Acute Effect of Dynamic and Gluteal Resistance Exercise Warm-up Protocols on Jump Landing Mechanics in College-Aged Females.

ABSTRACT: Rauseo, ML, Feairheller, DL, LaRoche, DP, and Cook, SB. Acute effect of dynamic and gluteal resistance exercise warm-up protocols on lower-extremity jump landing mechanics in college-aged females. J Strength Cond Res 38(2): 259-265, 2024-Inadequate neuromuscular control of the femur by the gluteal musculature is associated with noncontact and overuse injuries to the knee. Acute bouts of resistance exercises targeting the gluteal musculature can be prescribed as part of a warm-up protocol with the goal of improving subsequent neuromuscular control and performance. The purpose of this study was to determine the effect that a warm-up protocol including moderate-intensity gluteal resistance exercises (GRE) has on single leg jump landing biomechanics. Seventeen healthy, college-aged, recreationally active females (mean ± SD ; age = 21.4 ± 1.9 years; height = 166.9 ± 5.7 cm; body mass = 62.5 ± 7.4 kg) performed 3 single leg hop trials per leg after completing no warm-up (CON), a dynamic warm-up (DWU), and a dynamic warm-up with gluteal resistance exercises (DWU + GRE) across 3 laboratory visits. Lower extremity kinetic and kinematic variables were assessed during single leg hops from the point of initial foot contact to deepest knee flexion. Biomechanical differences between dominant and nondominant limb landings were also assessed. Dominant limb hip internal rotation angle after DWU + GRE (2.03 ± 9.92°) was significantly greater ( p ≤ 0.05) compared with CON (-3.36 ± 7.74°). Peak knee adduction moment (56.8%), peak knee flexion angle (5.7%), and peak knee external rotation angle (17.0%) were significantly greater ( p ≤ 0.017) in the dominant limb, compared with the nondominant limb, across warm-up protocols. The combined DWU + GRE warm-up protocol did not have a substantial impact on landing biomechanics. Clinicians prescribing GRE before activity should not expect significant changes in movement patterns after a single bout.

Validation of Smartphone Accelerometry for the Evaluation of Sit-To-Stand Performance and Lower-Extremity Function in Older Adults.

This study tested the concurrent and construct validity of smartphone accelerometry measurement of sit-to-stand (STS) performance in individuals aged 65-89 years. Normal and fast STS times were recorded by smartphone accelerometer, force plate, and video motion systems concurrently, and isokinetic knee extension power and STS whole-body power were obtained. Normal and fast speed STS times from a smartphone accelerometer agreed closely with force plate and motion system methods (mean difference = 0.04 s). Normal and fast STS times were inversely related to isokinetic knee extension power (r = -.93, p < .001 and r = -.82, p < .001, respectively) and STS whole-body power (r = -.76, p < .001 and r = -.70, p < .001, respectively). The STS time obtained from a smartphone accelerometer was equivalent to the established, precise measures of STS time and was related to lower-extremity power, making it a potentially useful metric of lower-extremity function.

Acute Effects of Static and Ballistic Stretching on Muscle-Tendon Unit Stiffness, Work Absorption, Strength, Power, and Vertical Jump Performance.

ABSTRACT: Gesel, FJ, Morenz, EK, Cleary, CJ, and LaRoche, DP. Acute effects of static and ballistic stretching on muscle-tendon unit stiffness, work absorption, strength, power, and vertical jump performance. J Strength Cond Res 36(8): 2147-2155, 2022-The purpose of this study was to evaluate the effects of static and ballistic stretching on muscle-tendon unit (MTU) stiffness, work absorption (WA), strength, power, and countermovement vertical jump (CMJ) performance. Using a within-subject design, 22 subjects performed 3 separate experimental conditions: no-stretching, ballistic stretching, and static stretching for the quadriceps, hamstrings, gluteus, and plantarflexor muscle groups. After each condition, plantarflexor MTU stiffness, WA, isometric strength, and power were measured, followed by a CMJ on a force plate to obtain peak center of mass velocity, peak power, rate of force development, peak force, work, and vertical jump height. Repeated measures analysis of variance with Bonferroni corrected post-hoc tests were used to detect differences between conditions for plantarflexor and CMJ measures. An acute bout of static stretching significantly reduced WA by 12% ( p = 0.049) and isokinetic power by 8% ( p = 0.047) compared with the control condition but ballistic stretching did not ( p = 0.624, p = 0.692, respectively). Significant positive correlations existed between MTU stiffness, WA, strength, and power ( r = 0.64-0.77, p < 0.001). Despite significant positive correlations between MTU stiffness, WA, and CMJ performance measures ( r = 0.40-0.72, p < 0.001), neither static nor ballistic stretching affected CMJ performance ( p > 0.05). These data show that stiffer MTU that absorb more work (energy) are associated with greater muscle force, power, and CMJ performance. Although an acute bout of static stretching impaired MTU passive-elastic properties and power production, neither static nor ballistic stretching impaired isometric strength or CMJ performance.

Asymmetry of lower extremity force and muscle activation during knee extension and functional tasks.

INTRODUCTION: Strength and power asymmetries of >10% may negatively impact physical function. METHODS: Twenty-four healthy participants, 30-60 years of age, were assessed for muscle power asymmetry during isokinetic knee extension and ground reaction force asymmetry during chair-rise and vertical jump tasks. Neuromuscular activation asymmetry and coactivation of vastus lateralis (VL) and biceps femoris (BF) were assessed in each condition. Symmetric (SG) and asymmetric (AG) groups were identified using a 10% knee extension power asymmetry criterion. RESULTS: The AG had greater chair-rise rate of force development asymmetry (P = 0.003, d = 1.29), but a similar chair-rise and vertical jump peak force asymmetry as the SG. Large group effects were found for VL activation asymmetry during knee extension (P = 0.047, d = 0.87), BF activation asymmetry during vertical jump (P = 0.015, d = 1.12), and strong leg coactivation during vertical jump (P = 0.028, d = 0.96). CONCLUSIONS: Compensation for muscle power asymmetry may occur during functional tasks, potentially through differential activation of strong and weak leg muscles. Muscle Nerve 56: 495-504, 2017.

Utility of electromyographic fatigue threshold during treadmill running.

INTRODUCTION: We investigated 2 different methods for determining muscle fatigue threshold by electromyography (EMG). METHODS: Thirteen subjects completed an incremental treadmill running protocol for EMG fatigue threshold (EMGFT ) determination based on the critical power concept (EMGFT 1) and the breakpoint in the linear relationship between EMG amplitude and exercise intensity (EMGFT 2). Then, both the EMGFT 1 and EMGFT 2 were tested in a continuous treadmill running protocol. EMG was recorded from the rectus femoris (RF), vastus lateralis (VL), biceps femoris (BF), and lateral gastrocnemius (LG) muscles. RESULTS: For BF, EMGFT 2 was higher than EMGFT 1, and EMGFT 1 for BF was lower than EMGFT 1 for LG. EMG of RF was higher at EMGFT 2 than at EMGFT 1, and LG EMG was lower at EMGFT 2. CONCLUSIONS: EMGFT can be determined during a single treadmill running test, and EMGFT 1 may be the most appropriate method to estimate the muscle fatigue threshold during running.

Effect of cryotherapy on muscle recovery and inflammation following a bout of damaging exercise.

The purpose of this study was to determine the effect of cryotherapy on the inflammatory response to muscle-damaging exercise using a randomized trial. Twenty recreationally active males completed a 40-min run at a -10 % grade to induce muscle damage. Ten of the subjects were immersed in a 5 °C ice bath for 20 min and the other ten served as controls. Knee extensor peak torque, soreness rating, and thigh circumference were obtained pre- and post-run, and 1, 6, 24, 48, and 72 h post-run. Blood samples were obtained pre- and post-run, and 1, 6 and 24 h post-run for assay of plasma chemokine ligand 2 (CCL2). Peak torque decreased from 270 ± 57 Nm at baseline to 253 ± 65 Nm post-run and increased to 295 ± 68 Nm by 72 h post-run with no differences between groups (p = 0.491). Soreness rating increased from 3.6 ± 6.0 mm out of 100 mm at baseline to 47.4 ± 28.2 mm post-run and remained elevated at all time points with no differences between groups (p = 0.696). CCL2 concentrations increased from 116 ± 31 pg mL(-1) at baseline to 293 ± 109 pg mL(-1) at 6 h post-run (control) and from 100 ± 27 pg mL(-1) at baseline to 208 ± 71 pg mL(-1) at 6 h post-run (cryotherapy). The difference between groups was not significant (p = 0.116), but there was a trend for lower CCL2 in the cryotherapy group at 6 h (p = 0.102), though this measure was highly variable. In conclusion, 20 min of cryotherapy was ineffective in attenuating the strength decrement and soreness seen after muscle-damaging exercise, but may have mitigated the rise in plasma CCL2 concentration. These results do not support the use of cryotherapy during recovery.

Comparison of the H:Q Ratio Between the Dominant and Nondominant Legs of Soccer Players: A Meta-analysis.

CONTEXT: Soccer players often have a dominant (D) leg, which could influence the relative strength between the quadriceps and hamstrings. The hamstring-to-quadriceps (H:Q) ratio can be assessed on a dynamometer at various velocities to provide information on injury risk. OBJECTIVE: To assess the concentric hamstrings and concentric quadriceps strength ratio (conventional H:Q ratio) assessed in D and nondominant (ND) legs at various speeds in male soccer players. DATA SOURCES: A systematic literature search was completed from inception to 2020 in PubMed, Academic Search Ultimate, CINAHL, and SPORTDiscus. STUDY SELECTION: Keywords associated with the H:Q ratio were connected with terms for soccer players. Titles and abstracts were screened by 2 reviewers based on inclusion and exclusion criteria related to sex, playing level, language, and measurement. A total of 81 studies were reviewed and 17 studies (21%) were used. STUDY DESIGN: A meta-analysis with random effects modeling generated standardized mean differences with 95% CIs between legs and speeds. LEVEL OF EVIDENCE: Level 3. DATA EXTRACTION: A total of 38 cohorts were identified, with 14, 13, and 11 cohorts assessed at low, intermediate, and high velocities, respectively. The Quality Assessment Tool for Observational Cohort and Cross-sectional Studies from the National Institutes of Health was used. RESULTS: The mean H:Q ratio at low velocities was 59.8 ± 9.5% in D leg and 58.6 ± 9.9% in ND leg, 64.2 ± 10.7% (D) and 63.6 ± 11.3% (ND) at the intermediate velocity, and 71.9 ± 12.7% (D) and 72.8 ± 12.7% (ND) at the high velocity. Low, intermediate, and high velocities had small effects of 0.13, 0.10, and -0.06, respectively. CONCLUSION: Conventional H:Q ratios vary across velocities but did not differ between D and ND limbs in male soccer players. This study may provide the foundation to establish norms and clinically meaningful differences.

Grade influences blood lactate kinetics during cross-country skiing.

The purpose of this study was to examine the effects of level vs. graded skate skiing on capillary blood lactate (B(La)), heart rate (HR), oxygen consumption (V(O2)), and training intensity prescriptions. Eleven Nordic skiers completed 2 submaximal skate roller skiing treadmill protocols during which intensity was increased either by grade (G(inc)) or by speed (S(inc)). The protocols were compared for prethreshold BLa, HR, and V(O2) at lactate threshold (LT) and the HR/V(O2) relationship. Additionally, double-pole (primarily upper body) and skating (arms and legs combined) protocols were used to measure peak V(O2) and peak HR. Heart rate and V(O2) at LT were lower during G(inc) compared with S(inc) (154.9 +/- 6.8 b.min(-1) vs. 162.0 +/- 9.1 b.min(-1) and 46.3 +/- 2.8 ml.kg(-1).min(-1) vs. 49.1 +/- 1.6 ml.kg(-1).min(-1), respectively, both p < 0.01). Pre-threshold B(La) and the HR/V(O2) relationship were not different between the submaximal protocols. V(O2) and HRpeak were higher in skating compared with double poling (64.6 +/- 1.8 ml.kg(-1).min(-1) vs. 60.3 +/- 2.8 ml.kg(-1).min(-1), 192.6 +/- 5.8 b.min(-1) vs. 187.8 +/- 6.7 b.min(-1), respectively, both p < 0.01). Greater reliance on upper-body musculature during graded skiing and its associated lower aerobic capacity increases B(La) when compared with level skiing. The leftward shift in the B(La) vs. intensity curve during uphill skiing should be recognized to properly prescribe training intensity as well as interpret laboratory results.

Caregiver perspectives on a smart home-based socially assistive robot for individuals with Alzheimer's disease and related dementia.

Purpose: Innovative assistive technology can address aging-in-place and caregiving needs of individuals with Alzheimer's disease and related dementia (ADRD). The purpose of this study was to beta-test a novel socially assistive robot (SAR) with a cohort of ADRD caregivers and gather their perspectives on its potential integration in the home context.Methods: The SAR involved a programmable research robot linked with commercially available Internet of things sensors to receive and respond to care recipient's behaviour. Eight caregivers observed the SAR perform two care protocols concerning the care recipient's daily routine and home safety, and then participated in a focus group and phone interview. The researchers used grounded theory and the Unified Theory of Acceptance and Use of Technology as a framework to gather and analyse the data.Results: The caregivers' asserted the potential of the SAR to relieve care burden and envisioned it as a next-generation technology for caregivers. Adoption of the SAR, as an identified theme, was subject to the SAR's navigability, care recipient engagement, adaptability, humanoid features, and interface design. In contrast, barriers leading to potential rejection were technological complexity, system failure, exasperation of burden, and failure to address digital divide.Conclusion: From a broader outlook, success of SARs as a home-health technology for ADRD is reliant on the timing of their integration, commercial viability, funding provisions, and their bonding with the care recipient. Long-term research in the home settings is required to verify the usability and impact of SARs in mediating aging-in-place of individuals with ADRD.IMPLICATIONS FOR REHABILITATIONSocially assistive robots (SARs), an emerging domain of assistive technology, are projected to have a crucial role in supporting aging-in-place of individuals with Alzheimer's disease and related dementia (ADRD).Caregivers of individuals with ADRD who observed and interacted with a novel SAR asserted their acceptance of the technology as well as its scope and feasibility for the upcoming generation of caregivers.Navigability, care recipient engagement, adaptability, humanoid features, and interface design were stated to be critical factors for SAR's acceptance by caregiver and care recipient dyads.In contrast, technological complexity, system failure, exasperation of burden, and failure to address digital divide are detrimental to SAR's adoption.Several design and implementation requirements must be considered towards the full-scale development and deployment of the SARs in the home context.

Influence of excess weight on lower-extremity vertical stiffness and metabolic cost of walking.

The purpose was to test whether lower-extremity vertical stiffness and gait mechanics explain differences in energy cost of walking (Cw) between individuals with normal weight (NW) and obesity (OB). Ten OB (33.1 ± 2.0 kg m-2) and 10 NW (24.2 ± 1.3 kg m-2) walked for six minutes on an instrumented treadmill at 1.25 m s-1 while Cw, lower-extremity kinematics, and vertical stiffness (K vert) were measured. NW completed another trial with a loaded vest (NWL) to simulate the BMI of the obese group. Cw was 24% greater in OB (277.5 ± 45.3 J m-1) and 23% greater in NWL (272.7 ± 35.7 J m-1) than NW (211.0 ± 27.0 J m-1, P < 0.005). Mass-specific Cw (Cwkg) wasn't different between conditions (P = 0.085). Lower-extremity K vert was 40% higher in OB (32.7 ± 5.2 kN m-1) than NW (23.3 ± 4.7 kN m-1, P < 0.001), but neither was different from NWL (27.5 ± 3.4 kN m-1, P > 0.05). Mass-specific K vert (P = 0.081) was similar across conditions. K vert was related to Cw (r = 0.55, P = 0.001). Cwkg wasn't different between NW or OB, but there was a negative correlation between BMI and Cwkg driven by lower Cwkg in NWL. Cw and K vert covaried in proportion to body mass, but mass-specific K vert was unrelated to Cwkg. Mass-specific K vert was lower in NWL than OB due to NWL's greater angle of attack, center of mass displacement, and joint range of motion.

Handgrip Strength Asymmetry and Weakness May Accelerate Time to Mortality in Aging Americans.

OBJECTIVES: Assessing handgrip strength (HGS) asymmetry may provide insights into HGS as a prognostic assessment of strength capacity and vitality. This study sought to determine the associations of HGS asymmetry and weakness on time to mortality in aging Americans. DESIGN: Longitudinal panel. SETTING: Secondary analyses of data from participants aged ≥50 years from the 2006‒2014 waves of the Health and Retirement Study. PARTICIPANTS: The analytic sample included 19,325 Americans who identified hand dominance and had measures of HGS for both hands in a single wave. MEASURES: A handgrip dynamometer was used to measure HGS. Men and women who were considered weak had HGS <26 kg and <16 kg, respectively. The highest HGS values from the dominant and nondominant hands were used to calculate HGS ratio: (nondominant HGS/dominant HGS). Those with HGS ratio <0.90 or >1.10 had any HGS asymmetry. Moreover, participants with HGS ratio <0.90 had dominant HGS asymmetry, whereas those with HGS ratio >1.10 had nondominant HGS asymmetry. The National Death Index and postmortem interviews verified date of death. Covariate-adjusted Cox models were used for analyses. RESULTS: Those with any HGS asymmetry had a 1.10 [95% confidence interval (CI) 1.03‒1.17] higher hazard for mortality, while those with weakness had a 1.44 (CI 1.32‒1.58) higher hazard for mortality. Likewise, participants with dominant HGS asymmetry had a 1.11 (CI 1.03‒1.18) higher hazard for mortality, and those with weakness had a 1.45 (CI 1.32‒1.58) higher hazard for mortality; however, the association was not significant for those with nondominant HGS asymmetry (hazard ratio: 1.07; CI 0.96‒1.18). CONCLUSIONS AND IMPLICATIONS: HGS asymmetry and weakness are markers of impaired strength capacity that independently accelerate time to mortality, but the magnitude of these associations was more prominent for weakness. Nevertheless, assessments of asymmetric HGS are a simple adjunct analysis that may show promise for increasing the prognostic value of handgrip dynamometers.

Initial neuromuscular performance in older women influences response to explosive resistance training.

The purpose of the study was to identify both demographic and neuromuscular traits that characterize successful or unsuccessful adaptation to resistance training in older women. Twelve, older women underwent electrically evoked muscle twitches for the knee extensors; and performed maximal, voluntary, isometric knee extensions, followed by eight weeks of resistance training. Prior to training nonresponders had 67% higher twitch peak torque than responders (0.29 ± 0.05 vs. 0.18 ± 0.06 Nm·kg(-1) respectively), 64% higher twitch rate of torque development (RTD) (3.96 ± 0.47 vs. 2.42 ± 0.62 Nm·s(-1)·kg(-1)), 51% higher voluntary peak torque (1.86 ± 0.40 vs. 1.23 ± 0.33 Nm·kg(-1)), 101% greater RTD (9.43 ± 1.52 vs. 4.70 ± 2.40 Nm·s(-1)·kg(-1)), 86% greater impulse (0.13 ± 0.01 vs. 0.07 ± 0.03 Nm·s·kg(-1)) and 27% faster motor time (80 ± 13 vs. 109 ± 34 ms), (all P < 0.05). Following training, responders showed an 11% increase in twitch peak torque over baseline (0.18 ± 0.06 to 0.20 ± 0.05 Nm·kg(-1)), 15% increase in voluntary peak torque (1.23 ± 0.33 to 1.41 ± 0.36 Nm·kg(-1)), 47% increase in RTD (4.70 ± 2.40 to 6.93 ± 2.02 Nm·s(-1)·kg(-1)), 43% increase in impulse (0.07 ± 0.03 to 0.10 ± 0.04 Nm·s·kg(-1)), and 26% increase in rate of EMG rise (886 ± 214 to 1116 ± 102 % pEMG·s(-1)) (all P < 0.05). Initially higher muscle mass and contractility, coupled with greater neural drive, likely explains why older women with good muscle performance seem to have a lower capacity for improvement than women with low initial levels of performance.

Hip extension power and abduction power asymmetry as independent predictors of walking speed in individuals with unilateral lower-limb amputation.

BACKGROUND: Preferred walking speed (PWS) is an indicator of walking ability, prosthetic walking potential, and function following a lower-limb amputation (LLA). There is a link between lower-limb muscle performance and PWS in individuals with LLA. However, the ability of select hip muscle performance parameters to determine PWS in these individuals still needs to be thoroughly investigated. RESEARCH QUESTION: Which hip muscle and joint torque parameters best determine PWS in persons with LLA? METHODS: Seventeen patients with LLA (6 transfemoral, 4 knee disarticulation, and 7 transtibial; 16 men, 1 woman; mean age ± standard deviation, 56 ± 15yr) participated in this cross-sectional study. Maximal joint torque and power were evaluated unilaterally, for both amputated and intact limbs, in isometric and isokinetic conditions during hip flexion/extension (60°/s and 180°/s) and abduction/adduction (30°/s and 90°/s). PWS was measured at habitual walking speed over a 10-m distance. Pearson's correlation coefficient was used to verify the degree of association between each torque parameter and PWS and multiple regression analysis was performed to identify the best predictors of PWS. The level of significance was p < 0.05. RESULTS: Correlations between hip muscle performance parameters and PWS were found in most cases (r = 0.51-0.82; p ≤ 0.036-0.0005). The multiple regression model revealed that the best independent predictors of PWS were hip extension power at 180°/s on the amputated side (r² = 0.672; p < 0.0005) and the asymmetry of hip abduction power at 30°/s (r² = -0.147; p < 0.008), accounting together for 82% of the variance in PWS. SIGNIFICANCE: Lesser hip extension power on the amputated side and greater hip abduction power asymmetry between limbs are detrimental to PWS in persons with LLA. These muscle groups and performance parameters should be considered during gait rehabilitation to assist individuals with LLA in achieving functional waking speed.

Chronic stretching and voluntary muscle force.

The purpose of the study was to determine whether muscle force, power, and optimal length were affected by 4 weeks of static or ballistic stretching. Twenty-nine males (age, 18-60 years) performed 4 maximal hip extensions to measure peak torque (PT), rate of torque development (RTD), work (W), and PT angle (PTA). Then, participants completed 4 weeks of static or ballistic flexibility training of the hip extensors followed by repetition of the testing protocol. After training, PT increased 5.3 +/- 19.0% in the static group (SG), 7.8 +/- 12.7% in the ballistic group (BG), and 6.1 +/- 17.9% in the control group (CG). RTD increased 4.8 +/- 22.7% in the SG, 3.6 +/- 28.0% in the BG and 9.7 +/- 24.0% in the CG. W increased 3.9 +/- 7.0% in the SG, 14.7 +/- 27.4% in the BG, and 5.5 +/- 9.5% in the CG. PTA changed little with a -1.6 +/- 6.6% decrease in the SG and increases of 0.86 +/- 4.1% in the BG and 0.18 +/- 8.7% in the CG. None of the results were statistically different between stretching group and CG (alpha = 0.05). These data suggest that 4 weeks of stretching have little effect on muscle strength, power, W, or length-tension relationship. PTA changed little, suggesting that a lengthening of the muscle with stretching did not occur. It is suggested that individuals can routinely stretch following exercise to maintain flexibility but should avoid stretching prior to exercise requiring high levels of muscle force. Before exercise that requires high muscular forces, individuals may perform dynamic, sport-specific exercises to increase blood flow, metabolic activity, temperature, and compliance of the muscle.

Physiological determinants of walking effort in older adults: should they be targets for physical activity intervention?

Older adults do not get enough physical activity increasing risk for chronic disease and loss of physical function. The purpose of this study was to determine whether neuromuscular, metabolic, and cardiorespiratory indicators of walking effort explain daily activity in community-dwelling older adults. Sixteen women and fourteen men, 78 ± 8 years, performed a steady-state walk on a treadmill at 1.25 m s-1 while muscle activation, heart rate, lactate, respiratory exchange ratio, oxygen consumption (VO2), ventilation, and rating of perceived exertion (RPE) were recorded as markers of Walking Effort. Daily walking time, sitting/lying time, energy expenditure, and up-down transitions were recorded by accelerometers as markers of Daily Activity. Structural equation modeling was used to explore the relationship between the latent variables Walking Effort and Daily Activity controlling for age and BMI. Participants spent 9.4 ± 1.9 h of the waking day sedentary and 1.9 ± 0.6 h walking. In the structural equation model, the latent variable Walking Effort explained 64% of the variance in the Daily Activity latent variable (ß = 0.80, p = 0.004). Walking Effort was identified by heart rate (ß = 0.64), ventilation (ß = 0.88), vastus lateralis activation (ß = 0.49), and lactate (ß = 0.58), all p < 0.05, but not RPE or VO2. Daily Activity was identified by stepping time (ß = 0.75) and up-down transitions (ß = 0.52), all p < 0.05. Walking effort mediated the effects of age and BMI on older adults' daily activity making physiological determinants of walking effort potential points of intervention.

Explosive force and fractionated reaction time in elderly low- and high-active women.

PURPOSE: The purpose of this study was to determine whether muscle power, activation time, and neuromuscular stimulation are related to physical activity patterns in older women. METHODS: Forty women (65-84 yr) were assigned to high-active (HA) and low-active (LA) groups on the basis of a historical activity questionnaire, and then they performed a series of maximal, voluntary, isometric knee extensions in a visually cued RT task. Fractionated RT measures were taken using three landmarks in the data: the presentation of the visual stimulus, the beginning of the EMG burst, and the initiation of force development. The rate and magnitude of neural stimulation were taken from surface EMG. RESULTS: Peak torque was 15% greater, rate of torque development was 26% greater, motor time was 17% shorter, rate of EMG rise was 25% faster, and onset EMG magnitude was 15% greater in HA than in LA subjects (P<0.05). CONCLUSION: These results indicate that older women with a history of vigorous activity can generate greater force, power, and motor output in comparison with their less active peers. The lower-body mass index of the HA subjects and 310% greater volume of physical activity are likely to account for the enhanced neuromuscular function seen. It is plausible that in addition to aging, physical inactivity is responsible for a large portion of the loss of neuromuscular function seen in older adults.

Plantarflexor passive-elastic properties related to BMI and walking performance in older women.

The objective of this study was to examine the influence of BMI on the passive-elastic properties of the ankle plantarflexors in older women. Twenty-three women, 65-80 yr, were separated into normal weight (NW, BMI <25.0kgm-2, n=11) and overweight-obese (OW, BMI≥25.0kgm-2, n=12) groups. Resistive torque of the ankle plantarflexors was recorded on an isokinetic dynamometer by passively moving the ankle into dorsiflexion. Stiffness, work absorption, and hysteresis were calculated across an ankle dorsiflexion angle of 10-15°. Maximal plantarflexor strength was assessed, then participants walked at maximal speed on an instrumented gait analysis treadmill while muscle activation (EMG) was recorded. Plantarflexor stiffness was 34% lower in OW (26.4±12.7Nmrad-1) than NW (40.0±15.7Nmrad-1, p=0.032). Neither work absorption nor hysteresis were different between OW and NW. Stiffness per kg was positively correlated to strength (r=0.66, p<0.001), peak vertical ground reaction force during walking (r=0.72, p<0.001), weight acceptance rate of force (r=0.51, p=0.007), push-off rate of force (r=0.41, p=0.026), maximal speed (r=0.61, p=0.001), and inversely correlated to BMI (r=-0.61, p=0.001), and peak plantarflexor EMG (r=-0.40, p=0.046). Older women who are OW have low plantarflexor stiffness, which may limit propulsive forces during walking and necessitate greater muscle activation for active force generation.

Knee extensor power asymmetry is unrelated to functional mobility of older adults.

PURPOSE: To determine whether knee extensor power asymmetry limits functional mobility of older adults who possess muscle weakness. METHODS: Knee extensor power was measured in 36 older men and women (76.0±7.6yr), for each leg, on an isokinetic dynamometer at 60, 180, and 300degs-1 and power asymmetry was calculated as the percent difference in power between strong and weak legs, at each isokinetic velocity. 400-m walk, stair ascent, and five-repetition chair rise tests were performed to assess functional mobility. Pearson correlations were used to examine the relationship between weak leg power, strong leg power, power asymmetry, and 400-m walk time, stair ascent time, and chair rise time. Participants were then stratified into low power-high asymmetry (LP-HA), low power-low asymmetry (LP-LA), high power-high asymmetry (HP-HA), and high power-low asymmetry (HP-LA) groups who were compared for functional mobility. RESULTS: Knee extensor power asymmetry was unrelated to 400-m walk time (r=0.16, p=0.180), stair ascent time (r=0.22, p=0.094), or chair rise time (r=0.03, p=0.437), whereas weak and strong leg powers were equally associated with 400-m time (r=-0.62, p<0.001; r=-0.62, p<0.001), stair ascent time (r=-0.55, p<0.001; r=-0.57, p<0.001), and chair rise time (r=-0.28, p=0.048; r=-0.31, p=0.032), respectively. Power asymmetry was lowest at 60degs-1 (12%), and increased with contraction velocity (p=0.001) to 15% at 180degs-1 and to 20% at 300degs-1. LP-HA exhibited 26% slower 400-walk time than HP-LA (p=0.015) and 19% slower than HP-HA (p=0.037). LP-HA had 31% slower stair ascent time than HP-LA (p=0.033). There were no differences in chair rise performance between groups. CONCLUSIONS: Knee extensor power asymmetry was unrelated to 400-m walk, stair ascent, and chair rise performance in older adults. Weak and strong limb powers were equally related to these functional measures, but a leftward shift of the power-mobility curve exists for the weak leg that may hinder clinical assessment if strength or power is measured on a single limb and symmetry is assumed. The greatest degree of knee extensor power asymmetry occurred at the fastest isokinetic velocity, which suggests high-speed muscle contractions may better differentiate laterality of function in older individuals.

Blood flow restricted resistance training in older adults at risk of mobility limitations.

High-load resistance training (HL) may be contraindicated in older adults due to pre-existing health conditions (e.g. osteoarthritis). Low-load blood flow restricted (BFR) resistance training offers an alternative to HL with potentially similar strength improvement. PURPOSE: To compare muscle strength, cross-sectional area (CSA), physical function, and quality of life (QOL) following 12-weeks of HL or BFR training in older adults at risk of mobility limitations. METHODS: Thirty-six males and females (mean: 75.6years 95% confidence interval: [73.4-78.5], 1.67m [1.64-1.70], 74.3kg [69.8-78.8]) were randomly assigned to HL (70% of one repetition maximum [1-RM]) or low-load BFR (30% 1-RM coupled with a vascular restriction) exercise for the knee extensors and flexors twice per week for 12weeks. A control (CON) group performed light upper body resistance and flexibility training. Muscle strength, CSA of the quadriceps, 400-m walking speed, Short Physical Performance Battery (SPPB), and QOL were assessed before, midway and after training. RESULTS: Within 6-weeks of HL training, increases in all strength measures and CSA were evident and the gains were significantly greater than the CON group (P<0.05). The BFR group had strength increases in leg extension and leg press 1-RM tests, but were significantly lower in leg extension isometric maximum voluntary contraction (MVC) and leg extension 1-RM than the HL group (P<0.01). At 12-weeks HL and BFR training did not differ in MVC (P=0.14). Walking speed increased 4% among all training groups (P<0.01) and no changes were observed for overall SPPB score and QOL (P>0.05). CONCLUSION: Both training programs resulted in muscle CSA improvements and HL training had more pronounced strength gains than BFR training after 6-weeks and were more similar to BFR after 12-weeks of training. These changes in both groups did not transfer to improvements in QOL, SPPB, and walking speed. Since both programs result in strength and CSA gains, albeit at different rates, future research should consider using a combination of HL and BFR training in older adults with profound muscle weakness and mobility limitations.