Fat-free mass mediates the association between body mass and jump height in healthy young adults.

BACKGROUND: The countermovement jump (CMJ) is a reliable and valid test of lower-extremity (LE) muscle power and neuromuscular performance. Body mass is positively associated with CMJ performance in young adults, warranting the examination of the influence of body composition on jump height (JH). This study examined the mediation effects of body composition on CMJ performance in young adults. The hypothesis was that fat-free mass and percent fat mass would significantly mediate the association between body mass with JH in young adults. METHODS: Healthy young adults (N.=81; 47 female; mean age 25.1±3.4) completed this study and underwent body composition assessment using a bioelectrical impedance analysis device. Participants performed three CMJ trials to measure average JH using an electronic jump mat. Mediation analysis models were performed to examine the hypothesis of this study. RESULTS: The mediation analyses indicated that the indirect effects of fat-free mass on the association between body mass with JH were significant (indirect effect [IE]=-0.23, 95% CI -0.315, 0.767; IE=0.76, 95% CI 0.334, 1.272; respectively), after controlling for sex and percent fat mass. CONCLUSIONS: The association between body mass with JH in young adults with normal BMI was mediated by fat-free mass. Clinicians, trainers, and coaches should potentially target increasing fat-free mass when improving LE power and neuromuscular performance in rehabilitation and sports settings in this population, but further studies are needed.

Enhancement of Muscle Shortening Torque Preloaded with Muscle Lengthening is Joint-Specific.

Our cross-sectional study aimed to investigate joint specificity of concentric muscle torque enhancement after a maximum eccentric contraction for the knee versus ankle joints across two different movement velocities (120°/s and 180°/s). After a familiarization session, 22 healthy young adults randomly performed concentric (CONC) and maximum eccentric preloaded concentric (EccCONC) muscle strength tests of the knee extensors and ankle plantar flexors of the non-dominant leg on an isokinetic strength testing device. We calculated the ratio between EccCONC and CONC (EccCONC/CONC) for all the conditions as the marker of concentric muscle torque enhancement. Separate two-way (joints x velocity) within repeated measures ANOVAs were used to determine joint-specific torque differences at 120°/s and 180°/s. CONC and EccCONC were greater for the knee extensors versus ankle plantar flexors at 120°/s and 180°/s (32.86%-102%; p < 0.001 for both); however, EccCONC/CONC was greater for the ankle plantar flexors than knee extensors at 120°/s (52.4%; p < 0.001) and 180°/s (41.9%; p < 0.001). There was a trend of greater EccCONC/CONC for the knee extensors at 180°/s than 120°/s (6.6%; p = 0.07). Our results show that greater concentric muscle torque enhancement after a maximal eccentric contraction occurs for the ankle plantar flexors versus knee extensors. Whether the joint- specificity of concentric muscle torque enhancement after a maximal eccentric contraction differentially affects sports performance is unknown. Our data provide a reference framework to investigate joint-specific concentric muscle torque enhancement for general and clinical athletic populations.

Effects of backward walking exercise using lower body positive pressure treadmill on knee symptoms and physical function in individuals with knee osteoarthritis: a protocol for RCT.

OBJECTIVES: The primary aim is to compare the effects of backward walking exercise to forward walking exercise on knee pain, knee functions, and thigh muscle strength in individuals with mild to moderate knee osteoarthritis using lower body positive pressure, in addition to mobility functions, balance, and self-reported health status. METHODS: The study is a single blind randomized clinical trial with two independent groups. This study will enroll 26 participants with mild to moderate knee osteoarthritis. The participants will be randomized into either experimental group (backward walking exercise) or control group (forward walking exercise). Both groups will use lower body positive pressure treadmill for walking exercise. Both groups will perform regular conventional exercise and worm-up exercise before walking exercise. The treatment will be three times a week for six weeks. Walking session will be up to 30 min each session. Data collection will be collected during pre- and post- intervention including primary outcomes including numeric pain rating scale (NPRS), knee injury and osteoarthritis outcome score (KOOS), and thigh muscle strength test. The secondary outcomes include five times sit to stand test (FTSTS), 3-meter backward walk test (3MBWT), timed up and go test (TUG), four square step test (FSST), functional reach test (FRT), 10-meter walk test (10-MWT), six minute walk test (6MWT), medical outcomes study short form 12 (SF-12), patient health questionnaire -9 (PHQ-9), and rapid assessment of physical activity (RAPA). An independent t-test will be used to evaluate the effect of treatment on the outcome measures. RESULTS: Not applicable. CONCLUSION: Using lower body positive pressure may have promising results against knee osteoarthritis. Moreover, walking backward exercise using lower body positive pressure might add more benefits to individuals with knee osteoarthritis and help clinicians in decision making. TRIAL REGISTRATION: This study was registered in ClinicalTrails.gov (ID: NCT05585099).

The Safety and Feasibility of Lower Body Positive Pressure Treadmill Training in Individuals with Chronic Stroke: An Exploratory Study.

BACKGROUND: Lower body positive pressure (LBPP) may provide a novel intervention for gait training in neurological conditions. Nonetheless, studies investigating the safety and feasibility of LBPP in patients with stroke are insufficient. OBJECTIVES: The purpose of this study was to evaluate the safety and feasibility of LBPP as a rehabilitation intervention for individuals with chronic stroke. METHODS: Individuals with chronic stroke were recruited from the community to participate in LBPP gait training three times a week for six weeks. The LBPP's safety and feasibility were documented throughout the study and at the end of six weeks. Safety and feasibility referred to the incidence of adverse events, complications, the participant and therapist satisfaction questionnaire, and the device limitation including but not limited to technical issues and physical constraints. In addition, blood pressure, pulse rate, and oxygen saturation were taken pre- and post-session. Dependent t-tests were used to analyze the difference between assessments. A Wilcoxon test was used to assess the ordinal data (Trial registration number NCT04767334). RESULTS: Nine individuals (one female, eight males) aged 57 ± 15.4 years were enrolled. All participants completed the intervention without adverse events. All participants reported positive scores from 4 (very satisfying) to 5 (extremely satisfying) in the safety and feasibility questionnaire. No significant differences were observed in blood pressure and oxygen saturation during the intervention sessions. However, significant increases were observed in heart rate from 82.6 ± 9.1 beats/min (pre-session) to 88.1 ± 6.8 beats/min (post-session) (p = 0.027). CONCLUSIONS: LBPP is a safe and feasible rehabilitation tool to use with individuals with chronic stroke.

Joint specificity of stretch shortening cycle potentiation at propulsion onset during jump test performance.

BACKGROUND: Joint specific stretch-shortening cycle (SSC) potentiation of lower extremity joints at propulsion onset during jump test performance (JTP) can temporally affect SSC potentiation. However, joint-specific SSC potentiation at propulsion onset during JTP is unknown. METHODS: Twenty-two healthy young adults, 12 men and 10 women, performed: vertical jumps (1) with a preliminary countermovement (CMJ), 2) from a squat position held isometrically for 2-3 seconds at the same knee angle of CMJ (SJ), and (3) after landing from a 15 cm high platform (DJ). Kinetics and kinematics of lower extremity joints were collected. The propulsion onset was calculated uniquely for the hip, knee, and ankle joints and defined as the first positive data point (after the eccentric phase) of the joint angular velocity for each respective joint. SSC potentiation was calculated as the ratio of jump height (JH) and joint extensor moments for CMJ/SJ, DJ/SJ, and DJ/CMJ. RESULTS: JH ratio for CMJ/SJ, DJ/SJ, and DJ/CMJ were >1 (all P< 0.01). Hip, knee, and ankle extensor moment ratio was >1 (all P<0.01) for CMJ/SJ and DJ/SJ, while for DJ/CMJ, extensor moment ratio was >1 only for the ankle (P<0.03). SSC potentiation was greatest at the ankle followed by the hip and knee for CMJ/SJ and DJ/SJ (all P<0.05). CONCLUSIONS: SSC potentiation at propulsion onset was largest at the ankle followed by hip and knee. Our findings emphasize the importance of the ankle versus hip and knee joints regarding SSC potentiation at the very beginning of JTP.

30-Second Chair Stand Test Predicts Countermovement Jump Performance in Young Adults.

BACKGROUND: The countermovement jump (CMJ) is a valid and reliable test of lower extremity (LE) muscle power. However, the CMJ may not be appropriate during early-stage rehabilitation of injuries. Functional muscle strength tests (FMSTs) could evaluate LE muscle power with lower joint reaction forces. HYPOTHESIS: The lateral step-up test (LSUT), 5 times sit to stand (5×STS), and 30-s chair stand test (30CST) could predict CMJ jump height (JHt) and jump peak power (JPow). STUDY DESIGN: Cross-sectional study. LEVEL OF EVIDENCE: Level 2. METHODS: Eighty-one young adults performed 3 CMJs to measure JHt and JPow using an electronic jump mat and speed analyzer. Participants also performed three FMSTs: 1 trial of the LSUT and a modified trial of LSUT touching the ground with the heel only (MLSUT); 2 trials of the 5×STS; and 2 trials of the 30CST, in a randomized order. Spearman rho correlations and hierarchal multiple linear regressions were used to determine whether FMST performances predicted JHt and JPow, after controlling for sex, body height, and body mass. RESULTS: 30CST, LSUT, MLSUT, sex, body mass, and body height were significantly associated with JHt (P < 0.05). LSUT, sex, body height, and body mass were significantly associated with JPow (P < 0.05). Hierarchical regression analyses showed that the 30CST significantly predicted JHt (P < 0.01) and JPow (P = 0.03), independent of sex, body height, and body mass. CONCLUSION: 30CST performance predicted JHt and JPow in young adults. CLINICAL RELEVANCE: The 30CST is easy to perform, requires equipment found readily in clinics, and predicts LE muscle power. This test could be used to track progress during the early stages of LE injury rehabilitation.