Triceps surae muscle power, volume, and quality in older versus younger healthy men

Effects of Eccentric Phase Velocity on Bench Press Concentric Bar Velocity in the Young and Elderly

This study aimed to investigate the impact of bar velocity during the eccentric phase on subsequent concentric performance in the young and elderly. Twelve elderly women (65.2+4.2 years) and 16 young women (23.1+2.1 years) were randomly assigned to four experimental conditions that combined high-velocity eccentric actions (HVECC; maximum velocity) and moderate-velocity eccentric actions (MVECC; 2.0 s), using 30% and 60% of their 1-repetition maximum (1RM) on the Smith machine bench press. Measurements of mean propulsive velocity (MPV), peak velocity (PV), and mean power (MP) were recorded. Two-way ANOVA with repeated measures was applied for each variable, when needed, the Bonferroni post hoc was used. Statistical significance was set at p<0.05, and effect size (ES) was established by Cohen's d z. The results demonstrated that elderly women showed improved performance in MPV (+10.0%; ES=- 0.58; p=0.009) and MP (+11.7%; ES=- 0.14; p=0.045) when utilizing HVECC at 30% 1RM only. Moreover, young women exhibited superior performance for both 30% and 60% 1RM when using HVECC for all variables analyzed (p<0.05). The HVECC appears to have an impact on the subsequent performance of the concentric phase, particularly when lighter loads (30% 1RM) are utilized, regardless of the age group.

Sedentary behaviour (especially accumulation pattern) has an independent negative impact on skeletal muscle size and architecture in community-dwelling older adults

Prolonged sedentary behaviour (SB) i.e. longer bouts, is suggested to have a range of negative health effects, independent of habitual light and medium-to-vigorous physical activity (LIPA or MVPA). Any effect on musculoskeletal size, architecture or morphology has seldom been reported in older adults. Moreover, no study has yet determined if any association would persist following adjustment for covariates. Therefore, the aim of the present study was to investigate the associations between SB, and properties of the Gastrocnemius Medialis (GM) muscle, in a cross-sectional sample of older adults using compositional data analysis. 105 healthy older adults (73±6y) wore a thigh mounted tri-axial accelerometer for seven consecutive days, and underwent ultrasound [e.g. muscle length (Lm), anatomical cross-sectional area (ACSA), muscle volume (VM), fascicle length (LF), & physiological cross-sectional area (PCSA)], body composition (e.g. DEXA) and health (e.g. medical history) assessments. In-unadjusted models, SB time was negatively associated with ACSA at 75% of Lm (R2adj = 0.085), VM (R2adj = 0.020), and PCSA (R2adj = 0.039). Standing was positively associated with pennation angle (R2adj = 0.110), which persisted following co-variate adjustment (R2adj = 0.296). In fully adjusted models, both SB & LIPA time were associated with ACSA at 75% of Lm (Both R2adj = 0.393). Standing and light activity time were also associated with LF, VM, & PCSA (R2adj 0.116-0.573). In fully adjusted models, SB pattern parameters (i.e. the manner in which sedentary behaviour is accumulated daily throughout waking hours such as the timing, duration and frequency of sedentary bouts), were associated with GM muscle properties (R2adj 0.156-0.564) including LM, LF, and VM. The pattern, rather than accumulated daily SB time, was associated with the size and architecture of the GM. Our results suggest that regardless of co-existing habitual physical activities, SB bouts should be kept short and frequently interrupted to offset some of the deleterious ageing-related muscle architecture characteristics changes.

Human skeletal muscle-specific atrophy with aging: a comprehensive review

Age-related skeletal muscle atrophy appears to be a muscle group-specific process, yet only a few specific muscles have been investigated and our understanding in this area is limited. This review provides a comprehensive summary of the available information on age-related skeletal muscle atrophy in a muscle-specific manner, nearly half of which comes from the quadriceps. Decline in muscle-specific size over ∼50 yr of aging was determined from 47 cross-sectional studies of 982 young (∼25 yr) and 1,003 old (∼75 yr) individuals and nine muscle groups: elbow extensors (-20%, -0.39%/yr), elbow flexors (-19%, -0.38%/yr), paraspinals (-24%, -0.47%/yr), psoas (-29%, -0.58%/yr), hip adductors (-13%, -0.27%/yr), hamstrings (-19%, -0.39%/yr), quadriceps (-27%, -0.53%/yr), dorsiflexors (-9%, -0.19%/yr), and triceps surae (-14%, -0.28%/yr). Muscle-specific atrophy rate was also determined for each of the subcomponent muscles in the hamstrings, quadriceps, and triceps surae. Of all the muscles included in this review, there was more than a fivefold difference between the least (-6%, -0.13%/yr, soleus) to the most (-33%, -0.66%/yr, rectus femoris) atrophying muscles. Muscle activity level, muscle fiber type, sex, and timeline of the aging process all appeared to have some influence on muscle-specific atrophy. Given the large range of muscle-specific atrophy and the large number of muscles that have not been investigated, more muscle-specific information could expand our understanding of functional deficits that develop with aging and help guide muscle-specific interventions to improve the quality of life of aging women and men.

Age-related performance fatigability: a comprehensive review of dynamic tasks

Adult ageing is associated with a myriad of changes within the neuromuscular system, leading to reductions in contractile function of old adults. One of the consequences of these age-related neuromuscular adaptations is altered performance fatigability, which can limit the ability of old adults to perform activities of daily living. Whereas age-related fatigability of isometric tasks has been well characterized, considerably less is known about fatigability of old adults during dynamic tasks involving movement about a joint, which provides a more functionally relevant task compared to static contractions. This review provides a comprehensive summary of age-related fatigability in dynamic contractions, where the importance of task specificity is highlighted with a brief discussion of the potential mechanisms responsible for differences in fatigability between young and old adults. The angular velocity of the task is critical for evaluating age-related fatigability, as tasks which constrain angular velocity (i.e., isokinetic) produce equivocal age-related differences in fatigability, whereas tasks involving unconstrained velocity (i.e., isotonic-like) consistently induce greater fatigability of old compared to young adults. These unconstrained velocity tasks, that are more closely associated with natural movements, offer an excellent model to uncover the underlying age-related mechanisms of increased fatigability. Future work evaluating the mechanisms of increased age-related fatigability of dynamic tasks should be evaluated using task-specific contractions (i.e., dynamic), particularly for assessment of spinal and supra-spinal components. Advancing our understanding of age-related fatigability is likely to yield novel insights and approaches for improving mobility limitations in old adults.

Muscle quality indices separately associate with joint-level power-related measures of the knee extensors in older males

PURPOSE

The purpose of this study was to investigate associations of muscle quality indices with joint-level power-related measures in the knee extensors of thirty-two older males (65-88 years).

METHODS

Muscle quality indices included: echo intensity, ratio of intracellular- to total water content (ICW/TW), and specific muscle strength. Echo intensity was acquired from the rectus femoris (EI_RF) and vastus lateralis (EI_VL) by ultrasonography. ICW/TW was computed from electrical resistance of the right thigh obtained by bioelectrical impedance spectroscopy. Specific muscle strength was determined as the normalized maximal voluntary isometric knee extension (MVIC) torque to estimated knee extensor volume. Isotonic maximal effort knee extensions with a load set to 20% MVIC torque were performed to obtain the knee extension power-related measures (peak power, rate of power development [RPD], and rate of velocity development [RVD]). Power and RPD were normalized to MVIC.

RESULTS

There were no significant correlations between muscle quality indices except between EI_RF and EI_VL (|r|≤ 0.253, P ≥ 0.162). EI_RF was negatively correlated with normalized RPD and RVD (r ≤  - 0.361, P ≤ 0.050). ICW/TW was positively correlated with normalized peak power (r = 0.421, P = 0.020). Specific muscle strength was positively correlated with absolute peak power and RPD (r ≥ 0.452, P ≤ 0.012).

CONCLUSION

Knee extension power-related measures were lower in participants with higher EI, lower ICW/TW, and lower specific muscle strength, but the muscle quality indices may be determined by independent physiological characteristics.

Human skeletal muscle size with ultrasound imaging: a comprehensive review

Skeletal muscle size is an important factor in assessing adaptation to exercise training and detraining, athletic performance, age-associated atrophy and mobility decline, clinical conditions associated with cachexia, and overall skeletal muscle health. Magnetic resonance (MR) imaging and computed tomography (CT) are widely accepted as the gold standard methods for skeletal muscle size quantification. However, it is not always feasible to use these methods (e.g., field studies, bedside studies, large cohort studies). Ultrasound has been available for skeletal muscle examination for more than 50 years and the development, utility, and validity of ultrasound imaging are underappreciated. It is now possible to use ultrasound in situations where MR and CT imaging are not suitable. This review provides a comprehensive summary of ultrasound imaging and human skeletal muscle size assessment. Since the first study in 1968, more than 600 articles have used ultrasound to examine the cross-sectional area and/or volume of 107 different skeletal muscles in more than 27,500 subjects of various ages, health status, and fitness conditions. Data from these studies, supported by decades of technological developments, collectively show that ultrasonography is a valid tool for skeletal muscle size quantification. Considering the wide-ranging connections between human health and function and skeletal muscle mass, the utility of ultrasound imaging will allow it to be employed in research investigations and clinical practice in ways not previously appreciated or considered.

Prefrontal Cortical Activity During Preferred and Fast Walking in Young and Older Adults: An fNIRS Study

Age-related changes may affect the performance during fast walking speed. Although, several studies have been focused on the contribution of the prefrontal cortex (PFC) during challenging walking tasks, the neural mechanism underling fast walking speed in older people remain poorly understood. Therefore, the aim of this study was to investigate the influence of aging on PFC activity during overground walking at preferred and fast speeds. Twenty-five older adults (67.37 ± 5.31 years) and 24 young adults (22.70 ± 1.30 years) walked overground in two conditions: preferred speed and fast walking speed. Five trials were performed for each condition. A wireless functional near-infrared spectroscopy (fNIRS) system measured PFC activity. Gait parameters were evaluated using the GAITRite system. Overall, older adults presented higher PFC activity than young adults in both conditions. Speed-related change in PFC activity was observed for older adults, but not for young adults. Older adults significantly increased activity in the left PFC from the preferred to fast walking condition whereas young adults had similar levels of PFC activity across conditions. Our findings suggest that older adults need to recruit additional prefrontal cognitive resources to control walking, indicating a compensatory mechanism. In addition, left PFC seems to be involved in the modulation of gait speed in older adults.

Ankle joint rotation and exerted moment during plantarflexion dependents on measuring- and fixation method

We examined the effect of ankle joint fixation vs increased foot pressure (aiming to reduce dynamometer-subject elasticity (DSE)) on the exerted moment during plantarflexion contraction. We also examined the joint rotation in dependence of the measuring site (forefoot, rearfoot) and the foot condition (fixed, free). We hypothesized higher exerted moments due to reduced DSE compared to fixed condition and an effect of fixation on the joint rotation in dependence of the measuring site. Fourteen healthy individuals (28.7±6.9y) completed in randomized order maximal isometric plantarflexions in four different positions (0-3-6-9 cm) and two ankle joint conditions (fixed-free). Kinematics of the rear- and forefoot were obtained synchronously. We found higher moment in the fixed compared to the free condition at all positions. The maximum moment in the fixed condition did not differ at any position. At the fixed condition, the forefoot rotation did not differ at any position (~5°) while at free condition we observed a significant rotation reduction (form ~12 to ~5°). The rearfoot rotation did not differ between conditions at any position while a significant joint angle reduction was observed (~10 to ~6° and ~12 to ~6°; fixed-free respectively). The results indicate that with appropriate foot fixation the maximum moment can be achieved irrespective of the position. With the foot secured, the measuring site influences the rotational outcome. We suggest that for a minimization of the joint rotation a fixation and the forefoot-measuring site should be preferred. Additionally, for unconstrained foot kinematic observations both measuring sites can be obtained.

Effects of Self-Selected Step Length and Trunk Position on Joint Kinetics in Highly Physically Fit Older Adults

The causes of age-related differences in lower-extremity joint moments and powers are unknown. The purpose of this study was to determine the effects of highly physically active older adults walking with (1) a step length similar to young adults and (2) an upright trunk posture, on hip and ankle joint kinetics. The authors hypothesized that, compared with their self-selected walking mechanics, older adults would exhibit decreased hip kinetics and increased ankle kinetics when prescribed a young adult step length, and would exhibit decreased hip extension moments when maintaining an upright trunk posture during walking. A total of 12 active older adults (67 [5] y) and 13 active young adults (21 [3] y) walked at 1.3 m/s. The older adults also walked at 1.3 m/s with step lengths prescribed from height-matched young adults and, in a separate condition, walked with an upright trunk. The older adults did not display larger ankle kinetics or smaller hip kinetics in either condition compared to walking with a self-selected step length. These findings indicate that step length and trunk position do not primarily contribute to age-related differences in kinetics in highly active older adults and should serve as a starting point for investigating alternative explanations.

Skeletal muscle size, function, and adiposity with lifelong aerobic exercise

We examined the influence of lifelong aerobic exercise on skeletal muscle size, function, and adiposity. Young exercisers [YE; n = 20, 10 women (W), 25 ± 1 yr], lifelong exercisers (LLE; n = 28, 7 W, 74 ± 2 yr), and old healthy nonexercisers (OH; n = 20, 10 W, 75 ± 1 yr) were studied. On average, LLE exercised 5 days/wk for 7 h/wk over the past 52 ± 1 yr. The LLE men were subdivided by exercise intensity [Performance (LLE-P), n = 14; Fitness (LLE-F), n = 7]. Upper and lower leg muscle size and adiposity [intermuscular adipose tissue (IMAT)] were determined via MRI, and quadriceps isotonic and isometric function was assessed. For the quadriceps, aging decreased muscle size, isotonic and isometric strength, contraction velocity (men only), and power (P < 0.05). In women, LLE did not influence muscle size or function. In men, LLE attenuated the decline in muscle size and isometric strength by ~50% (P < 0.05). LLE did not influence other aspects of muscle function, nor did training intensity influence muscle size or function. For the triceps surae, aging decreased muscle size only in the women, whereas LLE (both sexes) and training intensity (LLE men) did not influence muscle size. In both sexes, aging increased thigh and calf IMAT by ~130% (P < 0.05), whereas LLE attenuated the thigh increase by ~50% (P < 0.05). In the LLE men, higher training intensity decreased thigh and calf IMAT by ~30% (P < 0.05). In summary, aging and lifelong aerobic exercise influenced muscle size, function, and adipose tissue infiltration in a sex- and muscle-specific fashion. Higher training intensity throughout the life span provided greater protection against adipose tissue infiltration into muscle.NEW & NOTEWORTHY This is the first study to examine skeletal muscle size, function, and adiposity in women and men in their eighth decade of life that have engaged in lifelong aerobic exercise. The findings reveal sex and upper and lower leg muscle group-specific benefits related to skeletal muscle size, function, and adiposity and that exercise intensity influences intermuscular adiposity. This emerging cohort will further our understanding of the health implications of maintaining exercise throughout the life span.

Simplified Triceps Surae Muscle Volume Assessment in Older Adults

Triceps surae (TS) muscle volume can be estimated in young adults by only considering the maximal anatomical cross-sectional area (ACSA_max) and the length of the muscle due to the presence of a constant muscle-specific shape factor. This study aimed to investigate if this simplified muscle volume assessment is also applicable in older adults or if muscle-specific shape changes with aging. MRI sequences were taken from the dominant leg of 21 older female adults. The boundaries of all three TS muscles (SOL, soleus; GM, gastrocnemius medialis; GL, gastrocnemius lateralis) were manually outlined in transverse image sequences, and muscle volume for each muscle was calculated as the integral of the obtained cross-sectional areas of the contours along the whole length of the muscle (measured volume) and, in addition, by using the average muscle-specific shape factors of each muscle obtained from the ratio of the measured volume and the product of ACSA_max and the muscle length (estimated volume). There were no differences in the measured and estimated muscle volumes (SOL: 357.7 ± 61.8 vs. 358.8 ± 65.3 cm³; GM: 179.5 ± 32.8 vs. 179.8 ± 33.3 cm³; GL: 90.2 ± 15.9 vs. 90.4 ± 14.8 cm³). However, when using the reported shape factors of younger adults instead, we found a significant (p < 0.05) overestimation of muscle volume for SOL and GM with average RMS differences of 6.1 and 7.6%, respectively. These results indicate that corrections of muscle-specific shape factors are needed when using the previously proposed simplified muscle volume assessment as aging may not only be accompanied with muscle atrophy but also changes in the shape of skeletal muscle.

Neuromuscular function of the plantar flexors and predictors of peak power in middle-aged and older males

Little evidence exists regarding the contribution of torque and velocity to the age-related decrease in peak power (PP) for the plantar flexors (PFs). A comprehensive assessment of PF neuromuscular function is necessary to elucidate age-related changes, especially between middle-aged and older adults, in order to identify early, age-related decrements. Thus, the purpose of this study was to examine neuromuscular function of the PFs in middle-aged and older males, and identify predictors of PP. Twenty-eight healthy, middle-aged (n = 13; 45.1 ± 2.7 yrs) and older (n = 15; 65.3 ± 3.2 yrs) males performed concentric isotonic PF contractions ranging in intensity from 20% to 70% isometric strength using a dynamometer. PP in addition to velocity and torque at the moment in time PP occurred, as well as the rate of velocity, torque (RTD), and power (RPD) development were recorded. The rate of electromyography rise (RER) was derived from the linear slope of the normalized electromyography signal. Isometric and concentric dynamic strength were assessed, as well as cross-sectional area and muscle quality (i.e., echo intensity) of the PFs via panoramic ultrasonography. The relationship between serum c-terminal agrin levels and select variables was examined to explore the potential role of neuromuscular junction deterioration. Appendicular lean mass and physical activity level were similar between groups (p > 0.05), and only PP (p = 0.046; d = 0.79), RPD (p = 0.026; d = 0.90), RTD (p = 0.022; d = 0.91), and RER (p = 0.010; d = 1.04) were lower in older males. When groups were collapsed, RTD was the only significant predictor of PP, while c-terminal agrin levels were not associated with any variables. Our findings indicate that PP and time-dependent parameters of muscle activation and contractile function of the PFs are dramatically diminished in older adults compared to middle-aged adults. PP is produced at the same velocity and relative intensity in middle-aged and older males, and RTD is most influential for PP. The inability of the PFs to be rapidly activated appeared to be influential for the age-related impairment in PP and time-dependent contractile parameters.

Anterior subject positioning affects the maximal exerted isometric plantar flexion moment

We examined the effect of increased anterior subject positioning toward the dynamometer's footplate during maximal voluntary isometric contractions (MVCs) on the joint moment, rotation and rate of torque development (RTD). Fourteen subjects, with their hip flexed (110°) and knee fully extended (180°), underwent ramp maximal and rapid voluntary isometric plantar flexion contractions at 4 different positions (0, 3, 6 and 8 cm; randomized). At position "0 cm", the foot was in full contact with the footplate; at the additional positions, the chair was moved forward. Body kinematics (VICON) and kinetics (HUMAC Norm, PEDAR) were captured synchronously during MVCs and RTDs. The results showed that the maximal exerted joint moment was significantly (p<0.01) increased by >32% from the 0-cm to 8-cm position (126 and 172 Nm, respectively); however, at the "6 cm" and "8 cm" positions, no significant difference was found. The joint rotation was significantly (p<0.01) reduced by >50% (from 15.5 to 7.1°; 0-8 cm). The maxRTD was only significantly higher at "6 cm" compared with the "0 cm" position. The time to reach maxRTD showed shorter tendencies for the "8 cm" position than for all other positions. The results indicate an underestimation of the plantar flexor maximal force potential with the current measuring technique. This could be critical in pre-post study designs where a 2-cm alteration in the chair position can induce an error of ~9% in the joint moment. The joint rotation could be reduced but not completely eliminated. For position standardization purposes, a pressure >220 kPa under the subject's foot is needed to achieve the maximal joint moment. We discussed the possible origins (fascicle length, neural drive) of the increased joint moment.

Matching Participants for Triceps Surae Muscle Strength and Tendon Stiffness Does Not Eliminate Age-Related Differences in Mechanical Power Output During Jumping

Reductions in muscular power output and performance during multi-joint motor tasks with aging have often been associated with muscle weakness. This study aimed to examine if matching younger and middle-aged adults for triceps surae (TS) muscle strength and tendon stiffness eliminates age-related differences in muscular power production during drop jump. The maximal ankle plantar flexion moment and gastrocnemius medialis tendon stiffness of 29 middle-aged (40-67 years) and 26 younger (18-30 years) healthy physically active male adults were assessed during isometric voluntary ankle plantar flexion contractions using simultaneous dynamometry and ultrasonography. The elongation of the tendon during the loading phase was assessed by digitizing the myotendinous junction of the gastrocnemius medialis muscle. Eight younger (23 ± 3 years) and eight middle-aged (54 ± 7 years) adults from the larger subject pool were matched for TS muscle strength and tendon stiffness (plantar flexion moment young: 3.1 ± 0.4 Nm/kg; middle-aged: 3.2 ± 0.5 Nm/kg; tendon stiffness: 553 ± 97 vs. 572 ± 100 N/mm) and then performed series of drop jumps from different box heights (13, 23, 33, and 39 cm) onto a force plate (sampling frequency 1000 Hz). The matched young and middle-aged adults showed similar drop jump heights for all conditions (from lowest to highest box height: 18.0 ± 3.7 vs. 19.7 ± 4.8 cm; 22.6 ± 4.2 vs. 22.9 ± 4.9 cm; 24.8 ± 3.8 vs. 23.5 ± 4.9 cm; 25.2 ± 6.2 vs. 22.7 ± 5.0 cm). However, middle-aged adults showed longer ground contact times (on average 36%), lower vertical ground reaction forces (36%) and hence lower average mechanical power (from lowest to highest box height: 2266 ± 563 vs. 1498 ± 545 W; 3563 ± 774 vs. 2222 ± 320 W; 4360 ± 658 vs. 2475 ± 528 W; 5008 ± 919 vs. 3034 ± 435 W) independent of box height. Further, leg stiffness was lower (48%) in middle-aged compared to younger adults for all jumping conditions and we found significant correlations between average mechanical power and leg stiffness (0.70 ≤ r ≤ 0.83; p < 0.01). Thus, while jumping performance appears to be unaffected when leg extensor muscle strength and tendon stiffness are maintained, the reduced muscular power output during lower limb multi-joint tasks seen with aging may be due to age-related changes in motor task execution strategy rather than due to muscle weakness.

Muscle-Bone Interactions in Pediatric Bone Diseases

PURPOSE

Here, we review the skeletal effects of pediatric muscle disorders as well as muscle impairment in pediatric bone disorders.

RECENT FINDINGS

When starting in utero, muscle disorders can lead to congenital multiple contractures. Pediatric-onset muscle weakness such as cerebral palsy, Duchenne muscular dystrophy, spinal muscular atrophy, or spina bifida typically are associated with small diameter of long-bone shafts, low density of metaphyseal bone, and increased fracture incidence in the lower extremities, in particular, the distal femur. Primary bone diseases can affect muscles through generic mechanisms, such as decreased physical activity or in disease-specific ways. For example, the collagen defect underlying the bone fragility of osteogenesis imperfecta may also affect muscle force generation or transmission. Transforming growth factor beta released from bone in Camurati Engelman disease may decrease muscle function.

FUTURE DIRECTIONS

Considering muscle-bone interactions does not only contribute to the understanding of musculoskeletal disorders but also can identify new targets for therapeutic interventions.

Improved single muscle fiber quality in the oldest-old

We examined single muscle fiber contractile function of the oldest-old (3F/2M, 89 ± 1 yr old) enrolled in The Health, Aging, and Body Composition Study (The Health ABC Study). Vastus lateralis muscle biopsies were obtained and single muscle fiber function was determined (n = 105) prior to myosin heavy chain (MHC) isoform identification with sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Cross-sectional area of MHC I muscle fibers (5,576 ± 333 μm²; n = 58) was 21% larger (P < 0.05) than MHC IIa fibers (4,518 ± 386 μm²; n = 47). Normalized power (an indicator of muscle fiber quality incorporating size, strength, and speed) of MHC I and IIa muscle fibers was 2.3 ± 0.1 and 17.4 ± 0.8 W/l, respectively. Compared with previous research from our lab using identical procedures, MHC I normalized power was 28% higher than healthy 20 yr olds and similar to younger octogenarians (∼80 yr old). Normalized power of MHC IIa fibers was 63% greater than 20 yr olds and 39% greater than younger octogenarians. These comparative data suggest that power output per unit size (i.e., muscle quality) of remaining muscle fibers improves with age, a phenomenon more pronounced in MHC IIa fibers. Age-related single muscle fiber quality improvements may be a compensatory mechanism to help offset decrements in whole muscle function.

Age-dependent Muscle Adaptation after Chronic Stretch-shortening Contractions in Rats

Age-related differences in contraction-induced adaptation have been well characterized especially for young and old rodent models but much less so at intermediate ages. Therefore, additional research is warranted to determine to what extent alterations in adaptation are due to maturation versus aging per se. The purpose of our study was to evaluate muscles of Fisher 344XBrown Norway rats of various ages following one month of exposure to stretch-shortening contractions (SSCs). With exposure, muscles mass increased by ~10% for 27 and 30 month old rats vs. ~20% for 3 and 6 month old rats (P < 0.05). For 3 month old rats, maximum isometric force and dynamic peak force increased by 22 ± 8% and 27 ± 10%, respectively (P < 0.05). For 6 month old rats, these forces were unaltered by exposure and positive work capacity diminished by 27 ± 2% (P = 0.006). By 30 months of age, age-related deficits in maximum isometric force, peak force, negative work, and positive work were apparent and SSC exposure was ineffective at counteracting such deficits. Recovery from fatigue was also tested and exposure-induced improvements in fatigue recovery were indicated for 6 month old rats and to a lesser extent for 3 month old rats whereas no such effect was observed for older rats. Alterations in fatigue recovery were accompanied by evidence of substantial type IIb to IIx fiber type shifting. These results highlight the exceptional adaptive capacity for strength at a young age, the inclination for adaptation in fatigue recovery at early adulthood, and diminished adaptation for muscle performance in general beginning at late adulthood. Such findings motivate careful investigation to determine appropriate SSC exposures at all stages of life.

The impact of obesity on skeletal muscle strength and structure through adolescence to old age

Obesity is associated with functional limitations in muscle performance and increased likelihood of developing a functional disability such as mobility, strength, postural and dynamic balance limitations. The consensus is that obese individuals, regardless of age, have a greater absolute maximum muscle strength compared to non-obese persons, suggesting that increased adiposity acts as a chronic overload stimulus on the antigravity muscles (e.g., quadriceps and calf), thus increasing muscle size and strength. However, when maximum muscular strength is normalised to body mass, obese individuals appear weaker. This relative weakness may be caused by reduced mobility, neural adaptations and changes in muscle morphology. Discrepancies in the literature remain for maximal strength normalised to muscle mass (muscle quality) and can potentially be explained through accounting for the measurement protocol contributing to muscle strength capacity that need to be explored in more depth such as antagonist muscle co-activation, muscle architecture, a criterion valid measurement of muscle size and an accurate measurement of physical activity levels. Current evidence demonstrating the effect of obesity on muscle quality is limited. These factors not being recorded in some of the existing literature suggest a potential underestimation of muscle force either in terms of absolute force production or relative to muscle mass; thus the true effect of obesity upon skeletal muscle size, structure and function, including any interactions with ageing effects, remains to be elucidated.

NMR based biomarkers to study age-related changes in the human quadriceps

Age-related sarcopenia is a major health issue. To improve elderly person quality of life, it is important to characterize age-associated structural changes within the skeletal muscle. NMR imaging offers quantitative tools to monitor these changes. We scanned 93 subjects: 33 young adults aged between 19 and 27 years old and 60 older adults between 69 and 80 years old. Their physical activity was assessed using a tri-axial accelerometer and they were classified either as active or sedentary. A standard multi-slice multi-echo (MSME) sequence was run and water T2 maps were extracted using a tri-exponential fit. Fat fraction was quantified using three-point Dixon technique. Each quadriceps muscle was characterized by: water T2 mean value, water T2 heterogeneity and the mean fat fraction. Statistical analysis (ANOVA) showed that water T2 mean values and its heterogeneity indices as well as fat fraction were significantly higher in the elderly group (p<0.05). Only fat fraction was significantly lower in the active group compared to the sedentary one (p<0.05). Linear regression confirmed the significant impact of age on these NMR parameters whereas physical activity impact was not systematic. NMR imaging provided a comprehensive assessment of the aging process impact on skeletal muscle composition. Water T2 increase might be related to changes in fiber typology while increased T2 heterogeneities might correlate with some degree of tissue disorganization, like the development of interstitial fibrosis. Fat fraction and water T2 heterogeneity increase was partly slowed down by physical activity. These changes were not gender dependent.

FAST CP: protocol of a randomised controlled trial of the efficacy of a 12-week combined Functional Anaerobic and Strength Training programme on muscle properties and mechanical gait deficiencies in adolescents and young adults with spastic-type cerebral palsy

INTRODUCTION

Individuals with cerebral palsy (CP) have muscles that are smaller, weaker and more resistant to stretch compared to typically developing people. Progressive resistance training leads to increases in muscle size and strength. In CP, the benefits of resistance training alone may not transfer to improve other activities such as walking; however, the transfer of strength improvements to improved mobility may be enhanced by performing training that involves specific functional tasks or motor skills. This study aims to determine the efficacy of combined functional anaerobic and strength training in (1) influencing muscle strength, structure and function and (2) to determine if any changes in muscle strength and structure following training impact on walking ability and gross motor functional capacity and performance in the short (following 3 months of training) and medium terms (a further 3 months post-training).

METHODS AND ANALYSIS

40 adolescents and young adults with CP will be recruited to undertake a 12-week training programme. The training programme will consist of 3 × 75 min sessions per week, made up of 5 lower limb resistance exercises and 2-3 functional anaerobic exercises per session. The calf muscles will be specifically targeted, as they are the most commonly impacted muscles in CP and are a key muscle group involved in walking. If, as we believe, muscle properties change following combined strength and functional training, there may be long-term benefits of this type of training in slowing the deterioration of muscle function in people with spastic-type CP.

ETHICS AND DISSEMINATION

Ethical approval has been obtained from the ethics committees at The University of Queensland (2014000066) and Children's Health Queensland (HREC/15/QRCH/30). The findings will be disseminated by publications in peer-reviewed journals, conferences and local research organisations' media.

TRIAL REGISTRATION NUMBER

Australian and New Zealand Clinical Trials Registry (ACTRN12614001217695).

C57BL/6 life span study: age-related declines in muscle power production and contractile velocity

Quantification of key outcome measures in animal models of aging is an important step preceding intervention testing. One such measurement, skeletal muscle power generation (force * velocity), is critical for dynamic movement. Prior research focused on maximum power (P max), which occurs around 30-40 % of maximum load. However, movement occurs over the entire load range. Thus, the primary purpose of this study was to determine the effect of age on power generation during concentric contractions in the extensor digitorum longus (EDL) and soleus muscles over the load range from 10 to 90 % of peak isometric tetanic force (P 0). Adult, old, and elderly male C57BL/6 mice were examined for contractile function (6-7 months old, 100 % survival; ~24 months, 75 %; and ~28 months, <50 %, respectively). Mice at other ages (5-32 months) were also tested for regression modeling. We hypothesized and found that power decreased with age not only at P max but also over the load range. Importantly, we found greater age-associated deficits in both power and velocity when the muscles were contracting concentrically against heavy loads (>50 % P 0). The shape of the force-velocity curve also changed with age (a/P 0 increased). In addition, there were prolonged contraction times to maximum force and shifts in the distribution of the myosin light and heavy chain isoforms in the EDL. The results demonstrate that age-associated difficulty in movement during challenging tasks is likely due, in addition to overall reduced force output, to an accelerated deterioration of power production and contractile velocity under heavily loaded conditions.

Community-dwelling female fallers have lower muscle density in their lower legs than non-fallers: evidence from the Saskatoon Canadian Multicentre Osteoporosis Study (CaMos) cohort

OBJECTIVES

Our objectives were to determine whether peripheral quantitative computed tomography (pQCT)-derived lower leg muscle density and area, and basic functional mobility differ between community-dwelling older women who do and do not report recent falls.

DESIGN

Matched case-control comparison.

SETTING

Academic biomedical imaging laboratory.

PARTICIPANTS

147 Women, 60 years or older (mean age 74.3 y, SD 7.7) recruited from a longitudinal, population-based cohort representing community-dwelling residents in the area of Saskatoon, Canada.

MEASUREMENTS

A cross-sectional pQCT scan of the non-dominant lower leg was acquired to determine muscle density and area. Basic functional mobility (Timed Up and Go Test [TUG]) and SF36 health status were also measured. Fallers (one or more falls) and non-fallers (no falls) were grouped according to a 12-month retrospective survey and matched on measured covariates.

RESULTS

The muscle density of fallers (n = 35) was a median of 2.1 mg/cm3 lower (P = 0.019, 95% C.I. -3.9 to -0.1) than non-fallers (n = 78) after matching and adjusting for age, body mass index, and SF36 general health scores. Muscle area and TUG did not differ between fallers and non-fallers.

CONCLUSIONS

Muscle density may serve as a physiological marker in the assessment of lower leg muscular health and fall risk in community-dwelling elderly women. These results are limited to our study population who were mostly Caucasian. Prospective studies are required for verification.

Combined effects of body composition and ageing on joint torque, muscle activation and co-contraction in sedentary women

This study aimed to establish the interplay between body mass, adiposity, ageing and determinants of skeletal muscle strength. One hundred and two untrained healthy women categorised by age into young (Y) (mean ± SD, 26.7 ± 9.4 years) vs. old (O) (65.1 ± 7.2 years) were assessed for body fat, lean mass, plantar flexion and dorsiflexion maximum voluntary isometric contraction (MVC) torque, muscle activation capacity and antagonist muscle co-contraction. MVC torque normalised to body mass in the obese group was 35 and 29 % lower (p < 0.05) in Y and 34 and 31 % lower (p < 0.05) in O, compared with underweight and normal weight individuals, respectively. Y with ≥40 % body fat had significantly lower activation than Y with <40 % body fat (88.3 vs. 94.4 %, p < 0.05), but O did not exhibit this effect. Co-contraction was affected by ageing (16.1 % in O vs. 13.8 % in Y, p < 0.05) but not body composition. There were significant associations between markers of body composition, age, strength and activation capacity, with the strongest correlation between muscle strength and total body mass (r (2) = 0.508 in Y, p < 0.001, vs. r (2) = 0.204 in O, p < 0.01). Furthermore, the age-related loss in plantar flexion (PF) MVC torque was exacerbated in obese compared to underweight, normal weight and overweight individuals (-0.96 vs. -0.54, -0.57 and -0.57 % per year, p < 0.05). The negative impact of adiposity on muscle performance is associated with not only muscular but also neural factors. Overall, the effects of ageing and obesity on this system are somewhat cumulative.

Peripheral nerve function and lower extremity muscle power in older men

OBJECTIVE

To assess whether sensorimotor peripheral nerve function is associated with muscle power in community-dwelling older men.

DESIGN

Longitudinal cohort study with 2.3±0.3 years of follow-up.

SETTING

One clinical site.

PARTICIPANTS

Participants (n=372; mean age ± SD, 77.2±5.1y; 99.5% white; body mass index, 27.9±3.7kg/m(2); power, 1.88±0.6W/kg) at 1 site of the Osteoporotic Fractures in Men Study (N=5994).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

A nerve function ancillary study was performed 4.6±0.4 years after baseline. Muscle power was measured using a power rig. Peroneal motor nerve conduction amplitude, distal motor latency, and mean f-wave latency were measured. Sensory nerve function was assessed using 10-g and 1.4-g monofilaments and sural sensory nerve conduction amplitude and distal latency. Peripheral neuropathy symptoms at the leg and feet were assessed by self-report.

RESULTS

After adjustments for age, height, and total body lean and fat mass, 1 SD lower motor (β=-.07, P<.05) and sensory amplitude (β=-.09, P<.05) and 1.4-g (β=-.11, P<.05) and 10-g monofilament insensitivity (β=-.17, P<.05) were associated with lower muscle power/kg. Compared with the effect of age on muscle power (β per year, -.05; P<.001), this was equivalent to aging 1.4 years for motor amplitude, 1.8 years for sensory amplitude, 2.2 years for 1.4-g monofilament detection, and 3.4 years for 10-g detection. Baseline 1.4-g monofilament detection predicted a greater decline in muscle power/kg. Short-term change in nerve function was not associated with concurrent short-term change in muscle power/kg.

CONCLUSIONS

Worse sensory and motor nerve function were associated with lower muscle power/kg and are likely important for impaired muscle function in older men. Monofilament sensitivity was associated with a greater decline in muscle power/kg, and screening may identify an early risk for muscle function decline in late life, which has implications for disability.

The effect of knee joint angle on plantar flexor power in young and old men

Human adult aging is associated with a loss of strength, contractile velocity and hence, power. The principal plantar flexors, consisting of the bi-articular gastrocnemeii and the mono-articular soleus, appear to be affected differently by the aging process. However, the age-related effect of knee joint angle on the torque-angular velocity relationship and power production of this functionally important muscle group is unknown. The purpose was to determine whether flexing the knee, thereby reducing the gastrocnemius contribution to plantar flexion, would exacerbate the age-related decrements in plantar flexion power, or shift the torque-angular velocity relationship differently in older compared with young men. Neuromuscular properties were recorded from 10 young (~25 y) and 10 old (~78 y) men with the knee extended (170°) and flexed (90°), in a randomized order. Participants performed maximal voluntary isometric contractions (MVCs), followed by maximal velocity-dependent shortening contractions at pre-set loads, ranging from 15 to 75% MVC. The young men were ~20-25% stronger, ~12% faster and ~30% more powerful than the old for both knee angles (P<0.05). In both age groups, isometric MVC torque was ~17% greater in the extended than flexed knee position, with no differences in voluntary activation (>95%). The young men produced 7-12% faster angular velocities in the extended knee position for loads ≤30% MVC, but no differences at higher loads; whereas there were no detectable differences in angular velocity between knee positions in the old across all relative loads. For both knee angles, young men produced peak power at 43.3±9.0% MVC, whereas the old men produced peak power at 54.8±7.9% MVC. These data indicate that the young, who have faster contracting muscles compared with the old, can rely more on velocity than torque for generating maximal power.

Plantar flexor moment arm and muscle volume predict torque-generating capacity in young men

Muscle volume is known to correlate with maximal joint torque in humans, but the role of muscle moment arm in determining maximal torque is less clear. Moderate correlations have been reported between maximal isometric knee extensor torque and knee extensor moment arm, but no such observations have been made for the ankle joint. It has been suggested that smaller muscle moment arms may enhance force generation at high rates of joint rotation, but this has not yet been observed for ankle muscles in vivo. The purpose of the present study was to correlate plantar flexor moment arm and plantar flexor muscle volume with maximal plantar flexor torque measured at different rates of plantar flexion. Magnetic resonance imaging was used to quantify the plantar flexor moment arm and muscle volume of the posterior compartment in 20 healthy young men. Maximal plantar flexor torque was measured isometrically and at three plantar flexion speeds using an isokinetic dynamometer. Plantar flexor torque was significantly correlated with muscle volume (0.222 < R(2) < 0.322) and with muscle moment arm at each speed (0.323 < R(2) < 0.494). While muscle volume was strongly correlated with body mass and stature, moment arm was not. The slope of the torque-moment arm regression line decreased as the rate of joint rotation increased, indicating that subjects with small moment arms experienced smaller reductions in torque at high speeds. The findings of this study suggest that plantar flexor moment arm is a determinant of joint strength that is at least as important as muscle size.

Human neuromuscular structure and function in old age: A brief review

Natural adult aging is associated with many functional impairments of the human neuromuscular system. One of the more observable alterations is the loss of contractile muscle mass, termed sarcopenia. The loss of muscle mass occurs primarily due to a progressive loss of viable motor units, and accompanying atrophy of remaining muscle fibers. Not only does the loss of muscle mass contribute to impaired function in old age, but alterations in fiber type and myosin heavy chain isoform expression also contribute to weaker, slower, and less powerful contracting muscles. This review will focus on motor unit loss associated with natural adult aging, age-related fatigability, and the age-related differences in strength across contractile muscle actions.

Muscle Quality in Older Adults

The population of older adults in the United States is steadily growing and identifying factors that contribute to healthy aging is a public health priority. Changes in body composition are a hallmark of the aging process and have been implicated in the loss of physical function among older adults. In particular, age-related declines in muscle strength and power occur at a faster rate than the loss of muscle mass (sarcopenia), and this suggests a decrease in muscle quality of older adults. Muscle quality has traditionally been defined as muscle function (strength or power) per unit of muscle size (mass or cross-sectional area) and a growing body of literature suggests that lower body muscle quality may be critical for maintaining functional independence with age. However, the literature regarding the definition of muscle quality and its relationship with health outcomes in older adults has not been adequately reviewed. Thus, the aim of this report is to highlight the contemporary literature regarding age-related changes in muscle quality and its relationship with health outcomes in community-dwelling older adults.

Dual-joint modeling for estimation of total knee replacement contact forces during locomotion

Model-based estimation of in vivo contact forces arising between components of a total knee replacement is challenging because such forces depend upon accurate modeling of muscles, tendons, ligaments, contact, and multibody dynamics. Here we describe an approach to solving this problem with results that are tested by comparison to knee loads measured in vivo for a single subject and made available through the Grand Challenge Competition to Predict in vivo Tibiofemoral Loads. The approach makes use of a "dual-joint" paradigm in which the knee joint is alternately represented by (1) a ball-joint knee for inverse dynamic computation of required muscle controls and (2) a 12 degree-of-freedom (DOF) knee with elastic foundation contact at the tibiofemoral and patellofemoral articulations for forward dynamic integration. Measured external forces and kinematics were applied as a feedback controller and static optimization attempted to track measured knee flexion angles and electromyographic (EMG) activity. The resulting simulations showed excellent tracking of knee flexion (average RMS error of 2.53 deg) and EMG (muscle activations within ±10% envelopes of normalized measured EMG signals). Simulated tibiofemoral contact forces agreed qualitatively with measured contact forces, but their RMS errors were approximately 25% of the peak measured values. These results demonstrate the potential of a dual-joint modeling approach to predict joint contact forces from kinesiological data measured in the motion laboratory. It is anticipated that errors in the estimation of contact force will be reduced as more accurate subject-specific models of muscles and other soft tissues are developed.

Neuromechanical properties of the triceps surae in young and older adults

The aim of this study was to compare voluntary and involuntary force generating capacity of the triceps surae muscles in healthy young and older adult participants during isometric and isokinetic contractions. Ultrasound was used to measure medial gastrocnemius (MG) fascicle length during maximal voluntary isometric contractions and supra-maximal isometric twitch contractions at five ankle angles throughout the available range of motion, as well as isokinetic concentric and eccentric contractions at four ankle velocities. Maximum voluntary activation of the plantar flexors was assessed using the twitch interpolation technique. Peak plantar flexor torque was significantly lower in older adults compared to young participants by 42%, 28% and 43% during maximal voluntary isometric contractions, supra-maximal isometric twitch and concentric contractions respectively. No age-related differences in eccentric torque production were detected. When age-related differences in triceps surae muscle volume determined from MRI were taken into account, the age-related peak plantar flexor torque deficits for maximum voluntary isometric, supra-maximal twitch, and concentric contractions were 24%, 19% and 24% respectively. These age-related differences in torque were not explained by torque-length-velocity behaviour of the MG muscle fascicles, passive plantar flexor torque-angle properties, decreased neural drive of the plantar flexor muscles or antagonistic co-activation of the tibialis anterior muscle. The residual deficit in isometric and concentric plantar flexor torques in healthy older adults may involve reduced muscle quality. A significant reduction in supra-maximal twitch torque at longer MG fascicle lengths as well as a lower MG fascicle velocity during eccentric contractions in older adults was detected, which could possibly be a function of the reported increased Achilles tendon compliance in older adults.

Neuromuscular determinants of maximum walking speed in well-functioning older adults

Maximum walking speed may offer an advantage over usual walking speed for clinical assessment of age-related declines in mobility function that are due to neuromuscular impairment. The objective of this study was to determine the extent to which maximum walking speed is affected by neuromuscular function of the lower extremities in older adults. We recruited two groups of healthy, well functioning older adults who differed primarily on maximum walking speed. We hypothesized that individuals with slower maximum walking speed would exhibit reduced lower extremity muscle size and impaired plantarflexion force production and neuromuscular activation during a rapid contraction of the triceps surae muscle group (soleus (SO) and gastrocnemius (MG)). All participants were required to have usual 10-meter walking speed of >1.0m/s. If the difference between usual and maximum 10m walking speed was <0.6m/s, the individual was assigned to the "Slower" group (n=8). If the difference between usual and maximum 10-meter walking speed was >0.6m/s, the individual was assigned to the "Faster" group (n=12). Peak rate of force development (RFD) and rate of neuromuscular activation (rate of EMG rise) of the triceps surae muscle group were assessed during a rapid plantarflexion movement. Muscle cross sectional area of the right triceps surae, quadriceps and hamstrings muscle groups was determined by magnetic resonance imaging. Across participants, the difference between usual and maximal walking speed was predominantly dictated by maximum walking speed (r=.85). We therefore report maximum walking speed (1.76 and 2.17m/s in Slower and Faster, p<.001) rather than the difference between usual and maximal. Plantarflexion RFD was 38% lower (p=.002) in Slower compared to Faster. MG rate of EMG rise was 34% lower (p=.01) in Slower than Faster, but SO rate of EMG rise did not differ between groups (p=.73). Contrary to our hypothesis, muscle CSA was not lower in Slower than Faster for the muscle groups tested, which included triceps surae (p=.44), quadriceps (p=.76) and hamstrings (p=.98). MG rate of EMG rise was positively associated with RFD and maximum 10m walking speed, but not the usual 10m walking speed. These findings support the conclusion that maximum walking speed is limited by impaired neuromuscular force and activation of the triceps surae muscle group. Future research should further evaluate the utility of maximum walking speed for use in clinical assessment to detect and monitor age-related functional decline.

A qualitative review of balance and strength performance in healthy older adults: impact for testing and training

A continuously greying society is confronted with specific age-related health problems (e.g., increased fall incidence/injury rate) that threaten both the quality of life of fall-prone individuals as well as the long-term sustainability of the public health care system due to high treatment costs of fall-related injuries (e.g., femoral neck fracture). Thus, intense research efforts are needed from interdisciplinary fields (e.g., geriatrics, neurology, and exercise science) to (a) elucidate neuromuscular fall-risk factors, (b) develop and apply adequate fall-risk assessment tools that can be administered in clinical practice, and (c) develop and design effective intervention programs that have the potential to counteract a large number of fall-risk factors by ultimately reducing the number of falls in the healthy elderly. This paper makes an effort to present the above-raised research topics in order to provide clinicians, therapists, and practitioners with the current state-of-the-art information.

How to assess functional status: a new muscle quality index

Aging is associated with decreases in muscle mass, muscle strength and muscle power, with muscle strength declining at a higher rate than muscle mass, but at a lower rate than muscle power. This progressive mismatch suggests a deterioration of muscle "quality" that may lead to functional incapacities. Although it may be difficult to synthesize the concept of muscle quality, the aim of the present paper was to propose a clinical definition of muscle quality in regard to the functional status. Accordingly, the muscle strength or muscle power per unit of muscle mass ratios appear to be clinically relevant markers of muscle quality. Several mechanisms susceptible to influence these ratios have been described, among which age, gender, sex hormones, obesity, physical activity and fibrosis. Various methods to assess muscle quality in both the clinical and research fields have also been listed, with a particular interest for the tests used to measure muscle power. Finally, we proposed a clinical screening tool to detect individuals at risk of functional incapacities. Briefly, the muscle quality score is based on handgrip strength assessment by hand dynamometer, muscle mass measurement by bioelectrical analysis, and leg muscle power estimation using a chair stand test.

Skeletal muscle properties in rheumatoid arthritis patients

PURPOSE

Disability in patients with rheumatoid arthritis (RA) is a multifactorial process involving various unaccounted factors. Loss of lean body mass plays an important role in impaired physical function, and exercise studies in RA have shown promising results in restoring muscle mass, strength, and function. However, no comprehensive assessment of the muscle characteristics has been undertaken to determine whether qualitative changes in muscle also contribute to RA disability. This study explores the physiological muscle properties of a community-based population with stable RA.

METHODS

Vastus lateralis (VL) force and physiological cross-sectional area (PCSA), voluntary muscle activation capacity, and contractile properties were assessed in 23 patients with stable RA (age = 60 ± 2 yr (mean ± SEM); 16 women) and age- and sex-matched healthy controls (age = 60 ± 3 yr). Measurements with EMG were obtained during maximal isometric knee extension contractions, with resting and superimposed electrical stimulations. Concentric knee extension contractions were also assessed. Pennation angle and VL volume were measured with ultrasound to determine fiber fascicle length and PCSA. Muscle-specific force was calculated (VL force/VL PCSA). Body composition using dual-energy x-ray absorptiometry and objective physical function were also measured.

RESULTS

The patients displayed typical features of RA with reduced physical function (P = 0.001-0.09), a trend toward lower appendicular lean mass (P = 0.09) and increased total body fat (P < 0.05) relative to controls. However, there were no differences in specific force, contractile properties, voluntary activation capacity, and contraction velocity (P = 0.41-0.99). VL PCSA was reduced (P < 0.05) with minor architectural changes in patients with RA.

CONCLUSIONS

Physiological properties of muscle that determine specific force are not compromised in patients with stable RA despite deficits in physical function.

Contractile and non-contractile tissue volume and distribution in ankle muscles of young and older adults

Magnetic resonance imaging (MRI) enables accurate in vivo quantification of human muscle volumes, which can be used to estimate subject-specific muscle force capabilities. An important consideration is the amount of contractile and non-contractile tissue in the muscle compartment, which will influence force capability. We quantified age-related differences in the proportion and distribution of contractile and non-contractile tissue in the dorsiflexor and plantar flexor (soleus, and medial and lateral heads of gastrocnemius) muscles, and examined how well these volumes can be estimated from single MRI cross-sections. Axial MRIs of the left leg for 12 young (mean age 27 years) and 12 older (72 years) healthy, active adults were used to compute muscle volumes. Contractile tissue distribution along the leg was characterized by mathematical functions to allow volume prediction from single-slice cross-sectional area (CSA) measurements. Compared to young, older adults had less contractile volume and a greater proportion of non-contractile tissue. In both age groups the proportion of non-contractile tissue increased distally, with the smallest proportion near the maximum compartment CSA. A single CSA measurement predicted contractile volume with 8-11% error, with older adults in the higher end of this range. Using multiple slices improved volume estimates by roughly 50%, with average errors of about 3-4%. These results demonstrate significant age-related differences in non-contractile tissue for the dorsi- and plantar-flexor muscles. Although estimates of contractile volume can be obtained from single CSA measurements, multiple slices are needed for increased accuracy due to inter-individual variations in muscle volume and composition.

Power loss is greater in old men than young men during fast plantar flexion contractions

It is unclear during human aging whether healthy older adults (>70 yr old) experience greater, lesser, or the same fatigability compared with younger adults. The reported disparate findings may be related to the task-dependent nature of fatigue and the limited number of studies exploring nonisometric contractile function and aging. The purpose here was to determine the effects of fast shortening contractions on the fatigability of the triceps surae in 10 young (~24 yr old) and 10 old (~78 yr old) men using isometric and dynamic measures. Participants performed 50 maximal velocity-dependent plantar flexions at a constant load of 20% maximal voluntary isometric contraction (MVC). Isometric twitch properties and MVCs were tested at baseline and during and following the fatigue task. Voluntary activation was similar between the old and young (~98%) and was unaltered with fatigue. The old had 26% lower (P < 0.01) isometric MVC torque and 18% slower (P < 0.01) maximal shortening velocity than the young. Hence, peak power was 38% lower in the old (P < 0.01). At task termination, MVC torque was maintained in the old (P = 0.15) but decreased by 21% in the young (P < 0.01). Twitch half-relaxation time was lengthened in the old at task termination by 26% (P < 0.01) but unchanged in the young (P = 0.10). Peak power was reduced by 24% and 17% at task termination in the old and young, respectively (P < 0.01). Despite a better maintenance in isometric MVC torque production, the weaker and slower contracting triceps surae of the old was more fatigable than the young during fast dynamic efforts with an unconstrained velocity.

Voluntary activation failure contributes more to plantar flexor weakness than antagonist coactivation and muscle atrophy in chronic stroke survivors

The contributions of nervous system muscle activation and muscle atrophy to poststroke weakness have not been evaluated together in the same subject. Maximal voluntary contraction (MVC) torque, voluntary activation (twitch interpolation), and electromyographic (EMG) amplitude were determined bilaterally in the plantar flexors of seven chronic stroke survivors (40-63 yr, 24-51 mo poststroke). Volumes of the plantar flexor muscles were determined bilaterally with magnetic resonance imaging (MRI). The mean (±SD) contralesional (paretic) MVC torque was less than one-half of the ipsilesional leg: 56.7 ± 57.4 vs. 147 ± 35.7 Nm (P = 0.006). Contralesional voluntary activation was only 48 ± 36.9%, but was near complete in the ipsilesional leg, 97 ± 1.9% (P = 0.01). The contralesional MVC EMG amplitude (normalized to the maximum M-wave peak-to-peak amplitude) of the gastrocnemii and soleus were 36.0 ± 28.5 and 36.0 ± 31.0% of the ipsilesional leg. Tibialis anterior (TA) EMG coactivation was not different between the contralesional (23.2 ± 24.0% of TA MVC EMG) and ipsilesional side (12.3 ± 5.7%) (P = 0.24). However, TA EMG coactivation was excessive (71%) in one subject and accounted for ~8% of her weakness based on the estimated antagonist torque. Relative (%ipsilesional leg) plantar flexor and gastrocnemii volumes were 88 ± 6% (P = 0.004) and 76 ± 15% (P = 0.01), respectively. Interlimb volume differences of the soleus, deep plantar flexors, and peronei were not significant. Preferred walking speed (0.83 ± 0.33 m/s) was related to the contralesional MVC torque (r(2) = 0.57, P = 0.05, N = 7), but the two subjects with the greatest weakness walked faster than three others. Our findings suggest that plantar flexor weakness in mobile chronic stroke survivors reflects mostly voluntary activation failure, with smaller contributions from antagonist activity and atrophy.

Effect of exercise intervention on thigh muscle volume and anatomical cross-sectional areas--quantitative assessment using MRI

The objective of this study was to evaluate the location-specific magnitudes of an exercise intervention on thigh muscle volume and anatomical cross-sectional area, using MRI. Forty one untrained women participated in strength, endurance, or autogenic training for 12 weeks. Axial MR images of the thigh were acquired before and after the intervention, using a T1-weighted turbo-spin-echo sequence (10 mm sections, 0.78 mm in-plane resolution). The extensor, flexor, adductor, and sartorius muscles were segmented between the femoral neck and the rectus femoris tendon. Muscle volumes were determined, and anatomical cross-sectional areas were derived from 3D reconstructions at 10% (proximal-to-distal) intervals. With strength training, the volume of the extensors (+3.1%), flexors (+3.5%), and adductors (+3.9%) increased significantly (P < 0.05) between baseline and follow-up, and with endurance training, the volume of the extensor (+3.7%) and sartorius (+5.1%) increased significantly (P < 0.05). No relevant or statistically significant change was observed with autogenic training. The greatest standardized response means were observed for the anatomical cross-sectional area in the proximal aspect (10-30%) of the thigh and generally exceeded those for muscle volumes. The study shows that MRI can be used to monitor location-specific effects of exercise intervention on muscle cross-sectional areas, with the proximal aspect of the thigh muscles being most responsive.

Aging and the force-velocity relationship of muscles

Aging in humans is associated with a loss in neuromuscular function and performance. This is related, in part, to the reduction in muscular strength and power caused by a loss of skeletal muscle mass (sarcopenia) and changes in muscle architecture. Due to these changes, the force-velocity (f-v) relationship of human muscles alters with age. This change has functional implications such as slower walking speeds. Different methods to reverse these changes have been investigated, including traditional resistance training, power training and eccentric (or eccentrically-biased) resistance training. This review will summarise the changes of the f-v relationship with age, the functional implications of these changes and the various methods to reverse or at least partly ameliorate these changes.

Triceps surae contractile properties and firing rates in the soleus of young and old men

Mean maximal motor unit firing rates (MUFRs) of the human soleus are lower (5-20 Hz) than other limb muscles (20-50 Hz) during brief sustained contractions. With healthy adult aging, maximal MUFRs are 20-40% lower and twitch contractile speed of lower limb muscles are 10-40% slower compared with young adults. However, it is unknown whether the inherently low maximal MUFRs for the soleus are further reduced with aging in association with age-related slowing in contractile properties. The purpose of the present study was to compare the changes in triceps surae contractile properties and MUFRs of the soleus throughout a variety of contraction intensities in six old ( approximately 75 yr old) and six young ( approximately 24 yr old) men. Neuromuscular measures were collected from the soleus and triceps surae during repeated sessions (2-6 sessions). Populations of single MUFR trains were recorded from the soleus with tungsten microelectrodes during separate sustained 6- to 10-s isometric contractions of varying intensities [25%, 50%, 75%, and 100% maximal voluntary isometric contraction (MVC)]. The old men had weaker triceps surae strength (MVC; 35% lower) and slower contractile properties (contraction duration; 20% longer) than the young men. However, there was no difference in average MUFRs of the soleus at 75% and 100% MVC ( approximately 14.5 Hz and approximately 16.5 Hz, respectively). At 25% and 50% MVC, average rates were 10% and 20% lower in the old men compared with young, respectively. Despite a significant slowing in triceps surae contraction duration, there was no age-related change in MUFRs recorded at high contractile intensities in the soleus. Thus the relationship between the whole muscle contractile properties and MUFRs found in other muscle groups may not exist between the triceps surae and soleus and may be muscle dependent.

Interaction between muscle temperature and contraction velocity affects mechanical efficiency during moderate-intensity cycling exercise in young and older women

The effect of elevated muscle temperature on mechanical efficiency was investigated during exercise at different pedal frequencies in young and older women. Eight young (24 +/- 3 yr) and eight older (70 +/- 4 yr) women performed 6-min periods of cycling at 75% ventilatory threshold at pedal frequencies of 45, 60, 75, and 90 rpm under control and passively elevated local muscle temperature conditions. Mechanical efficiency was calculated from the ratio of energy turnover (pulmonary O(2) uptake) and mechanical power output. Overall, elevating muscle temperature increased (P < 0.05) mechanical efficiency in young (32.0 +/- 3.1 to 34.0 +/- 5.5%) and decreased (P < 0.05) efficiency in older women (30.2 +/- 5.6 to 27.9 +/- 4.1%). The different effect of elevated muscle temperature in young and older women reflects a shift in the efficiency-velocity relationship of skeletal muscle. These effects may be due to differences in recruitment patterns, as well as sarcopenic and fiber-type changes with age.

Potential role of optimal velocity as a qualitative factor of physical functional performance in women aged 72 to 96 years

OBJECTIVE

To assess the relationship of maximal leg power and its corresponding determinants (eg, optimal velocity and optimal torque) measured during maximal voluntary knee extension to physical functional performance of older women.

DESIGN

Descriptive.

SETTING

Community retirement homes.

PARTICIPANTS

Women (N=39) aged 72 to 96 years.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Volunteers performed in sitting position maximal knee extensions on an Ergopower dynamometer to calculate maximal leg power, optimal velocity, and optimal torque. Three standardized tests were also performed to evaluate physical performance: walking speed over 6m, time taken to rise 5 times from a chair, and time to climb 6 stairs.

RESULTS

On multiple regression analysis, leg power (mean, 1.37+/-0.80 W/kg) significantly correlated with physical performance as measured by 6-m walking speed (mean, .85+/-.40 m/s), chair-stand time (mean, 16.3+/-7.7s), and stair-climb time (mean, 7+/-4s), describing 16% to 33% of the variance. Optimal velocity (mean, 1.79+/-1.20 rad/s) also significantly correlated with 6-m walking speed, chair-stand time, and stair-climb time, describing 46% to 89% of the variance. Optimal torque (50.8+/-16.9 Nm) did not correlate with physical performance.

CONCLUSIONS

Maximal power and moreover optimal velocity were thus found to be determinants of physical performance, both appearing as significant mobility factors in older adults. This may provide more focus on velocity-oriented training as a means of improving functional status.