Isaac Selva Raj

Aging and the force-velocity relationship of muscles.

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

Effects of eccentrically biased versus conventional weight training in older adults.

INTRODUCTION We compared the effects of eccentrically biased (EB) and conventional (CONV) resistance training on muscle architecture, one-repetition maximum (1RM), isometric strength, isokinetic force-velocity characteristics, functional capacity, and pulse wave velocity in older men and women. METHODS Twenty-eight older adults participated in the study (mean ± SD: age = 68 ± 5 yr). Of these, 13 were allocated to a waitlist control, 10 of whom progressed to training (CONV, n = 12; EB, n = 13). Training was twice a week for 16 wk. EB involved three sets of 10 concentric lifts at 50% of 1RM with the eccentric portion of repetitions performed unilaterally, alternating between limbs with each repetition. CONV involved two sets of 10 repetitions at 75% of 1RM. EB and CONV were matched for total work. Isokinetic knee extensor strength was assessed across a range of velocities (0-360°·s(-1)). Functional capacity was assessed via a 6-m fast walk test, a timed up and go test, stair climb and descent power test, and vertical jump test. Vastus lateralis and gastrocnemius medialis architecture were assessed using ultrasonography. RESULTS Both EB and CONV improved 1RM (Δ 23%-35%, P < 0.01). Compared to the control group, both training regimens improved 6-m fast walk (Δ 5%-7%, P < 0.01) and concentric torque at 60 and 120°·s(-1) (Δ 6%-8%, P < 0.05). Significant improvements were evident in EB for isometric and concentric torque at 240 and 360°·s(-1) (Δ 6%-11%, P < 0.05), vastus lateralis thickness (Δ 5%, P < 0.05), and stair climb (Δ 5%, P < 0.01). Timed up and go (Δ 5%, P < 0.01), stair descent (Δ 4%, P < 0.05), and vertical jump (Δ 7%, P < 0.01) improved in CONV. Pulse wave velocity, pennation angle, and fascicle length remained unchanged in both training groups. CONCLUSIONS EB seems superior to CONV at increasing torque at high contraction velocities, whereas CONV seems more effective at improving some functional performance measures and vertical jump. This has important implications for preserving functional capacity.

Reliability of ultrasonographic measurement of the architecture of the vastus lateralis and gastrocnemius medialis muscles in older adults

Objective:  To determine the test‐retest reliability of measurements of thickness, fascicle length (Lf) and pennation angle (θ) of the vastus lateralis (VL) and gastrocnemius medialis (GM) muscles in older adults.

Validation of the Fitbit One, Garmin Vivofit and Jawbone UP activity tracker in estimation of energy expenditure during treadmill walking and running

Abstract Objectives: To determine the validity of energy expenditure estimation made by the Fitbit One, Garmin Vivofit and Jawbone UP activity trackers during treadmill walking and running. Determining validity of such trackers will inform the interpretation of the data they generate. Design: Cross-sectional study. Method: Fourteen adults walked at 0.70, 1.25, 1.80 ms−1 and ran at 2.22, 2.78, 3.33 ms−1 on a treadmill wearing a Fitbit One, Garmin Vivofit and Jawbone UP. Estimation of energy expenditure from each tracker was compared to measurement from indirect calorimetry (criterion). Paired t-tests, correlation coefficients and Bland–Altman plots assessed agreement and proportional bias. Mean percentage difference assessed magnitude of difference between estimated and criterion energy expenditure for each speed. Results: Energy expenditure estimates from the Fitbit One and Garmin Vivofit correlated significantly (p< 0.01; r= 0.702; 0.854) with criterion across all gait speeds (0.70–3.33 ms−1). Fitbit One, Garmin Vivofit and Jawbone UP correlated significantly (p < 0.05; r = 0.729; 0.711; 0.591) with criterion across all walking speeds (0.70–1.80 ms−1). However, only the Garmin Vivofit correlated significantly (p< 0.05; r = 0.346) with energy expenditure estimations from criterion across running speeds (2.22–3.33 ms−1). Bland–Altman plots showed proportional bias for the Fitbit One and Garmin Vivofit. Energy expenditure estimations of single speeds were overestimated by the Fitbit One and underestimated by the Garmin Vivofit. Conclusions: Energy expenditure reported by the devices distinguished between walking and running, with a general increase as exercise intensity increased. However, the reported energy expenditure from these devices should be interpreted with caution, given their potential bias and error. Practical implications Although devices report the same outcome of EE estimation, they are not equivalent to each other and differ from criterion measurements during walking and running. These devices are not suitable as research measurement tools for recording precise and accurate EE estimates but may be suitable for use in interventions of behaviour change as they provide feedback to user on trends in energy expenditure. If intending to use these devices in studies where precise measurements of energy expenditure are required, researchers need to undertake specific validation and reliability studies prior to interventions and the collection of cross-sectional data.

Light physical activity is positively associated with cognitive performance in older community dwelling adults

OBJECTIVES To evaluate the associations between an objective measure of different intensities of physical activity, upper- and lower-limb muscle strength and psychomotor performance and set-shifting domains of cognitive executive function in older adults. DESIGN A cross-sectional study. METHODS From the Tasmanian Older Adult Cohort Study, 188 community-dwelling older adults (53.7% female; mean age±SD 63.98±7.3 years) undertook 7-day physical activity behaviour monitoring using an accelerometer. Dynamometers were used to assess leg extension strength. The Trail Maker Tests were used to measure psychomotor processing speed and set-shifting performance. RESULTS When controlling for age, smoking history, alcohol intake, educational achievement and neuropsychological functioning, higher levels of light physical activity, but not sedentary behaviour or moderate or vigorous physical activity, was found to be associated with better set-shifting performance. Neither physical activity behaviour or muscle strength were found to be associated with psychomotor performance. In addition, older age, greater alcohol intake, and lower levels of educational attainment, verbal learning and memory performance were significantly associated with lower scores on the set-shifting task; whereas older age and reduced neuropsychological functioning were associated with lower psychomotor processing speed scores. CONCLUSIONS Light physical activity is associated with higher executive functioning in community-dwelling older adults and this strengthens the evidence supporting exercise as a neuroprotective agent. Further studies are needed to understand why light physical activity behaviour positively influences executive functioning, and how such physical activity can be implemented into the daily routine of older adults.

Determining Criteria to Predict Repeatability of Performance in Older Adults: Using Coefficients of Variation for Strength and Functional Measures

Reliable measures of muscle strength and functional capacity in older adults are essential. The aim of this study was to determine whether coefficients of variation (CVs) of individuals obtained at the first session can infer repeatability of performance in a subsequent session. Forty-eight healthy older adults (mean age 68.6 ± 6.1 years; age range 60-80 years) completed two assessment sessions, and on each occasion undertook: dynamometry for isometric and isokinetic quadriceps strength, 6 meter fast walk (6MFWT), timed up and go (TUG), stair climb and descent, and vertical jump. Significant linear relationships were observed between CVs in session 1 and the percentage difference between sessions 1 and 2 for torque at 60, 120, 240 and 360°/s, 6MFWT, TUG, stair climb, and stair descent. The results of this study could be used to establish criteria for determining an acceptably reliable performance in strength and functional tests.