Dain Patrick LaRoche

Lifting during manual material handling is a major cause of low-back pain (LBP). As an important risk factor that directly influences the risk of LBP, the Load vertical location (LVL) during lifting needs to be measured and controlled. However, existing solutions for LVL measurement are inefficient, inaccurate, and impractical for real-world workplace environments. To address these problems, an unobtrusive wearable system, including smart insoles and smart wristbands, was proposed to measure LVL accurately in workplace environments. Different from traditional methods, which rely on Inertial Measurement Unit (IMU) and suffer from integral drifting errors over time, a novel barometer-based LVL measurement method was proposed in this study. To correct environment-induced LVL measurement errors in the barometer-based method, a novel Known Vertical Location Update (KVLU) method was proposed. This method automatically calibrates the measured LVL using known wrist vertical location at reference points, which can be detected by the proposed wearable system during frequently-used working activities such as standing and walking. The proposed wearable system achieved a mean absolute error (MAE) of 5.12 cm and 5.68 cm in LVL measurement using personalized and generic reference points, respectively, which demonstrates its reliable performance for LVL estimation.

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.

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.

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 (Cw_kg) 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). Cw_kg wasn’t different between NW or OB, but there was a negative correlation between BMI and Cw_kg driven by lower Cw_kg in NWL. Cw and K_vert covaried in proportion to body mass, but mass-specific K_vert was unrelated to Cw_kg. 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.

This study compared functional demand (FD) between older and younger women walking at habitual and fast speed and determined strength thresholds necessary to maintain FD below 80%. FD was calculated by expressing walking flexion and extension joint torques, of the ankle, knee, and hip, as a percentage of maximal strength. Young had an average FD of 65% across joint actions and speeds, whereas older women had FD of 90%. In older women the greatest FD occurred in the hip musculature. The hip, knee and ankle extensor strengths required to maintain FD below 80% were 1.66, 1.86 and 0.57 Nm.kg-1, and flexor strengths were 1.24, 0.49 and 0.69 Nm.kg-1, respectively. Older women have limited functional reserve to increase gait speed and rely heavily on available hip strength during walking. This study identifies strength targets for the hip, knee, and ankle that will assist in maintaining FD of older women at a sustainable level.