,500 m) to moderate (1,501-3,000 m) distances. All post-exercise cases of hematuria resolved within 2 hr of recovery.

Quadriceps muscle function and fatigue in women with Addison's disease.

In nine patients with Addison's disease (mean +/- SE: 51 +/- 2 years) receiving conventional steroid treatment, and nine age-matched healthy controls (56 +/- 2 years), we investigated maximum voluntary quadriceps force (MVC) and contractile properties evoked with stimulation and central activation both at rest and during a submaximal intermittent fatigue task. The MVC was similar (-3%), but twitch tension (-27%) and central activation were significantly less (-7%), and tetanic half-relaxation time was approximately 40% slower in the patients. Twitch amplitudes were potentiated by 6% in the patients, but unchanged in the control group. The patients self-terminated a submaximal intermittent fatigue protocol (0.6 duty cycle) at approximately 5 +/- 1 min, whereas the controls stopped when they lost 50% of MVC force ( approximately 10 +/- 1 min). Force loss was similar between groups over the first 5 min of the fatigue task. In the patient group, maximal and submaximal relative integrated electromyogram (IEMG) increased significantly in the first minute of fatigue and remained elevated, whereas the controls exhibited a gradual increase in submaximal IEMG with little change in maximal IEMG. These results indicate that conventionally treated Addison's patients have similar MVC strength, but altered contractile properties and decreased endurance compared with controls.

Neuromuscular properties and fatigue in older men following acute creatine supplementation.

The purpose of this study was to investigate the effects of creatine (Cr) supplementation in 12 older (65-82 years) men. The subjects were randomly assigned to a Cr or a placebo (P) group. Seven men were supplemented with 5 g of Cr and 5 g maltodextrin four times a day for 5 days (Cr), and 5 men consumed 5 g of maltodextrin four times a day for 5 days (P). Following this treatment body mass increased significantly in the Cr group (1 kg), but did not change in the P group, and measurements of arm anthropometry were not affected in either group. Prior to and following supplementation maximal isometric voluntary force (MVC), muscle activation, contractile properties and surface electromyography (EMG) were measured in the elbow flexor muscles at baseline, during a fatiguing task and over 10 min of recovery. The fatigue protocol involved both voluntary and contractile stimulated. Stimulated contractile properties, MVC, and muscle activation were not affected by Cr supplementation. Furthermore, there were no changes in time to fatigue, decline in MVC force, muscle activation, EMG or contractile properties during the fatigue protocol. The rates of recovery of voluntary force, and stimulated contractile force did not change following Cr supplementation. These results indicate that short-term Cr supplementation in older men does not influence isometric performance of the elbow flexor muscles.

Bilateral and unilateral contractions: possible differences in maximal voluntary force.

The issue of whether there is a difference in the amount of force produced from a simultaneous two-limb maximal contraction compared to the sum of individual one-limb contractions has received considerable debate in the literature. A bilateral deficit (BLD) is when the resultant force from bilateral homonymous limb contractions is less than the summed force of individual limb contractions. Determining whether differences exist between one- and two-limb movements may provide insight into complex neuromuscular control patterns. Many dynamic two-limb studies report a BLD, whereas isometric studies are more numerous and controversial. It is important to categorize the movements studied in order to establish consistency. This paper purports that the BLD is an unstable phenomenon, and its presence should be considered in the context of the movement studied. Most likely, this phenomenon is dependent upon some minor deviation in descending drive between the cortical level and peripheral motor neuron