Age differences in knee extension power, contractile velocity, and fatigability

Knee muscle strength and steadiness for individuals with anterior cruciate ligament reconstruction and knee osteoarthritis

BACKGROUND

Strength and neuromuscular decrements following knee musculoskeletal injury may accelerate knee osteoarthritis development. This study assessed isometric knee extensor and flexor strength and steadiness between individuals with knee injury, i.e., ligament reconstruction, and knee osteoarthritis to healthy age-matched controls.

METHODS

Four cohorts (1: knee injury and 2: age-matched controls, and 3: radiographic knee osteoarthritis and 4: age-matched controls) were recruited. Participants performed maximal voluntary isometric knee extensor and flexor contractions. Then, strength (e.g., peak and rate of torque development) and steadiness (e.g., peak power, mean, and median frequency) were derived from each raw torque-time curve and associated power spectral density. A Kruskal-Wallis H test and Spearman's rho correlation analysis assessed cohort differences and association between knee extensor and flexor strength and steadiness.

FINDINGS

The young adult control and knee injury cohorts exhibited greater knee extensor and flexor strength than the older, knee osteoarthritis cohort (p < 0.043). The knee injury cohort, despite being as strong as their healthy counterparts, were significantly less steady with a 92% increase in peak power frequency (p = 0.046). The osteoarthritis cohort exhibited 157% less total power compared to the knee injury and young control cohorts (p < 0.019). Knee extensor and flexor peak torque, rate of torque development, and mean torque exhibit a significant, positive relation with total power (p < 0.018).

INTERPRETATION

Individuals with knee injury and disease may exhibit weaker or less steady knee musculature, predisposing them to degenerative joint disease. Clinicians may need to restore knee extensor and flexor steadiness to facilitate better joint neuromuscular control.

Neural and muscular contributions to the age-related differences in peak power of the knee extensors in men and women

The mechanisms for the loss in limb muscle power output in old (60-79 yr) and very old (≥80 yr) adults and whether the mechanisms differ between men and women are not well understood. We compared maximal peak power of the knee extensor muscles between young, old, and very old men and women and identified the neural and muscular factors contributing to the age-related differences in power. Thirty-one young (22.9 ± 3.0 yr, 15 women), 82 old (70.3 ± 4.9 yr, 38 women), and 16 very old adults (85.8 ± 4.2 yr, 9 women) performed maximal isokinetic contractions at 14 different velocities (30-450°/s) to identify peak power. Voluntary activation (VA) and contractile properties were assessed with transcranial magnetic stimulation to the motor cortex and electrical stimulation of the femoral nerve. The age-related loss in peak power was ∼6.5 W·yr-1 for men (R2 = 0.62, P < 0.001), which was a greater rate of decline (P = 0.002) than the ∼4.2 W·yr-1 for women (R2 = 0.77, P < 0.001). Contractile properties were the most closely associated variables with peak power for both sexes, such as the rate of torque development of the potentiated twitch (men: R2 = 0.69, P < 0.001; women: R2 = 0.57, P < 0.001). VA was weakly associated with power in women (R2 = 0.13, P = 0.012) but not in men (P = 0.191). Similarly, neuromuscular activation [rates of electromyography (EMG) rise] during the maximal power contraction was associated with power in women (R2 = 0.07, P = 0.042) but not in men (P = 0.456). These data suggest that the age-related differences in maximal peak power of the knee extensor muscles are due primarily to factors within the muscle for both sexes, although neural factors may play a minor role in older women.NEW & NOTEWORTHY The greater age-related loss in power relative to the loss in muscle mass of the knee extensors was primarily due to factors altering the contractile properties of the muscle for both old and very old (≥80 yr) adults. The mechanisms for the decrements in power with aging appear largely similar for men and women, although neural factors may play more of a role in older women.

Muscle Torque-Velocity Relationships and Fatigue With Reduced Knee Joint Range of Motion in Young and Older Adults

The purpose of this study was to evaluate the influence of knee joint range of motion (RoM) on the torque-velocity relationship and fatigue in the knee extensor muscles of 7 young (median = 26 y) and 7 older (68 y) adults. Each leg was assigned a RoM (35° or 75°) over which to perform a torque-velocity protocol (maximal isokinetic contractions, 60-300°·s-1) and a fatigue protocol (120 maximal contractions at 120°·s-1, 0.5 Hz). Six older participants were unable to reach 300°·s-1 over 35°. Therefore, the velocity eliciting 75% of peak torque at 60°·s-1 (V75, °·s-1) was calculated for each RoM from a fit of individual torque-velocity curves (60-240°·s-1), and ΔV75 (35°-75°) was determined. Fatigue (final torque/initial torque) was used to calculate Δfatigue (35°-75°). ΔV75 was not different from 0 in young (-28.3°·s-1 [-158.6 to 55.7], median [range], P = .091) or older (-18.5°·s-1 [-95.0 to 23.9], P = .128), with no difference by age (P = .710). In contrast, fatigue was greater for 75° in young (Δfatigue = 25.9% [17.5-30.3], P = .018) and older (17.2% [11.9-52.9], P = .018), with no effect of age (P = .710). These data indicate that, regardless of age, RoM did not alter the torque-velocity relationship between 60 and 240°·s-1, and fatigue was greater with a larger RoM.

The 1-min sit-to-stand test induces a significant and reliable level of neuromuscular fatigability: insights from a mobile app analysis

PURPOSE

The performance metric associated with the execution of the 1-min sit-to-stand (1STS) typically relies on the number repetitions completed in 1 min. This parameter presents certain limitations (e.g., ceiling effect, motivational factors) which can impede its interpretation. Introducing additional parameters, such as neuromuscular fatigability level, could enhance the informative value of the 1STS and facilitate its interpretation. This study aimed to assess (i) whether the 1STS induces fatigability and (ii) the reliability of the fatigability level.

METHODS

Forty young, healthy, and active participants underwent the 1STS twice during the same session. Isolated sit-to-stand maneuvers were performed before, immediately, and 1 min after completing the 1STS. A mobile app was utilized to obtain time (STST), velocity (STSV), and muscle power (STSP) from these sit-to-stand maneuvers. The pre-post change in these parameters served as the fatigability marker. Reliability was assessed using the intra-class correlation coefficient (ICC) and the coefficient of variation (CV).

RESULTS

The mean number of repetitions during the 1STS was 63 ± 9. Significant decline in performance was observed for STST (13 ± 8%), STSV (-11.2 ± 6%), and STSP (-5.2 ± 3%), with more than 74% of participants exhibiting a decline beyond the minimal detectable change. Excellent between-session reliability (ICC ≥ 0.9; CV ≤ 5.3) was observed for the mobile app variables.

CONCLUSION

The 1STS induces significant levels of fatigability. The fatigability indicators derived from the mobile app demonstrated remarkable reliability. Utilizing this user-friendly interface for computing fatigability may empower professionals to acquire insightful complementary indicators from the 1STS.

Walking net V ˙ O2 rises with advancing age in older women: where to go from here?

PURPOSE

Walking net V ˙ O2 tends to increase with advancing age; however, factors contributing to this relationship have not been widely described. The implications of such findings could inform targeted strategies to promote independent mobility in older adults. Herein, we evaluated the relationship between net V ˙ O2 and age at two submaximal workloads while exploring potential moderators of this relationship.

METHODS

Secondary analyses were performed on 35 older (65 ± 3 years) women who completed a battery of physical assessments including fixed-speed, non-graded and graded (+ 2.5%) treadmill walking with indirect calorimetry to determine net V ˙ O2. Maximal oxygen uptake ( V ˙ O2max), knee extensor maximal isometric voluntary contraction (MVC), peak rate of torque development (RTD), and plantar flexor range-of-motion (PFROM) were also measured.

RESULTS

Bivariate correlations showed non-graded (r = 0.403, p = 0.017) and graded (r = 0.413, p = 0.014) net V ˙ O2 were positively related to age. Notably, these relationships strengthened after adjusting for V ˙ O2max. Regression modeling showed age, RTD:MVC ratio (composite of muscle performance), and PFROM together explained 49% and 34% of the variance in non-graded and graded net V ˙ O2, respectively. Further analyses suggested knee extensor MVC moderates the relationship between non-graded net V ˙ O2 and age, accounting for 9% of the variance [ΔR2 = 0.090, F (1,31) = 4.13, p = 0.05].

CONCLUSION

These data support the premise that, in older women, walking net V ˙ O2 rises with advancing age, and additionally, the RTD:MVC ratio and PFROM are independent correlates of non-graded net V ˙ O2. Exercise interventions with a high degree of training specificity including explosive, velocity-based elements may promote independent mobility in older women.

Effects of Combined Endurance and Resistance Eccentric Training on Muscle Function and Functional Performance in Patients With Chronic Obstructive Pulmonary Disease: Randomized Controlled Trial

OBJECTIVE

To evaluate the adherence to treatment and efficacy of an eccentric-based training (ECC) program on peripheral muscle function and functional exercise capacity in patients with chronic obstructive pulmonary disease (COPD).

DESIGN

Prospective, assessor-blinded, randomized controlled trial.

SETTING

The cardiopulmonary rehabilitation unit of a tertiary subacute referral center.

PARTICIPANTS

Thirty (N=30) stable inpatients (mean age 68±8 years; FEV1 44±18% of predicted) with COPD were included in the study.

INTERVENTIONS

Inpatients were randomly assigned to 4 weeks of a combined endurance and resistance ECC (n=15) or conventional training (CON; n=15).

MAIN OUTCOME MEASURES

Quadriceps peak torque (PT) was the primary outcome measure for muscle function. Rate of force development (RFD), muscle activation and quality (quadriceps PT/leg lean mass), 6-min walk distance (6MWD), 4-meter gait speed (4mGS), 10-meter gait speed, 5-repetition sit-to-stand (5STS), dyspnea rate, and mortality risk were the secondary outcomes. Evaluations were performed at baseline and repeated after 4 weeks and 3 months of follow-up.

RESULTS

Quadriceps PT, RFD, and muscle quality improved by 17±23% (P<.001), 19±24%, and 16±20% (both P<.05) within the ECC group. Besides, a significant between-group difference for RFD (56±94 Nm/s, P=.038) was found after training. Both groups showed clinically relevant improvements in 6MWD, 4mGS, dyspnea rate, and mortality risk, with no significant differences between groups.

CONCLUSION

Combined endurance and resistance ECC improved lower limbs muscle function compared with CON in inpatients with COPD. In contrast, ECC did not further improve functional performance, dyspnea, and mortality risk. ECC may be of particular benefit to effect on skeletal muscle function in patients with COPD.

Muscle fatigue, bioenergetic responses and metabolic economy during load- and velocity-based maximal dynamic contractions in young and older adults

We evaluated whether task-dependent, age-related differences in muscle fatigue (contraction-induced decline in normalized power) develop from differences in bioenergetics or metabolic economy (ME; mass-normalized work/mM ATP). We used magnetic resonance spectroscopy to quantify intracellular metabolites in vastus lateralis muscle of 10 young and 10 older adults during two maximal-effort, 4-min isotonic (20% maximal torque) and isokinetic (120°s-1 ) contraction protocols. Fatigue, inorganic phosphate (Pi), and pH (p ≥ 0.213) differed by age during isotonic contractions. However, older had less fatigue (p ≤ 0.011) and metabolic perturbation (lower [Pi], greater pH; p ≤ 0.031) than young during isokinetic contractions. ME was lower in older than young during isotonic contractions (p ≤ 0.003), but not associated with fatigue in either protocol or group. Rather, fatigue during both tasks was linearly related to changes in [H+ ], in both groups. The slope of fatigue versus [H+ ] was 50% lower in older than young during isokinetic contractions (p ≤ 0.023), consistent with less fatigue in older during this protocol. Overall, regardless of age or task type, acidosis, but not ME, was the primary mechanism for fatigue in vivo. The source of the age-related differences in contraction-induced acidosis in vivo remains to be determined, as does the apparent task-dependent difference in the sensitivity of muscle to [H+ ].

Neural and muscular contributions to the age-related loss in power of the knee extensors in men and women

The mechanisms for the loss in limb muscle power in old (60-79 years) and very old (≥80 years) adults and whether the mechanisms differ between men and women are not well-understood. We compared maximal power of the knee extensor muscles between young, old, and very old men and women and identified the neural and muscular factors contributing to the age-related loss of power. 31 young (22.9±3.0 years, 15 women), 83 old (70.4±4.9 years, 39 women), and 16 very old adults (85.8±4.2 years, 9 women) performed maximal isokinetic contractions at 14 different velocities (30-450°/s) to identify peak power. Voluntary activation (VA) and contractile properties were assessed with transcranial magnetic stimulation to the motor cortex and electrical stimulation of the femoral nerve. The age-related loss in power was ~6.5 W·year-1 for men (R2=0.62, p<0.001), which was a greater rate of decline (p=0.002) than the ~4.2 W·year-1 for women (R2=0.77, p<0.001). Contractile properties were the most closely associated variables with power output for both sexes, such as the rate of torque development of the potentiated twitch (men: R2=0.69, p<0.001; women: R2=0.57, p<0.001). VA was weakly associated with power in women (R2=0.13, p=0.012) but not men (p=0.191), whereas neuromuscular activation (EMG amplitude) during the maximal power contraction was not associated with power in men (p=0.347) or women (p=0.106). These data suggest that the age-related loss in power of the knee extensor muscles is due primarily to factors within the muscle for both sexes, although neural factors may play a minor role in older women.

High-velocity power training has similar effects to traditional resistance training for functional performance in older adults: a systematic review

QUESTIONS

What is the effect of high-velocity power training (HVPT) compared with traditional resistance training (TRT) on functional performance in older adults? What is the quality of intervention reporting for the relevant literature?

DESIGN

Systematic review and meta-analysis of randomised controlled trials.

PARTICIPANTS

Older adults (aged > 60 years), regardless of health status, baseline functional capacity or residential status.

INTERVENTIONS

High-velocity power training with the intent to perform the concentric phase as quickly as possible compared with traditional moderate-velocity resistance training performed with a concentric phase of ≥ 2 seconds.

OUTCOME MEASURES

Short Physical Performance Battery (SPPB), Timed Up and Go test (TUG), five times sit-to-stand test (5-STS), 30-second sit-to-stand test (30-STS), gait speed tests, static or dynamic balance tests, stair climb tests and walking tests for distance. The quality of intervention reporting was assessed with the Consensus on Exercise Reporting Template (CERT) score.

RESULTS

Nineteen trials with 1,055 participants were included in the meta-analysis. Compared with TRT, HVPT had a weak-to-moderate effect on change from baseline scores for the SPPB (SMD 0.27, 95% CI 0.02 to 0.53; low-quality evidence) and TUG (SMD 0.35, 95% CI 0.06 to 0.63; low-quality evidence). The effect of HVPT relative to TRT for other outcomes remained very uncertain. The average CERT score across all trials was 53%, with two trials rated high quality and four rated moderate quality.

CONCLUSION

HVPT had similar effects to TRT for functional performance in older adults, but there is considerable uncertainty in most estimates. HVPT had better effects on the SPPB and TUG, but it is unclear whether the benefit is large enough to be clinically worthwhile.

Effects of Visual Input Absence on Balance Recovery Responses to Lateral Standing Surface Perturbations in Older and Younger Adults

Although the ability to recover balance in the lateral direction has important implications with regard to fall risk in older adults, the effect of visual input on balance recovery in response to lateral perturbation and the effect of age are not well studied. We investigated the effect of visual input on balance recovery response to unpredictable lateral surface perturbations and its age-related changes. Ten younger and 10 older healthy adults were compared during balance recovery trials performed with the eyes open and eyes closed (EC). Compared with younger adults, older adults showed increased electromyography (EMG) peak amplitude of the soleus and gluteus medius, reduced EMG burst duration of the gluteus maximus and medius, and increased body sway (SD of the body's center of mass acceleration) in EC. In addition, older adults exhibited a smaller % increase (EC-eyes open) of the ankle eversion angle, hip abduction torque, EMG burst duration of the fibularis longus, and a greater % increase of body sway. All kinematics, kinetics, and EMG variables were greater in EC compared with eyes open in both groups. In conclusion, the absence of visual input negatively affects the balance recovery mechanism more in older adults compared with younger adults.

The interactions between agonist-to-antagonist muscle strength performance and plantar pressure distribution, foot contact area, and impulse in novice ballet dancers

BACKGROUND

Hip, trunk, knee, and ankle/foot muscles may lead to increased variability in the components of balance and plantar pressure distribution (PPD) analysis. However, the role of these muscle groups in the PPD of different ballet techniques in novice ballet dancers has not previously been studied.

OBJECTIVE

Our objective was to examine whether balance and PPD vary among five different ballet techniques and correlate with the agonist-to-antagonist strength performance of trunk, knee, hip, and ankle muscles in adolescent ballet dancers.

METHODS

The anthropometric parameters, muscle strength performance, balance, and PPD of sixty healthy female ballet dancers (age: 14.36 ± 2.18 y) were measured at 48-h intervals.

RESULTS

The forefoot's PPD was significantly greater than the midfoot and rearfoot for all techniques (p= 0.000). The percent plantar load of forefoot during développé à la seconde (side, front, back), passé, and penché was greater than midfoot (166.56%, 161.51%, 168.11%, 165.14%, 174.04%) and rearfoot (47.75%, 32.84%, 43.83%, 48.73%, 49.66) for all techniques, respectively. The forefoot's PPD, impulse, and contact area during all techniques were significantly correlated with the trunk muscle strength ratio (p< 0.05).

CONCLUSION

Ballet dancers with higher trunk muscle strength imbalance showed a greater percentage difference in pressure load between the left and right foot in the anterior and posterior directions, poor balance, aggravated trunk imbalance, increased PPD, contact area, and impulse in the forefoot during each technique.

Differences in the Relationships Between Muscle Strength, Muscle Mass, Balance Function, and Quality of Life for Middle-Aged and Older Breast Cancer Survivors

PURPOSE

The purpose of this study was to investigate the differences in muscle strength, muscle mass, balance function, and quality of life (QOL) among middle-aged breast cancer survivors (BCSs) and older BCSs.

METHODS

The study included 53 middle-aged (<65 years old) BCSs and 49 older (≥65 years old) BCSs. Muscle strength was evaluated via handgrip and knee extensor strength, and muscle mass was assessed using a body composition test. Balance function was assessed using the Timed Up and Go test and the body sway test. QOL was assessed using the Medical Outcome Study 36-item Short-Form Health Survey.

RESULTS

The older BCSs had significantly lower right grip strength, right knee extension strength, and muscle mass (P < .05) than the middle-aged BCSs. In addition, the body sway test showed that older BCSs had a significant increase in the length of center of pressure compared to middle-aged BCSs (P < .05). Older BCSs showed significantly lower physical functioning subscales in QOL compared to middle-aged BCSs (P < .05). The associations among muscle strength, muscle mass and QOL were more significantly observed in the older BCSs (P < .05). Furthermore, a significant correlation between QOL and balance function was observed in the older BCSs, but not in the middle-aged BCSs (P < .05).

CONCLUSION

There may be associations among muscle strength, muscle mass, balance and QOL in older BCSs, but not in middle-aged BCSs. We believe that the findings of this study will be relevant in the context of planning rehabilitation for older BCSs.

Muscle function and functional performance after pulmonary rehabilitation in patients with chronic obstructive pulmonary disease: a prospective observational study

This study aimed to measure changes in different properties of skeletal muscles and evaluate their contribution and relationship to changes in functional performance after pulmonary rehabilitation (PR) in patients with chronic obstructive pulmonary disease (COPD). COPD outpatients attending 5 weeks of conventional PR were recruited. Functional performance [5-repetitions sit-to-stand (5STS), and 4-m gait speed (4mGS)], and muscle function (maximal isometric strength, power, force control, and relative concentric and eccentric activation during 5STS) were assessed after PR and 3 months of follow-up. Twenty patients (71 years; 52% of predicted FEV₁) completed the study. 4mGS and relative concentric activation during 5STS decreased respectively by 7.7% and 26% between the beginning of PR and follow-up. Quadriceps strength, power, and force control improved by 10.4%, 27.3%, and 15.2%, respectively, from the beginning of PR to follow-up the relative eccentric activation during 5STS explained 31% of the variance in 4mGS changes. In conclusion, functional performance appeared to decline after conventional PR, whereas several properties of skeletal muscles were maintained at follow-up in COPD outpatients. Of note, eccentric contractions might play a role in the improvement of functional performance. Therefore, future studies with interventional design should include eccentric training in PR programs during clinical COPD practice.

Acute Responses to Resistance Training on Body Composition, Muscular Fitness and Flexibility by Sex and Age in Healthy War Veterans Aged 50-80 Years

Background: Although evidence suggests that resistance training should be prescribed as a method to enhance or maintain physical fitness, these findings are mostly based on research on younger men. Studies investigating responses by sex and age to resistance training, especially in war veterans aged ≥50 years, are lacking. Therefore, the main purpose of this study was to examine whether a 4-week resistance training program would have similar effects on body composition, muscular fitness, and flexibility in men and women aged 50−80 years. Methods: Seven-hundred and sixty-four participants were recruited and categorized into two groups each of men and women aged 50−64 and 65−80 years. The training intervention lasted 4 weeks and consisted of three 60 min sessions per week. All participants were tested for each of the following physical fitness components: body composition, push-ups in 30 s, chair-stands in 30 s, sit-ups in 30 s, and a sit-and-reach test. Results: Over the intervention period of 4 weeks, body weight (p = 0.002) and the percent of fat mass (p < 0.001) decreased, while the percent of lean mass (p < 0.001) in push-ups in 30 s (p < 0.001), chair-stands in 30 s (p < 0.001), sit-ups in 30 s (p < 0.001), and sit-and-reach (p < 0.001) increased. Significant time*age interactions were shown for push-ups in 30 s (F1,763 = 4.348, p = 0.038) and chair-stands in 30 s (F1,763 = 9.552, p = 0.002), where men and women aged 50−64 years exhibited larger time-induced changes compared to their older (65−80 yr) counterparts. Effect sizes were similar between sex- and age-specific groups. Conclusions: The 4-week resistance training produced similar pronounced positive effects on body composition, muscular fitness, and flexibility, while men and women aged 50−64 years displayed significantly larger improvements in upper and lower muscular fitness compared with their 65−80-year-old counterparts.

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.

Perturbation-Induced Protective Arm Responses: Effect of Age, Perturbation-Intensity, and Relationship with Stepping Stability: A Pilot Study

During balance recovery from slip perturbations, forward flexion (elevation) of the arms serves to counterbalance the posteriorly displaced center of mass (CoM). We aimed to investigate whether aging affects modulation of arm responses to various intensities of unpredictable slip perturbations and whether arm responses are related to compensatory stepping stability. Ten healthy young adults and ten healthy older adults participated. Participants were asked to react naturally to three randomly administered levels of slip-like surface perturbations (intensity 1 (7.75 m/s2), intensity 2 (12.00 m/s2) and intensity 3 (16.75 m/s2), which occurred by means of forward acceleration of the treadmill belt while standing. Kinematic data were collected using a motion capture system. Outcomes included arm elevation displacement, velocity, and margin of stability (MoS) of compensatory stepping. The results reveal no modulation of arm elevation velocity in older adults from perturbation intensity 1 to 2, whereas younger adults demonstrated progressive increases from intensity 1 to 2 to 3. At intensity 3, older adults demonstrated reduced maximal arm elevation velocity compared to younger adults (p = 0.02). The results in both groups combined reveal a positive correlation between maximal arm elevation velocity and first compensatory step MoS at intensity 3 (p = 0.01). Together, these findings indicate age-related decreases in arm response modulation and the association of arm elevation response with protective stepping stability, suggesting that fall prevention interventions may benefit from an emphasis on arm elevation velocity control in response to greater perturbation intensities.

Comparison of Azure Kinect and optical retroreflective motion capture for kinematic and spatiotemporal evaluation of the sit-to-stand test

BACKGROUND

The sit-to-stand test (STS) is commonly used to evaluate functional capabilities within a variety of clinical populations. Traditionally STS is a timed test, limiting the depth of information which can be gained from its evaluation. The Azure Kinect has the potential to add in-depth analysis to STS. Despite these potential benefits, the recently released (2019) Azure Kinect has yet to be evaluated for its ability to accurately assess STS.

RESEARCH QUESTIONS

Purposes of this work were to compare data captured during STS using both a 12 camera Vicon motion capture system and the Azure Kinect; and to calculate kinematic and spatiotemporal variables related to the four phases of the STS cycle.

METHODS

Spatiotemporal and kinematic measures for STS were simultaneously collected by both devices for 15 participants. Cycle waveforms were compared for right and left hip and knee flexion/extension angular displacement, right and left hip and knee flexion/extension angular velocity, and knee-to-ankle separation ratio. Evaluated discrete outcome variables included: phase time points, maximum knee extension velocity from phases 3 to 4, medial-lateral pelvic sway range, and total time to completion. Waveform summary data were compared using R, R², and RMSE. Discrete variables were analyzed using Spearman's Rank correlation coefficient.

RESULTS

R and R² values between the two systems indicated high levels of correlation (all R values > 0.711, all R² values > 0.660). Although there was an overall high level of agreement between waveform shapes, high RMSE values indicated some minor tracking errors for Kinect within the STS cycle. Spearman's Rank correlation coefficient indicated high levels of correlation between the systems for discrete variables (all R values > 0.89), with the exception of medial-lateral pelvic sway range.

SIGNIFICANCE

The Azure Kinect provides valuable insight into STS movement strategies allowing for improved precision in clinical decision making across multiple clinical populations.

Perioperative assessment of muscle inflammation susceptibility in patients with end-stage osteoarthritis

Many individuals with end-stage osteoarthritis (OA) undergo elective total hip/knee arthroplasty (THA/TKA) to relieve pain, improve mobility and quality of life. However, ∼30% suffer long-term mobility impairment following surgery. This may be in part due to muscle inflammation susceptibility (MuIS+), an overt proinflammatory pathology localized to skeletal muscle surrounding the diseased joint, present in some patients with TKA/THA. We interrogated the hypothesis that MuIS+ status results in a perturbed perioperative gene expression profile and decreases skeletal muscle integrity in patients with end-stage OA. Samples were leveraged from the two-site, randomized, controlled trial R01HD084124, NCT02628795. Participants were dichotomized based on surgical (SX) muscle gene expression of TNFRSF1A (TNF-αR). MuIS+/- samples were probed for gene expression and fibrosis. Paired and independent two-tailed t tests were used to determine differences between contralateral (CTRL) and surgical (SX) limbs and between-subject comparisons, respectively. Significance was declared at P < 0.05. Seventy participants (26M/44F; mean age 62.41 ± 8.86 yr; mean body mass index 31.10 ± 4.91 kg/m2) undergoing THA/TKA were clustered as MuIS+ (n = 24) or MuIS- (n = 46). Lower skeletal muscle integrity (greater fibrosis) exists on the SX versus CTRL limb (P < 0.001). Furthermore, MuIS+ versus MuIS- muscle exhibited higher proinflammatory (IL-6R and TNF-α) and catabolic (TRIM63) gene expression (P < 0.001, P = 0.004, and 0.024 respectively), with a trend for greater fibrosis (P = 0.087). Patients with MuIS+ exhibit more inflammation and catabolic gene expression in skeletal muscle of the SX limb, accompanied by decreased skeletal muscle integrity (Trend). This highlights the impact of MuIS+ status emphasizing the potential value of perioperative MuIS assessment to inform optimal postsurgical care.NEW & NOTEWORTHY This study assessed the skeletal muscle molecular characteristics associated with end-stage osteoarthritis and refined an important phenotype, in some patients, termed muscle inflammation susceptibility (MuIS+) that may be an important consideration following surgery. Furthermore, we provide evidence of differential inflammatory and catabolic gene expression between the contralateral and surgical limbs along with differences between the skeletal muscle surrounding the diseased hip versus knee joints.

Longevity interventions temporally scale healthspan in Caenorhabditis elegans

Human centenarians and longevity mutants of model organisms show lower incidence rates of late-life morbidities than the average population. However, whether longevity is caused by a compression of the portion of life spent in a state of morbidity, i.e., "sickspan," is highly debated even in isogenic Caenorhabditis elegans. Here, we developed a microfluidic device that employs acoustophoretic force fields to quantify the maximum muscle strength and dynamic power in aging C. elegans. Together with different biomarkers for healthspan, we found a stochastic onset of morbidity, starting with a decline in dynamic muscle power and structural integrity, culminating in frailty. Surprisingly, we did not observe a compression of sickspan in longevity mutants but instead observed a temporal scaling of healthspan. Given the conservation of these longevity interventions, this raises the question of whether the healthspan of mammalian longevity interventions is also temporally scaled.

The clinical correlates of the chair sit to stand performance in people with multiple sclerosis

Objective: This study aimed to evaluate the motor and non-motor factors associated with sit-to-stand performance in people with Multiple Sclerosis (PwMS). Design: Observational cross-sectional study. Subjects: A total of 88 individuals with MS participated in this study. Main Measures: Standing performance was measured using the five-times-sit-to-stand test (FTSTS). The Berg Balance Scale to assess balance, the 10-Meter Walking Test (10-MWT) was used to assess walking speed; the Patient Determined Disease Steps (PDDS) was used to assess disability level. Furthermore, Brief International Cognitive Assessment for MS (BICAMS) was used to assess cognitive status, Hospital Anxiety and Depression scale (HADS) to assess depression and anxiety, and the Modified Fatigue Impact scale (MFIS) to evaluate fatigue. Spearman correlation coefficient was used to determine the relationship between all these variables and the FTSTS. Furthermore, multiple linear regression was conducted to determine predictive factors of the FTSTS. Results: FTSTS score was correlated significantly with BBS, PDDS, BICAMS, 10-MWT and MFIS (r ranged from 0.3 to 0.52; P < .05). However, there was no significant correlation observed between the FTSTS and HADS-depression or HADS-anxiety. Considering the multiple regression analysis, the following factors were significantly predictive of the FTSTS: 10-MWT, MFIS and the BICAMS-z score (R²: 0.433, P < .0001). Conclusion: The study concludes that sit to stand is multifactorial and is potentially associated with walking speed, cognitive function and fatigue. These factors should be considered by healthcare professionals in interpreting the sit-to-stand performance of PwMS and in designing rehabilitation interventions.

Older Compared With Younger Adults Performed 467 Fewer Sit-to-Stand Trials, Accompanied by Small Changes in Muscle Activation and Voluntary Force

Background: Repetitive sit-to-stand (rSTS) is a fatigue perturbation model to examine the age-effects on adaptability in posture and gait, yet the age-effects on muscle activation during rSTS per se are unclear. We examined the effects of age and exhaustive rSTS on muscle activation magnitude, onset, and duration during ascent and descent phases of the STS task.

Methods: Healthy older (n = 12) and younger (n = 11) adults performed rSTS, at a controlled frequency dictated by a metronome (2 s for cycle), to failure or for 30 min. We assessed muscle activation magnitude, onset, and duration of plantar flexors, dorsiflexors, knee flexors, knee extensors, and hip stabilizers during the initial and late stages of rSTS. Before and after rSTS, we measured maximal voluntary isometric knee extension force, and rate of perceived exertion, which was also recorded during rSTS task.

Results: Older vs. younger adults generated 35% lower maximum voluntary isometric knee extension force. During the initial stage of rSTS, older vs. younger adults activated the dorsiflexor 60% higher, all 5 muscle groups 37% longer, and the hip stabilizers 80% earlier. Older vs. younger adults completed 467 fewer STS trials and, at failure, their rate of perceived exertion was ~17 of 20 on the Borg scale. At the end of the rSTS, maximum voluntary isometric knee extension force decreased 16% similarly in older and younger, as well as the similar age groups decline in activation of the dorsiflexor and knee extensor muscles (all p < 0.05).

Conclusion: By performing 467 fewer STS trials, older adults minimized the potential effects of fatigability on muscle activation, voluntary force, and motor function. Such a sparing effect may explain the minimal changes in gait after rSTS reported in previous studies, suggesting a limited scope of this perturbation model to probe age-effects on muscle adaptation in functional tasks.

Effects of old age and contraction mode on knee extensor muscle ATP flux and metabolic economy in vivo

KEY POINTS

We used 31-phosphorus magnetic resonance spectroscopy to quantify in vivo skeletal muscle metabolic economy (ME; mass-normalized torque or power produced per ATP consumed) during three 24 s maximal-effort contraction protocols: (1) sustained isometric (MVIC), (2) intermittent isokinetic (MVDC_IsoK ), and (3) intermittent isotonic (MVDC_IsoT ) in the knee extensor muscles of young and older adults. ME was not different between groups during the MVIC but was lower in older than young adults during both dynamic contraction protocols. These results are consistent with an increased energy cost of locomotion, but not postural support, with age. The effects of old age on ME were not due to age-related changes in muscle oxidative capacity or ATP flux. Specific power was lower in older than young adults, despite similar total ATP synthesis between groups. Together, this suggests a dissociation between cross-bridge activity and ATP utilization with age.

ABSTRACT

Muscle metabolic economy (ME; mass-normalized torque or power produced per ATP consumed) is similar in young and older adults during some isometric contractions, but less is known about potential age-related differences in ME during dynamic contractions. We hypothesized that age-related differences in ME would exist only during dynamic contractions, due to the increased energetic demand of dynamic versus isometric contractions. Ten young (Y; 27.5 ± 3.9 years, 6 men) and 10 older (O; 71 ± 5 years, 5 men) healthy adults performed three 24 s bouts of maximal contractions: (1) sustained isometric (MVIC), (2) isokinetic (120°·s^-1 , MVDC_IsoK ; 0.5 Hz), and (3) isotonic (load = 20% MVIC, MVDC_IsoT ; 0.5 Hz). Phosphorus magnetic resonance spectroscopy of the vastus lateralis muscle was used to calculate ATP flux (mM ATP·s^-1 ) through the creatine kinase reaction, glycolysis and oxidative phosphorylation. Quadriceps contractile volume (cm³ ) was measured by MRI. ME was calculated using the torque-time integral (MVIC) or power-time integral (MVDC_IsoK and MVDC_IsoT ), total ATP synthesis and contractile volume. As hypothesized, ME was not different between Y and O during the MVIC (0.12 ± 0.03 vs. 0.12 ± 0.02 Nm^. s^. cm^{-3 .} mM ATP^-1 , mean ± SD, respectively; P = 0.847). However, during both MVDC_IsoK and MVDC_IsoT , ME was lower in O than Y adults (MVDC_IsoK : 0.011 ± 0.003 vs. 0.007 ± 0.002 J^. cm^{-3 .} mM ATP^-1 ; P < 0.001; MVDC_IsoT : 0.011 ± 0.002 vs. 0.008 ± 0.002; P = 0.037, respectively), despite similar muscle oxidative capacity, oxidative and total ATP flux in both groups. The lower specific power in older than young adults, despite similar total ATP synthesis between groups, suggests there is a dissociation between cross-bridge activity and ATP utilization with age.

Functional performance of older adults: A comparison between men and women

The objective of this study was to compare the functional performance of community-dwelling older adults of both sexes and investigate the possible mediation aspects that may influence the sex differences regarding socioeconomic and anthropometric characteristics, health status, and quadriceps muscle strength. 233 Brazilian older adults were assessed, and men's and women's sociodemographic data, physical activity level, quadriceps muscle strength, functional performance (gait speed and the SPPB), and history of falls were compared. Sex differences in functional performance were observed even after statistically adjusting the model (age, body mass, income, physical activity level, and occurrence of falls). When quadriceps muscle strength was included in the adjusted model, the sex difference remained only for gait speed. When stature was included in the adjusted model, the sex difference in gait speed disappeared. Our results suggest that the sex difference in functional performance assessed by the SPPB can be explained due to the fact that men are stronger than women. In addition, the sex difference regarding gait speed was explained by the sex difference in stature. Public actions that encourage older women to practice physical activities that promote increased muscle strength can positively interfere with their best functional performance for as long as possible.

Responses to Maximal Strength Training in Different Age and Gender Groups

Purpose

The present study aimed to investigate the potential impact of age, gender, baseline strength, and selected candidate polymorphisms on maximal strength training (MST) adaptations.

Methods

A total of 49 subjects (22 men and 27 women) aged 20–76 years, divided into five age groups, completed an 8 weeks MST intervention. Each MST session consisted of 4 sets with 4 repetitions at ∼85–90% of one-repetition maximum (1RM) intensity in leg-press, three times per week. 1RM was tested pre and post the intervention and blood samples were drawn to genotype candidate polymorphisms ACE I/D (rs1799752), ACTN3 R577X (rs1815739), and PPARGC1A Gly482Ser (rs8192678).

Results

All age groups increased leg-press 1RM (p < 0.01), with a mean improvement of 24.2 ± 14.0%. There were no differences in improvements between the five age groups or between male and female participants, and there were no non-responders. Baseline strength status did not correlate with 1RM improvements. PPARGC1A rs8192678 T allele carriers had a 15% higher age- and gender corrected baseline 1RM than the CC genotype (p < 0.05). C allele carriers improved 1RM (%) by 34.2% more than homozygotes for the T allele (p < 0.05).

Conclusion

To the best of our knowledge, this is the first study to report improvement in leg-press maximal strength regardless of gender, baseline strength status in all age groups. The present study is also first to demonstrate an association between the PPARGC1A rs8192678 and maximal strength and its trainability in a moderately trained cohort. MST may be beneficial for good health and performance of all healthy individuals.

Associations of muscle lipid content with physical function and resistance training outcomes in older adults: altered responses with metformin

Preserving muscle mass and strength is critical for long-term health and longevity. Age-related muscle lipid accumulation has been shown to be detrimental to muscle health. In healthy older individuals, we sought to determine whether muscle lipid content, determined from computed tomography, is associated with self-reported physical function, laboratory-measured performance, and the response to progressive resistance training (PRT), and how metformin may alter these responses (N = 46 placebo, 48 metformin). Using multiple linear regression models adjusted for confounders in a large cohort, we show that intermuscular adipose tissue (IMAT) was not associated with baseline function or response to PRT, contrary to previous reports. On the other hand, thigh muscle density (TMD), as an indicator of intra- and extramyocellular lipid (IMCL and EMCL), remained strongly and independently positively associated with physical function and performance following adjustment. Baseline TMD was inversely associated with gains in strength, independent of muscle mass. Percent change in TMD was positively associated with improved chair stand and increased type II fiber frequency but was not associated with muscle hypertrophy or overall strength gain following PRT. For the first time, we show that metformin use during PRT blunted density and strength gains by inhibiting fiber type switching primarily in those with low baseline TMD. These results indicate that participants with higher muscle lipid content derive the most performance benefit from PRT. Our results further indicate that muscle density may be as influential as muscle size for strength, physical function, and performance in healthy older adults. ClinicalTrials.gov , NCT02308228, Registered on 25 November 2014.

ISB clinical biomechanics award winner 2019: Knee extensor fatigue resistance in individuals following anterior cruciate ligament reconstruction

BACKGROUND

Individuals following anterior cruciate ligament reconstruction demonstrate quadriceps weakness throughout the post-operative recovery and at the time of returning to sport. This is often accompanied with patterns of quadriceps fatigue resistance. As such, fatigue may be an identifier of individuals with delayed recovery. The purpose was to assess quadriceps fatigue in anterior cruciate ligament reconstructed patients at the time of return to sport in comparison to healthy controls.

METHODS

A total of 215 individuals, 120 following anterior cruciate ligament reconstruction (21.0 (2.9) years, 63 Female, 5.96 (0.48) months post-surgery) and 95 healthy controls (21.5 (8.4) years, 49 Female), participated in this study. All participants completed a 30-s knee extensor maximum voluntary isometric contraction. Knee extensor strength, limb symmetry index, and fatigue (%) were compared between groups. Between-limb fatigue comparisons were made through the Fatigue Index Limb Difference = [(Involved Limb Fatigue Index) - (Uninvolved Limb Fatigue Index)].

FINDINGS

Individuals following anterior cruciate ligament reconstruction (18.7 (10.9)%, -5.6 (11.2)) demonstrated lower values of unilateral fatigue and Fatigue Index Limb Difference compared to healthy participants (22.5 (8.2)%, P = .002; 2.2 (7.9), P < .001). For anterior cruciate ligament reconstructed patients, there was a weak, negative, significant relationship between the involved limb strength and fatigue (r = -0.184, P = .048). There was no relationship between limb symmetry and Fatigue Index Limb Difference (r = 0.137, P = .142). For Healthy individuals, there was a positive, moderate relationship between limb symmetry and Fatigue Index Limb Difference (r = 0.400, P < .001).

INTERPRETATION

Individuals following anterior cruciate ligament reconstruction demonstrate fatigue resistance compared to healthy active controls and greater resistance to fatigue in their involved limb compared to their contralateral limb.

Aging and Recovery After Resistance-Exercise-Induced Muscle Damage: Current Evidence and Implications for Future Research

Aging is anecdotally associated with a prolonged recovery from resistance training, though current literature remains equivocal. This brief review considers the effects of resistance training on indirect markers of muscle damage and recovery (i.e., muscle soreness, blood markers, and muscle strength) in older males. With no date restrictions, four databases were searched for articles relating to aging, muscle damage, and recovery. Data from 11 studies were extracted for review. Of these, four reported worse symptoms in older compared with younger populations, while two have observed the opposite, and the remaining studies (n = 6) proposed no differences between age groups. It appears that resistance training can be practiced in older populations without concern for impaired recovery. To improve current knowledge, researchers are urged to utilize more ecologically valid muscle-damaging bouts and investigate the mechanisms which underpin the recovery of muscle soreness and strength after exercise in older populations.

Muscle architecture, voluntary activation, and low-frequency fatigue do not explain the greater fatigue of older compared with young women during high-velocity contractions

Although high-velocity contractions elicit greater muscle fatigue in older than young adults, the cause of this difference is unclear. We examined the potential roles of resting muscle architecture and baseline contractile properties, as well as changes in voluntary activation and low-frequency fatigue in response to high-velocity knee extensor work. Vastus lateralis muscle architecture was determined in quiescent muscle by ultrasonography in 8 young (23.4±1.8 yrs) and 8 older women (69.6±1.1). Maximal voluntary dynamic (MVDC) and isometric (MVIC), and stimulated (80Hz and 10Hz, 500ms) isometric contractions were performed before and immediately after 120 MVDCs (240°.s-1, one every 2s). Architecture variables did not differ between groups (p≥0.209), but the half-time of torque relaxation (T1/2) was longer in older than young women at baseline (151.9±6.0 vs. 118.8±4.4 ms, respectively, p = 0.001). Older women fatigued more than young (to 33.6±4.7% vs. 55.2±4.2% initial torque, respectively; p = 0.004), with no evidence of voluntary activation failure (ΔMVIC:80Hz torque) in either group (p≥0.317). Low-frequency fatigue (Δ10:80Hz torque) occurred in both groups (p<0.001), as did slowing of T1/2 (p = 0.001), with no differences between groups. Baseline T1/2 was inversely associated with fatigue in older (r2 = 0.584, p = 0.045), but not young women (r2 = 0.147, p = 0.348). These results indicate that differences in muscle architecture, voluntary activation, and low-frequency fatigue do not explain the greater fatigue of older compared with young women during high-velocity contractions. The inverse association between baseline T1/2 and fatigue in older women suggests that factors related to slower muscle contractile properties may be protective against fatigue during fast, repetitive contractions in aging.

Muscle Power is Related to Physical Function in Patients Surviving Acute Respiratory Failure: A Prospective Observational Study

BACKGROUND

Up to 66% of patients admitted to the intensive care unit (ICU) for acute respiratory failure (ARF) develop ICU-acquired weakness, which is diagnosed by muscle strength testing. Muscle power, different from strength, is an important determinant of function that is not a common focus in patients surviving critical illness. Therefore, the purpose of this study is to assess muscle power in survivors of ARF.

METHODS

A cross-sectional observational study performed with survivors of ARF. Muscle power, strength and physical function were assessed 4-8 weeks post-hospital discharge. Cross sectional area and echogenicity of rectus femoris and tibialis anterior muscles were assessed using ultrasonography. Healthy community-dwelling adults were included for comparison.

RESULTS

12 survivors of ARF mean age of 55.6 ± 17.1 (66% male) and 12 healthy adults mean age of 51.6.1 ± 10.3 (66% male) participated in this study. Patients in the post-ARF group had a mean muscle power of 9.9 ± 3.5 W and 63.7 ± 31.6 W for 2-lb and 10% of body-weight loads, respectively. Compared to matched controls, power in ARF group was reduced by 43%. Muscle power in post-ARF group had moderate correlations with 5-times sit-to-stand testing (r = -0.644, P = 0.024), 4-m habitual gait speed (-0.780, P = 0.002), and 6-min walk distance (r = 0.589, P = 0.044).

CONCLUSIONS

Muscle power is significantly reduced in survivors of critical illness and associated with deficits in physical function. These preliminary findings may support therapeutic interventions aimed at improving muscle power to potentially increase functional benefit.

Age-specific modulation of intermuscular beta coherence during gait before and after experimentally induced fatigue

We examined the effects of age on intermuscular beta-band (15-35 Hz) coherence during treadmill walking before and after experimentally induced fatigue. Older (n = 12) and younger (n = 12) adults walked on a treadmill at 1.2 m/s for 3 min before and after repetitive sit-to-stand, rSTS, to induce muscle fatigability. We measured stride outcomes and coherence from 100 steps in the dominant leg for the synergistic (biceps femoris (BF)-semitendinosus, rectus femoris (RF)-vastus lateralis (VL), gastrocnemius lateralis (GL)-Soleus (SL), tibialis anterior (TA)-peroneus longus (PL)) and for the antagonistic (RF-BF and TA-GL) muscle pairs at late swing and early stance. Older vs. younger adults had 43-62% lower GL-SL, RF-VL coherence in swing and TA-PL and RF-VL coherence in stance. After rSTS, RF-BF coherence in late swing decreased by ~ 20% and TA-PL increased by 16% independent of age (p = 0.02). Also, GL-SL coherence decreased by ~ 23% and increased by ~ 23% in younger and older, respectively. Age affects the oscillatory coupling between synergistic muscle pairs, delivered presumably via corticospinal tracts, during treadmill walking. Muscle fatigability elicits age-specific changes in the common fluctuations in muscle activity, which could be interpreted as a compensation for muscle fatigability to maintain gait performance.

A Fully Soft and Passive Assistive Device to Lower the Metabolic Cost of Sit-to-Stand

Various assistive devices like exoskeletons have been developed to aid the growing number of disabled people. Recent studies have started to explore using soft rather than rigid components to create lightweight and unobtrusive systems that can be more easily adopted by the general population. However, there is a tradeoff between compliance and power in these systems. We investigated the physiological benefits of using an inconspicuous, soft and passive assistive device which would avoid bulkiness, heaviness and user discomfort. We chose to assist the sit-to-stand (STS) maneuver because it is a common activity of daily living (ADL). STS is also recognized as one of the most challenging ADLs due to the high knee torque required, and the primary limiting factor is known to be knee extensor strength. Thus, the objective of this research was to develop and evaluate an unobtrusive knee assist wear called X-tights that could aid knee extension during STS using only soft and passive components. This was accomplished by routing elastic bands across the lower extremity. Thirty-one healthy participants performed STS tests with and without the X-tights, while metabolic cost and muscle activity were recorded. Metabolic power significantly decreased, by 3.2 ± 1.5% (P = 0.04), when utilizing the X-tights during the STS, while there was no statistically significant differences in muscle activity. The present work introduces a new soft and passive assist wear that can be worn inconspicuously under normal clothing, and we demonstrate promising results for the future development and integration of soft assistive technology for daily life.

Age-related differences in vastus lateralis fascicle behavior during fast accelerative leg-extension movements

Leg-extensor rate of power development (RPD) decreases during aging. This study aimed to identify the underlying mechanism of the age-related decline in RPD during a fast acceleration in terms of in vivo vastus lateralis (VL) fascicle shortening behavior. Thirty-nine men aged between 25 and 69 years performed three maximal isokinetic leg-extensor tests with a fixed initial acceleration of 45° knee extension in 150 ms until 340°/s knee angular velocity. RPD, VL activity, and ultrasound images were recorded to assess (relative) fascicle shortening and mean shortening velocity for the phases of electromechanical delay, pretension, and acceleration. Our findings show that fascicle shortening and mean shortening velocity during a fast action increase with aging (0.002 per year, P = .035 and 0.005 s^-1 per year, P = .097, respectively), mainly due to a higher amount of shortening in the phase of electromechanical delay. The ratio of VL fascicle length over upper leg length at rest showed a negative correlation (r = -.46, P = .004) with RPD/body mass, while pennation angle at rest showed a trend toward a positive correlation (r = .28, P = .089). To conclude, our findings indicate that the ability to reach high VL fascicle shortening velocities in vivo is not reduced in older men while performing preprogrammed fast accelerations. The greater amount of fascicle shortening in old age is probably the result of age-related differences in the tendinous properties of the muscle-tendon complex, forcing the fascicles to shorten more in order to transmit the muscle force to the segment.

Rehabilitative Impact of Exercise Training on Human Skeletal Muscle Transcriptional Programs in Parkinson's Disease

Parkinson's disease (PD) is the most common motor neurodegenerative disease, and neuromuscular function deficits associated with PD contribute to disability. Targeting these symptoms, our laboratory has previously evaluated 16-week high-intensity resistance exercise as rehabilitative training (RT) in individuals with PD. We reported significant improvements in muscle mass, neuromuscular function (strength, power, and motor unit activation), indices of neuromuscular junction integrity, total and motor scores on the unified Parkinson's disease rating scale (UPDRS), and total and sub-scores on the 39-item PD Quality of Life Questionnaire (PDQ-39), supporting the use of RT to reverse symptoms. Our objective was to identify transcriptional networks that may contribute to RT-induced neuromuscular remodeling in PD. We generated transcriptome-wide skeletal muscle RNA-sequencing in 5 participants with PD [4M/1F, 67 ± 2 years, Hoehn and Yahr stages 2 (n = 3) and 3 (n = 2)] before and after 16-week high intensity RT to identify transcriptional networks that may in part underpin RT-induced neuromuscular remodeling in PD. Following RT, 304 genes were significantly upregulated, notably related to remodeling and nervous system/muscle development. Additionally, 402 genes, primarily negative regulators of muscle adaptation, were downregulated. We applied the recently developed Pathway-Level Information ExtractoR (PLIER) method to reveal coordinated gene programs (as latent variables, LVs) that differed in skeletal muscle among young (YA) and old (OA) healthy adults and PD (n = 12 per cohort) at baseline and in PD pre- vs. post-RT. Notably, one LV associated with angiogenesis, axon guidance, and muscle remodeling was significantly lower in PD than YA at baseline and was significantly increased by exercise. A different LV annotated to denervation, autophagy, and apoptosis was increased in both PD and OA relative to YA and was also reduced by 16-week RT in PD. Thus, this analysis identified two novel skeletal muscle transcriptional programs that are dysregulated by PD and aging, respectively. Notably, RT has a normalizing effect on both programs in individuals with PD. These results identify potential molecular transducers of the RT-induced improvements in neuromuscular remodeling and motor function that may aid in optimizing exercise rehabilitation strategies for individuals with PD.

Comparisons of Knee Extensor Functional Demand During Gait by Age, Physical Activity Level, and the Impact of Acute Exercise and Walking Speed

The link between age-related changes in muscle strength and gait is unclear. We tested if knee extensor functional demand differs by age and physical activity status and if functional demand increases with walking speed or after exercise. Gait and knee extensor muscle torque were collected from young adults and highly and less active older adults before and after treadmill walking. Functional demand was the ratio of knee moments during gait to knee extensor muscle torques estimated from participant-specific torque-velocity curves. Functional demand at the peak knee flexion moment was greater in less active older adults than young adults (29.3% [14.3%] vs 24.6% [12.1%]) and increased with walking speed (32.0% [13.9%] vs 22.8% [10.4%]). Functional demand at both knee extension moments increased ∼2% to 3% after exercise. The low functional demand found in this study suggests that healthy adults maintain a reserve of knee extensor strength.

Metformin blunts muscle hypertrophy in response to progressive resistance exercise training in older adults: A randomized, double-blind, placebo-controlled, multicenter trial: The MASTERS trial

Progressive resistance exercise training (PRT) is the most effective known intervention for combating aging skeletal muscle atrophy. However, the hypertrophic response to PRT is variable, and this may be due to muscle inflammation susceptibility. Metformin reduces inflammation, so we hypothesized that metformin would augment the muscle response to PRT in healthy women and men aged 65 and older. In a randomized, double‐blind trial, participants received 1,700 mg/day metformin (N = 46) or placebo (N = 48) throughout the study, and all subjects performed 14 weeks of supervised PRT. Although responses to PRT varied, placebo gained more lean body mass (p = .003) and thigh muscle mass (p < .001) than metformin. CT scan showed that increases in thigh muscle area (p = .005) and density (p = .020) were greater in placebo versus metformin. There was a trend for blunted strength gains in metformin that did not reach statistical significance. Analyses of vastus lateralis muscle biopsies showed that metformin did not affect fiber hypertrophy, or increases in satellite cell or macrophage abundance with PRT. However, placebo had decreased type I fiber percentage while metformin did not (p = .007). Metformin led to an increase in AMPK signaling, and a trend for blunted increases in mTORC1 signaling in response to PRT. These results underscore the benefits of PRT in older adults, but metformin negatively impacts the hypertrophic response to resistance training in healthy older individuals. ClinicalTrials.gov Identifier: NCT02308228.

The Roles of Sex and Physical Activity in Gait and Knee Extensor Function With Age

Older females experience higher rates of disability than males, potentially due to sex-specific differences in gait and muscle function. The authors evaluated the effects of age and physical activity (PA) on gait mechanics and knee extensor muscle function in males and females. Three groups of 20 individuals (each 10 females) participated: young (21-35 y) and highly and less active older (55-70 y) adults. Knee extensor strength and joint mechanics during preferred speed gait were collected before and after 30 minutes of walking. Age by sex and PA by sex interactions indicated older and less active older females had lower concentric knee extensor muscle power and larger hip extension moments than males. After 30 minutes of walking, older less active adults had larger decreases in knee extensor power than their highly active older counterparts, and older adults of both sexes had decreases in ankle dorsiflexion moments while young adults did not. These results suggest that older, particularly less active, adults are susceptible to knee extensor muscle fatigue from moderate activity. For older adults, high levels of PA may be necessary to preserve gait mechanics in response to a bout of exercise. This new information may be important for targeting interventions in at-risk older adults.

The Automatic Assessment of Strength and Mobility in Older Adults: A Test-Retest Reliability Study

Background: Simple field tests such as the Timed Up and Go test (TUG) and 30 s Chair Stand test are commonly used to evaluate physical function in the elderly, providing crude outcome measures. Using an automatic chronometer, it is possible to obtain additional kinematic parameters that may lead to obtaining extra information and drawing further conclusions. However, there is a lack of studies that evaluate the test-retest reliability of these parameters, which may help to judge and interpret changes caused by an intervention or differences between populations. Thus, the aim of this study was to evaluate the test-retest reliability of the Timed Up and Go test (TUG) and 30 s Chair Stand test in healthy older adults. Methods: A total of 99 healthy older adults participated in this cross-sectional study. The TUG and the 30 s Chair Stand test were performed five times and twice, respectively, using an automatic chronometer. The sit-to-stand-to-sit cycle from the 30 s Chair Stand test was divided into two phases. Results: Overall, reliability for the 30 s Chair Stand test was good for almost each variable (intraclass correlation coefficient (ICC) >0.70). Furthermore, the use of an automatic chronometer improved the reliability for the TUG (ICC >0.86 for a manual chronometer and ICC >0.88 for an automatic chronometer). Conclusions: The TUG and the 30 s Chair Stand test are reliable in older adults. The use of an automatic chronometer in the TUG is strongly recommended as it increased the reliability of the test. This device enables researchers to obtain relevant and reliable data from the 30 s Chair Stand test, such as the duration of the sit-to-stand-to-sit cycles and phases.

The Importance of Resistance Exercise Training to Combat Neuromuscular Aging

Older adults undergoing age-related decrements in muscle health can benefit substantially from resistance exercise training, a potent stimulus for whole muscle and myofiber hypertrophy, neuromuscular performance gains, and improved functional mobility. With the use of advancing technologies, research continues to elucidate the mechanisms of and heterogeneity in adaptations to resistance exercise training beyond differences in exercise prescription. This review highlights the current knowledge in these areas and emphasizes knowledge gaps that require future attention of the field.

A body-fixed-sensor-based analysis of stair ascent and sit-to-stand to detect age-related differences in leg-extensor power

Human ageing is accompanied by a progressive decline in leg-extensor power (LEP). LEP is typically measured with specialized and expensive equipment, which limits the large-scale applicability. Previously, sensor-based trunk kinematics have been used to estimate the vertical power required to elevate the body’s center of mass during functional tests, but the link with LEP and age remains to be investigated. Therefore, we investigated whether a body-fixed sensor-based analysis of power during stair ascent (SA) and sit-to-stand (STS) is positively related to LEP and whether its ability to detect age-related declines is similar. In addition, the effect of load during SA and STS was investigated. 98 adults (20–70 years) performed a leg press to assess LEP, SA and 5-repetition STS tests. In SA and STS, two conditions were tested: unloaded and loaded (+10% body mass). An inertial measurement unit was used to analyze (sub)-durations and vertical power. SA and STS power were more related to LEP than duration parameters (i.e. 0.80–0.81 for power and -0.41 –-0.66 for duration parameters, p < 0.05). The average annual age-related percent change was higher in SA power (-1.38%) than in LEP (-0.86%) and STS power (-0.38%) (p < 0.05). Age explained 29% in SA power (p < 0.001), as opposed to 14% in LEP (p < 0.001) and a non-significant 2% in STS power (p = 0.102). The addition of 10% load did not influence the age-related decline of SA and STS power nor the relationship with LEP. These results demonstrate the potential of SA tests to detect age-related deterioration in neuromuscular function. SA seems more sensitive to detect age-related changes than LEP, probably because of the additional balance component and plantar- and dorsiflexor activity. On the contrary, STS is less sensitive to age-related changes because of a ceiling effect in well-functioning adults.

Age related changes of the motor excitabilities and central and peripheral muscle strength

INTRODUCTION

The purpose was to investigate the age effects on central versus peripheral sources of strength, fatigue, and central neural excitabilities.

METHODS

42 healthy subjects were recruited as young group (23.73 ± 2.15 years; n = 26) and middle-aged group (57.25 ± 4.57 years; n = 16). Maximum voluntary contraction force (MVC), voluntary activation level (VA), and twitch force of quadriceps were evaluated to represent general, central, and peripheral strengths. Central and peripheral fatigue indexes were evaluated using femoral nerve electrical stimulation. Cortical excitabilities were evaluated using transcranial magnetic stimulation (TMS).

RESULTS

The middle-aged group had lower MVC and twitch force of quadriceps, but not VA, than young group. No between group differences were found in fatigue indexes. The cortical excitability in middle-aged group was different from young group in paired TMS with inter-stimulus interval of 7 ms.

CONCLUSION

The age-related strength loss at early stage was primarily caused by peripheral muscular strength. The deviation of central neural excitability can be detected but the activation level was not impaired in middle-age adults.

A 'Movement Screening Test' of Functional Control Ability in Female Recreation Golfers and Non-Golfers over the Age of 80 Years: A Reliability Study

Assessing function in elderly populations predominantly aims to quantify the risk of falling. Current assessment methods do not consider changes associated with aging in movement coordination patterns and the ability to control movement. The aim of this study was to examine the intra-rater reliability of a 'Movement Screening Test' (MST) in females over 80 years across a range of physical activity levels, who were golfers and non-golfers. Female recreational golfers (N = 21) and non-golfers (N = 10) aged 80 to 87 years performed the MST. The MST consists of three tests: Test 1, sit to stand with arm lift; Test 2, trunk lean with knee bend and opposite arm lift; Test 3, chest rotation with neutral head and pelvis. Videos of the MST were analyzed and scored according to specific criteria. The videos were reviewed on two separate occasions to quantify the intra-rater reliability of scoring of the MST. Intra-rater reliability ( κ ) of the MST demonstrated substantial agreement for 11/23 criteria ( κ = 0.65 and to 0.78) and excellent agreement for 9/23 criteria ( κ = 0.81 to 1). Therefore, the reliability of the MST for women aged 80 years and over was established. The MST test and scoring system may be further refined to improve reliability. Further investigations could explore coordination patterns in older people, how these relate to various aspects of musculoskeletal function, and how they vary between different populations.

The influence of knee extensor fatigue on lower extremity muscle activity during chair rise in young and older adults

PURPOSE

The purpose of this investigation was to evaluate alterations in muscular effort and temporal characteristics of their activity during the sit-to-stand (STS) due to isolated fatiguing of the knee extensors, as indicated by declines in torque output.

METHODS

Surface electromyography of the lower extremity was recorded in healthy young (n = 11) and older (n = 11) adults as they ascended from a seated position, before and after dynamic knee extension exercise.

RESULTS

Knee extensor fatigue caused significant increases in soleus, gastrocnemius, and gluteus maximus relative effort (%MVC) in both age groups during the STS task. Rectus femoris %MVCs in both young and older adults significantly increased to similar extents throughout the STS movement, whereas vastus lateralis amplitudes only increased in preparation for seat-off. Muscle temporal characteristics appeared to generally be invariant with fatigue, except for earlier activation onset for the ankle musculature in older adult participants.

CONCLUSIONS

These findings demonstrate that isolated knee extension fatiguing exercise caused compensatory changes in muscle activation patterns and increased reliance of non-fatigued muscles at the ankle and hip as well as increased activity of synergist muscles during the STS. Moreover, this occurred to similar extents in older adults who had lower knee extensor strengths and greater quadriceps %MVCs in comparison to their younger counterparts, regardless of fatigue condition.

Effects of linear periodization versus daily undulating periodization on neuromuscular performance and activities of daily living in an elderly population

BACKGROUND

Periodization is a systematic training calendar designed to provide variations in performance targeting, while maximizing results and reducing the potential for overtraining. When provided across multiple weeks, termed a mesocycle, it may also incorporate active recovery periods using specified drills designed to translate neuromuscular gains into targeted functional abilities. There are a number of models that can be used when applying periodization to resistance training (RT). Among the most common are the linear (LP) and daily fixed non-linear (NLP) models. It is currently unknown whether an optimal periodization strategy exists that will maximize benefits for older adults; therefore, we compared the impact of these two periodization models on neuromuscular and functional measures in a group of older persons living independently in the community.

METHODS

Thirty-six older adults, 58-80 years of age, were randomly assigned to either a LP (n = 16; 69.3 ± 4.6 y) or NLP (n = 14; 68.9 ± 6.7 y) group. The LP group performed 12 weeks of training comprised of separate 4-week strength and power training cycles, each followed by a 2-week recovery period incorporating translational exercises. The NLP group performed the strength, power, and translational training on three separate days during the week. Neuromuscular testing included seated chest press and leg press strength and power tests, while physical function testing included the gallon jug shelf test, laundry transfer test, floor stand-up, chair-to-stand test, and 8 foot timed up-and-go.

RESULTS

3 (time) × 2 (sex) × 2 (group) repeated measures ANOVA revealed both periodization strategies were equally effective at inducing neuromuscular and functional improvements and that men generally produced more strength and power than women.

CONCLUSIONS

Both LP and NLP can be used to improve strength, power, and functional performance in healthy untrained older adults when strength, power and functional training cycles are involved. Therefore, personal preference and variety should be considered when deciding which approach to use, provided high-speed power and translational recovery components are included.

Age affects myosin relaxation states in skeletal muscle fibers of female but not male mice

The recent discovery that myosin has two distinct states in relaxed muscle–disordered relaxed (DRX) and super-relaxed (SRX)–provides another factor to consider in our fundamental understanding of the aging mechanism in skeletal muscle, since myosin is thought to be a potential contributor to dynapenia (age-associated loss of muscle strength independent of atrophy). The primary goal of this study was to determine the effects of age on DRX and SRX states and to examine their sex specificity. We have used quantitative fluorescence microscopy of the fluorescent nucleotide analog 2′/3′-O-(N-methylanthraniloyl) ATP (mantATP) to measure single-nucleotide turnover kinetics of myosin in skinned skeletal muscle fibers under relaxing conditions. We examined changes in DRX and SRX in response to the natural aging process by measuring the turnover of mantATP in skinned fibers isolated from psoas muscle of adult young (3–4 months old) and aged (26–28 months old) C57BL/6 female and male mice. Fluorescence decays were fitted to a multi-exponential decay function to determine both the time constants and mole fractions of fast and slow turnover populations, and significance was analyzed by a t-test. We found that in females, both the DRX and SRX lifetimes of myosin ATP turnover at steady state were shorter in aged muscle fibers compared to young muscle fibers (p ≤ 0.033). However, there was no significant difference in relaxation lifetime of either DRX (p = 0.202) or SRX (p = 0.804) between young and aged male mice. No significant effects were measured on the mole fractions (populations) of these states, as a function of sex or age (females, p = 0.100; males, p = 0.929). The effect of age on the order of myosin heads at rest and their ATPase function is sex specific, affecting only females. These findings provide new insight into the molecular factors and mechanisms that contribute to aging muscle dysfunction in a sex-specific manner.

A Comparison of Load-Velocity and Load-Power Relationships Between Well-Trained Young and Middle-Aged Males During Three Popular Resistance Exercises

Fernandes, JFT, Lamb, KL, and Twist, C. A comparison of load-velocity and load-power relationships between well-trained young and middle-aged males during 3 popular resistance exercises. J Strength Cond Res 32(5): 1440-1447, 2018-This study examined the load-velocity and load-power relationships among 20 young (age 21.0 ± 1.6 years) and 20 middle-aged (age 42.6 ± 6.7 years) resistance-trained males. Participants performed 3 repetitions of bench press, squat, and bent-over-row across a range of loads corresponding to 20-80% of 1 repetition maximum (1RM). Analysis revealed effects (p < 0.05) of group and load × group on barbell velocity for all 3 exercises, and interaction effects on power for squat and bent-over-row (p < 0.05). For bench press and bent-over-row, the young group produced higher barbell velocities, with the magnitude of the differences decreasing as load increased (ES; effect size 0.0-1.7 and 1.0-2.0, respectively). Squat velocity was higher in the young group than the middle-aged group (ES 1.0-1.7) across all loads, as was power for each exercise (ES 1.0-2.3). For all 3 exercises, both velocity and 1RM were correlated with optimal power in the middle-aged group (r = 0.613-0.825, p < 0.05), but only 1RM was correlated with optimal power (r = 0.708-0.867, p < 0.05) in the young group. These findings indicate that despite their resistance training, middle-aged males were unable to achieve velocities at low external loads and power outputs as high as the young males across a range of external resistances. Moreover, the strong correlations between 1RM and velocity with optimal power suggest that middle-aged males would benefit from training methods which maximize these adaptations.

Internal Loads, but Not External Loads and Fatigue, Are Similar in Young and Middle-Aged Resistance-Trained Males during High Volume Squatting Exercise †

Little is known about the internal and external loads experienced during resistance exercise, or the subsequent fatigue-related response, across different age groups. This study compared the internal (heart rate, OMNI ratings of perceived exertion (RPE), session RPE) and external loads (peak velocity and power and volume load) during high volume squatting exercise (10 × 10 at 60% one-repetition maximum (1RM)) and the fatigue-related response (maximal voluntary contraction (MVC), voluntary activation (VA), resting doublet force, peak power, and blood lactate) in young (n = 9; age 22.3 ± 1.7 years) and middle-aged (n = 9; age 39.9 ± 6.2 years) resistance-trained males. All internal load variables and peak velocity illustrated unclear differences between groups during exercise. Peak power and volume load were likely higher in the young group compared to their middle-aged counterparts. The unclear differences in MVC, VA and blood lactate between groups after exercise were accompanied by very likely greater decrements in resting doublet force and peak power at 20 and 80% 1RM in the middle-aged group compared to the young group. These data indicate that internal load is not different between young and middle-aged resistance-trained males, though certain external load measures and the fatigue response are.

Skeletal Muscle Function in the Oldest-Old: The Role of Intrinsic and Extrinsic Factors

Although skeletal muscle function is diminished with advanced age, single muscle fiber function seems to be preserved. Therefore, this review examines the hypothesis that the skeletal muscle fiber, per se, is not the predominant factor responsible for the reduction in force-generating capacity in the oldest-old, but, rather, is attributable to a combination of factors external to the muscle fibers.

Age related differences in segment coordination and its variability during gait

BACKGROUND

Aging is associated with a loss of mobility and altered gait mechanics. Loss of function and mobility may be due to or exacerbated by low levels of physical activity in the aged. The mechanisms linking age-related changes in physiology, altered mobility and gait may be elucidated by examining movement coordination and coordination variability.

RESEARCH QUESTION

The purpose of this study was to examine the impacts of age and habitual physical activity level on segment coordination and coordination variability during gait.

METHODS

A modified vector coding technique was used to calculate segment coordination and coordination variability during treadmill gait for three groups of healthy adults: young (21-35 years), older highly active (55-70 years), and older less active (55-70 years). Segment couples of interest included those whose coordination could contribute to typical age-related changes in gait mechanics at the hip, knee, and ankle.

RESULTS

Differences in coordination and its variability occurred mainly during terminal swing and midstance and in couples across the hip and ankle. Across the hip, coordination differed between older highly active adults and the other cohorts, while variability was higher in young compared to all older adults. Across the ankle, young adults displayed different coordination and greater variability than all older adults except for the sagittal couple in midstance, where older highly active adults had greater coordination variability than the other cohorts.

SIGNIFICANCE

These results suggest that older adults, independent of habitual physical activity, may use a different strategy to control hip and ankle motion during periods of single-limb stance.