A Comprehensive Examination of Age-Related Lower Limb Muscle Function Asymmetries across a Variety of Muscle Action Types.

Previous research has found that lower limb muscle asymmetries increase with age and are linked to fall and injury risks. However, past studies lack a wide variety of muscle function modes and measures as well as comparison to a comparable younger age group. The purpose of this study was to examine age-related lower limb muscle function asymmetries across a variety of muscle action types and velocities in young and old adults. Lower limb balance, strength, power, and velocity were evaluated with concentric, isometric, isotonic, and eccentric muscle actions during a single-leg stance test and on single- and multi-joint dynamometers in 29 young (age = 21.45 ± 3.02) and 23 old (age = 77.00 ± 4.60) recreationally active men and women. Most (15 of 17) variables showed no statistical (p > 0.05) or functional (10% threshold) limb asymmetry for either age group. There was a significant main effect (p = 0.046; collapsed across groups) found for asymmetry (dominant > non-dominant) for the isotonic peak velocity variable. There was a significant (p = 0.010) group × limb interaction for single-joint concentric peak power produced at a slow (60 deg/s) velocity due to the non-dominant limb of the young group being 12.2% greater than the dominant limb (p < 0.001), whereas the old group was not asymmetrical (p = 0.965). The findings of this investigation indicate there is largely no age-related asymmetry of the lower limbs across a range of muscle function-related variables and modes, with a couple of notable exceptions. Also, the significant asymmetries for the isotonic peak velocity variable perhaps show the sensitivity of this uncommonly used measure in detecting minimally present muscle function imbalances.

Effects of Multi-joint Eccentric Training on Muscle Function When Combined With Aquatic Plyometric Training: A Minimal Dose, Mixed Training Study.

OBJECTIVES: To examine the effects of a combined eccentric overload and aquatic-based plyometric training program on muscle function/performance measures and soreness versus an eccentric-only training protocol using a minimal dose training paradigm. METHODS: Twenty-five participants were randomized into either an eccentric-only training group (ECC) or a combined eccentric and aquatic plyometric group (ECC + AQP). The ECC group performed eccentric training once per week for 6-weeks while the ECC + AQP group performed the same eccentric training but with an additional aquatic plyometric training session. RESULTS: There was no group × trial interactions for any of the variables. However, the training elicited large improvements in eccentric strength in both ECC (27%; ES = 1.33) and ECC+AQP (17%; ES = .86) groups. Isometric strength improved moderately for ECC and ECC+AQP groups (17.2%, ES = .53;9%, ES = .45). A moderate increase was observed for depth jump height for both ECC and ECC+AQP groups (13.1%, ES = .48;8.8%, ES = .36). No changes were observed for countermovement jump or sprint time and muscle soreness did not differ between groups. CONCLUSIONS: Minimal dose multi-joint eccentric overload training improved strength and depth jump outcomes after 6-weeks regardless of the training condition but adding a minimal dose aquatic plyometric protocol does not improve muscle function-based outcomes.

Test-retest reliability of the 5-minute psychomotor vigilance task in working-aged females.

BACKGROUND: The psychomotor vigilance task (PVT) is a commonly used test that effectively assesses neurobehavioral alertness. The originally developed PVT is 10 minutes in duration, which presents practical and logistical issues, particularly when administered to large samples or on a repetitive basis. More recently the PVT has been used in both 3- and 5-minute formats. While both of these durations have been shown to be field sensitive to identify impairments from sleep- and fatigue-related interventions, the 5-minute version has been suggested to be more valid than the 3-minute. However, while these have shown field-validity in a number of working populations, there is a paucity of data reporting the test-retest reliability statistics of the 5-minute PVT, particularly in working-aged females. The purpose of the study was to examine the test-retest reliability of a comprehensive set of PVT variables for the 5-minute PVT in a population of working-aged females (20-63 years). NEW METHOD: Participants reported to the laboratory on two separate days and performed a 5-minute PVT on each occasion. Outcome measures included the mean reaction time (MRT), fastest and slowest 10% of reaction times (F10RT% and S10RT%, respectively), standard deviation of reaction times (SDRT) as well as error-based metrics including major and minor lapses, anticipations, and false starts. In addition, total errors (ERR) were computed as a composite of all types of errors. Reliability statistics were reported as intraclass correlation coefficients (ICCs), standard error of measurement (SEM, SEM%), and minimal difference to be considered real (MD, MD%). Systematic error was also evaluated between sessions. RESULTS: Overall high reliability was shown for the MRT (ICC = 0.79, SEM% = 4.14%) and F10RT% (ICC = 0.83, SEM% = 4.43%) variables, with moderate relative reliability (based on ICCs) for the false starts, ERR, and sleepiness scale (ICC = 0.50 - 0.70) variables but these all exhibited poor absolute reliability (based on SEM% values of 32.60 - 168.69%). Poor relative reliability was found for the SDRT and S10RT% variables (ICCs < 0.50) but the S10RT% variable had good absolute reliability (SEM% = 7.12%). The minor and major lapses and anticipations variables had too few of event occurrences for a confident determination of the reliability. CONCLUSIONS: The finding that the MRT variable displayed systematic error (P = 0.01) indicating that a learning curve may have been present, but the F10RT% did not show systematic error, suggests the F10RT% may be the most reliable PVT variable in a 5-minute duration test. These findings provide researchers and practitioners with reliability statistics that may help in determining which variable(s) to use, and which to avoid when specifically conducting 5-minute PVT assessments, particularly in a population of working-aged females. These results suggest that the 5-minute PVT can be used in place of the 10-minute version, if used appropriately.

Biomechanical Comparison of Loaded Countermovement Jumps Performed on Land and in Water.

Louder, T, Bressel, E, Nardoni, C, and Dolny, D. Biomechanical comparison of loaded countermovement jumps performed on land and in water. J Strength Cond Res 33(1): 25-35, 2019-Researchers have observed physical improvements after the completion of aquatic-based jump training. However, there is a lack of research on the biomechanical specificity of aquatic-based movement. Therefore, the purpose of this investigation was to evaluate the kinetics and kinematics of loaded countermovement jumps performed in water versus land. Twenty young men and 24 National Collegiate Athletic Association (NCAA) Division I female soccer and gymnastics athletes were asked to perform unloaded and loaded countermovement jumps on land and in chest-deep water immersion. A triaxial force platform and 2-dimensional videography produced various kinetic and kinematic measures of jump performance. Peak and mean mechanical power outputs (W) were 88% (8,919 ± 3,744 vs. 4,734 ± 1,418 W; p < 0.001) and 81% (3,640 ± 1,807 vs. 2,011 ± 736 W; p < 0.001) greater for jumps performed in water vs. land. Peak dorsiflexion velocity was 688% faster (44 ± 39 vs. 5.6 ± 5.4 degree·s; p < 0.001) for jumps performed in water and tended to model similarly with measures of mechanical power and amortization rate. Body weight normalized peak and mean mechanical power outputs decreased by 23.6 ± 2.7 and 23.8 ± 1.9% when load was added in the water. The addition of load on land was associated with an 8.7 ± 2.3 and 10.5 ± 4.4% decrease in body weight normalized peak and mean mechanical power. Results suggest that the aquatic environment alters movement primarily at amortization and may provide a unique training stimulus. Also, it can be concluded that fluid resistance and buoyancy combine to influence the mechanics of jumping movements performed in the water.

Water Immersion Affects Episodic Memory and Postural Control in Healthy Older Adults.

BACKGROUND AND PURPOSE: Previous research has reported that younger adults make fewer cognitive errors on an auditory vigilance task while in chest-deep water compared with on land. The purpose of this study was to extend this previous work to include older adults and to examine the effect of environment (water vs land) on linear and nonlinear measures of postural control under single- and dual-task conditions. METHODS: Twenty-one older adult participants (age = 71.6 ± 8.34 years) performed a cognitive (auditory vigilance) and motor (standing balance) task separately and simultaneously on land and in chest-deep water. Listening errors (n = count) from the auditory vigilance test and sample entropy (SampEn), center of pressure area, and velocity for the balance test served as dependent measures. Environment (land vs water) and task (single vs dual) comparisons were made with a Wilcoxon matched-pair test. RESULTS: Listening errors were 111% greater during land than during water environments (single-task = 4.0 ± 3.5 vs 1.9 ± 1.7; P = .03). Conversely, SampEn values were 100% greater during water than during land environments (single-task = 0.04 ± 0.01 vs 0.02 ± 0.01; P < .001). Center of pressure area and velocity followed a similar trend to SampEn with respect to environment differences, and none of the measures were different between single- and dual-task conditions (P > .05). CONCLUSIONS: The findings of this study expand current support for the potential use of partial aquatic immersion as a viable method for challenging both cognitive and motor abilities in older adults.

Age-Related Changes in Postural Sway Are Not Consistent Between Land and Aquatic Environments.

BACKGROUND AND PURPOSE: Quantifying how the environment (land vs water) influences age-related changes in postural sway is important for the development of new therapies that improve balance. The authors are not aware of any previous studies that have compared postural sway in an aquatic environment between age groups or when water depth and/or perturbations are incorporated into the comparison. The purpose of this study was to compare the effect of water depth and jet intensity on postural sway in older and younger adults. METHODS: Sixteen older (age = 62.8 ± 9.56 years) and 15 younger (age = 22.5 ± 1.85 years) adults participated. Participants stood quietly for 90 seconds on land and at various water depths and jet intensities while center of pressure (CoP) sway was recorded using a force platform. RESULTS: Statistical comparisons revealed that CoP range and area measurements were different between land and aquatic conditions (P = .04 - .001). For example, CoP sway area in chest deep water (8.51 ± 2.97 cm) was greater than on land (2.41 ± 1.37 cm; effect size = 2.05). Furthermore, CoP sway area at the 60% jet intensity (71.4 ± 31.2 cm) was substantially greater than at the 20% jet intensity (12.4 ± 6.23 cm; effect size = 1.89). Surprisingly, the proportion of change across water depths and jet intensities was not consistent between older and younger groups as indicated by significant age by environment interactions (P = .03 - .001). Follow-up tests indicated that older adults swayed less than younger adults in water at the level of the hip (effect sizes = 0.42-0.94) and when water jets were applied at a 60% jet intensity (effect sizes = 0.63-1.97). CONCLUSIONS: Water immersion to the chest with high jet intensities produces the greatest CoP sway in both groups. This is likely a result of buoyancy and perturbation intensity. Less sway in the older group may reflect a strategy that reduces degrees of freedom for this group when faced with these stability challenges.

Acute and chronic effects of aquatic treadmill training on land treadmill running kinematics: A cross-over and single-subject design approach.

The aim of this study was to determine if selected kinematic measures (foot strike index [SI], knee contact angle and overstride angle) were different between aquatic treadmill (ATM) and land treadmill (LTM) running, and to determine if these measures were altered during LTM running as a result of 6 weeks of ATM training. Acute effects were tested using 15 competitive distance runners who completed 1 session of running on each treadmill type at 5 different running speeds. Subsequently, three recreational runners completed 6 weeks of ATM training following a single-subject baseline, intervention and withdrawal experiment. Kinematic measures were quantified from digitisation of video. Regardless of speed, SI values during ATM running (61.3 ± 17%) were significantly greater (P = 0.002) than LTM running (42.7 ± 23%). Training on the ATM did not change (pre/post) the SI (26 ± 3.2/27 ± 3.1), knee contact angle (165 ± 0.3/164 ± 0.8) or overstride angle (89 ± 0.4/89 ± 0.1) during LTM running. Although SI values were different between acute ATM and LTM running, 6 weeks of ATM training did not appear to alter LTM running kinematics as evidenced by no change in kinematic values from baseline to post intervention assessments.

Mechanical parameters and flight phase characteristics in aquatic plyometric jumping.

Plyometric jumping is a commonly prescribed method of training focused on the development of reactive strength and high-velocity concentric power. Literature suggests that aquatic plyometric training may be a low-impact, effective supplement to land-based training. The purpose of the present study was to quantify acute, biomechanical characteristics of the take-off and flight phase for plyometric movements performed in the water. Kinetic force platform data from 12 young, male adults were collected for counter-movement jumps performed on land and in water at two different immersion depths. The specificity of jumps between environmental conditions was assessed using kinetic measures, temporal characteristics, and an assessment of the statistical relationship between take-off velocity and time in the air. Greater peak mechanical power was observed for jumps performed in the water, and was influenced by immersion depth. Additionally, the data suggest that, in the water, the statistical relationship between take-off velocity and time in air is quadratic. Results highlight the potential application of aquatic plyometric training as a cross-training tool for improving mechanical power and suggest that water immersion depth and fluid drag play key roles in the specificity of the take-off phase for jumping movements performed in the water.

Effect of Water Immersion on Dual-task Performance: Implications for Aquatic Therapy.

BACKGROUND AND PURPOSE: Much is known about cardiovascular and biomechanical responses to exercise during water immersion, yet an understanding of the higher-order neural responses to water immersion is unclear. The purpose of this study was to compare cognitive and motor performance between land and water environments using a dual-task paradigm, which served as an indirect measure of cortical processing. DESIGN: A quasi-experimental crossover research design is used. METHODS: Twenty-two healthy participants (age = 24.3 ± 5.24 years) and a single-case patient (age = 73) with mild cognitive impairment performed a cognitive (auditory vigilance) and motor (standing balance) task separately (single-task condition) and simultaneously (dual-task condition) on land and in chest-deep water. Listening errors from the auditory vigilance task and centre of pressure (CoP) area for the balance task measured cognitive and motor performance, respectively. RESULTS: Listening errors for the single-task and dual-task conditions were 42% and 45% lower for the water than land condition, respectively (effect size [ES] = 0.38 and 0.55). CoP area for the single-task and dual-task conditions, however, were 115% and 164% lower on land than in water, respectively, and were lower (≈8-33%) when balancing concurrently with the auditory vigilance task compared with balancing alone, regardless of environment (ES = 0.23-1.7). This trend was consistent for the single-case patient. CONCLUSION: Participants tended to make fewer 'cognitive' errors while immersed chest-deep in water than on land. These same participants also tended to display less postural sway under dual-task conditions, but more in water than on land. Copyright © 2015 John Wiley & Sons, Ltd.