Added body mass alters plantar shear stresses, postural control, and gait kinetics: Implications for obesity

Context Obesity is a growing global health concern. The increased body mass and altered mass distribution associated with obesity may be related to increases in plantar shear that putatively leads to physical functional deficits. Therefore, measurement of plantar shear may provide unique insights on the effects of body mass and body distribution on physical function or performance. Purpose 1) To investigate the effects of body mass and distribution on plantar shear. 2) To examine how altered plantar shear influences postural control and gait kinetics. Hypothesis 1) a weighted vest forward distributed (FV) would shift the center of pressure (CoP) location forward during standing compared with a weighted vest evenly distributed (EV), 2) FV would increase plantar shear spreading forces more than EV during standing, 3) FV would increase postural sway during standing while EV would not, and 4) FV would elicit greater compensatory changes during walking than EV. Methods Twenty healthy young males participated in four different tests: 1) static test (for measuring plantar shear and CoP location without acceleration, 2) bilateral-foot standing postural control test, 3) single-foot standing postural test, and 4) walking test. All tests were executed in three different weight conditions: 1) unweighted (NV), 2) EV with 20% added body mass, and 3) FV, also with 20% added body mass. Plantar shear stresses were measured using a pressure/shear device, and several shear and postural control metrics were extracted. Repeated measures ANOVAs with Holms post hoc test were used to compare each metric among the three conditions (α = 0.05). Results FV and EV increased both AP and ML plantar shear forces compared to NV. FV shifted CoP forward in single-foot trials. FV and EV showed decreased CoP range and velocity and increased Time-to-Boundary (TTB) during postural control compared to NV. EV and FV showed increased breaking impulse and propulsive impulse compared to NV. In addition, EV showed even greater impulses than FV. While EV increased ML plantar shear spreading force, FV increased AP plantar shear spreading force during walking. Conclusion Added body mass increases plantar shear spreading forces. Body mass distribution had greater effects during dynamic tasks. In addition, healthy young individuals seem to quickly adapt to external stimuli to control postural stability. However, as this is a first step study, follow-up studies are necessary to further support the clinical role of plantar shear in other populations such as elderly and individuals with obesity or diabetes.

Influence of Self-managed Rehabilitation on Work Efficiency in Active Duty Military With a Knee Injury

Introduction Knee injuries associated with intense physical training are one of the most frequent injuries associated with medical encounters for military members. The purpose of this study was to evaluate four approaches to physiotherapy rehabilitation and their effects on work efficiency in active duty military with a knee injury. The four groups included neuromuscular electrical stimulation (NMES), walking with a weighted vest (WALK), combined NMES/Walk, and standard physiotherapy rehabilitation. All groups received standard physiotherapy rehabilitation. We have previously reported that quadriceps muscle strength improved over 18 weeks in the study for the three interventions relative to standard rehabilitation alone. This report presents results from an examination of work efficiency as evaluated during a step test while measuring oxygen utilization. Methods A randomized controlled trial was conducted, with repeated outcome measures of work efficiency assessed at baseline, 3, 6, 12, and 18 weeks. The sample consisted of 67 active duty service members between the ages of 18 and 50 years with a knee injury. Participants were randomized to one of the four approaches to physiotherapy rehabilitation: (1) NMES was applied to the quadriceps muscle four times per week, for 30 minutes (15 minutes to each leg), consisting of 15 quadriceps muscle contractions per leg; (2) graduated strength walking using a weighted vest (WALK) was for 30 minutes, 3 to 4 days a week; (3) combined NMES with strength walking received both the NMES therapy and the weighted vest walking; and (4) standard physiotherapy consisted of progressive exercise with the number and type of sessions not controlled by the study. All four groups received the standard physiotherapy for a knee injury. The primary outcome was work efficiency, as measured by oxygen utilization during a 2-minute self-paced step test over 18 weeks. The primary analysis used repeated measures, linear mixed-effects models with a random effect for subject. Results Both the number of steps performed and gross work efficiency improved during the study for all three intervention groups. For gross work efficiency, standard rehabilitation improved 12%, WALK showed a 19% improvement, NMES increased by 24%, and the NMES/Walk group improved by 40%. Conclusions All groups showed improved submaximal exercise efficiency based on oxygen utilization, with the intervention groups showing a greater improvement in work efficiency as compared to standard rehabilitation. Knee injuries can be problematic for active duty members because of reduced mobility leading to deconditioning and associated declines in work efficiency. Rehabilitative programs, including those described in this study, may minimize loss of work efficiency and fitness and promote a quicker recovery.

The Effects of Lateral Bounds on Post-Activation Potentiation of Change-of-Direction Speed Measured by the 505 Test in College-Aged Men and Women

Forty recreationally-trained individuals completed four testing sessions to determine whether lateral bounds (LB) or weighted lateral bounds enhanced change-of-direction (COD) speed measured by the 505 COD speed test. Session 1 included vertical jump and lateral bound (LB) testing to measure power. Sessions 2–4 involved three randomized conditioning activities (CA): 3 × 5 LB; 3 × 5 weighted LB (10% body mass provided by a weighted vest); and a control condition (4-min rest). The 505 COD speed test was performed 5- and 2.5-min pre-CA, and ~15 s, 4, 8, 12, and 16 min post-CA. A 3 × 6 repeated measures analysis of variance (ANOVA) calculated performance changes across time points post-CA. A 3 × 2 repeated measures ANOVA analyzed best potentiated performance. Smallest worthwhile change (SWC) measured within-subject 505 COD speed test performance. Partial correlations controlling for sex calculated relationships between the vertical jump, LB, and percent potentiation. There were no differences (p = 0.919) in 505 time relative to baseline for any CA, nor was the SWC exceeded. The best potentiated 505 time was faster (p < 0.001) than baseline for all CA, with no between-CA differences. There were no significant (p = 0.056–0.993) correlations between power and potentiation. LB and weighted LB did not potentiate the 505 COD speed test, although performance was not hindered.

Effects of Weighted Vest Loading During Daily Living Activities on Countermovement Jump and Sprint Performance

Purpose: Wearing a weighted vest (WV) during daily living and training can enhance jump and sprint performance; however, studies examining the efficacy of this method in female populations is limited. This study examined the effect of wearing a WV during daily living and training on countermovement jump (CMJ), change-of-direction, and sprint performance. Methods: Trained females were separated into intervention (n = 9) and control (n = 10) groups. The intervention group wore WVs of ∼8% body mass 4 days per week for 8 hours per day (32 h/wk total), and 3 training sessions per week for the first 3 weeks. Subsequently, 3 weeks of regular training without WV stimulus was completed. The control group received no intervention and continued normal training for 6 weeks. Average and best performance was assessed on the single CMJ, four continuous CMJ, t-test change-of-direction drill, and a 25-m sprint at baseline, week 3, and week 6. Results: No significant interactions or group effects were found. However, significant time main effects revealed increases in average rate of force development during the CMJ from baseline to week 3 (P = .048) and week 6 (P = .013), whereas peak vertical ground reaction force increased during the four continuous CMJ from baseline to week 3 (P = .048) and week 6 (P = .025) for both groups. Conclusions: The lower relative WV load used in this study failed to elicit significant improvements in jump and sprint performance in comparison with routine training, or that which have been found in past investigations with elite male athletes completing high-intensity performance tasks with greater WV loads.

Dynamic Warm-Up With a Weighted Vest: Improvement of Repeated Change-of-Direction Performance in Young Male Soccer Players

Purpose: To explore the effect of 4 different warm-up strategies using weighted vests and to determine the specific optimal recovery duration required to optimize the repeated change-of-direction (RCOD) performance in young soccer players. Methods: A total of 19 male soccer players (age 18 [0.88] y, body mass 69.85 [7.68] kg, body height 1.75 [0.07] m, body mass index 22.87 [2.23] kg·m−2, and body fat percentage 12.53% [2.59%]) completed the following loaded warm-up protocols in a randomized, counterbalanced cross-over, within-participants order and on separate days: weighted vest with a loading of 5% (WUV5%), 10% (WUV10%), 15% (WUV15%) body mass, and an unloaded condition (control). RCOD performance (total time, peak time, and fatigue index) was collected during the preintervention phase (5 min after the dynamic stretching sequence) for baseline values and immediately (at 15 min), at 4- and 8-minute postwarm-up intervention. Results: For each postwarm-up tested, recovery times (ie, 15 s, 4 min, and 8 min), of both total and peak times were faster following WUV5%, WUV10%, and WUV15%, compared with the unloaded condition (P ≤.001–.031, d = 1.28–2.31 [large]). There were no significant differences (P = .09–1.00, d = 0.03–0.72 [trivial–moderate]) in-between recovery times in both total and peak times following WUV5%, WUV10%, and WUV15%. However, baseline fatigue index score was significantly worse than all other scores (P ≤.001–.002, d = 1.35–2.46 [large]) following the loaded conditions. Conclusions: The findings demonstrated that a dynamic loaded warm-up increases an athlete’s initial RCOD performance up to the 8-minute postwarm-up intervention. Therefore, strength coaches need to consider using weighted vests during the warm-up for trained athletes in order to acutely optimize RCODs.