Nagai, Takashi

Background Following anterior cruciate ligament (ACL) injury, many athletes that undergo surgery and 6–9 months of rehabilitation struggle to return to sport. Evidence suggests that psychological factors contribute to this failure to return-to-sport. Objective Determine the motor control relationship between thigh musculature motor unit characteristics and psychological readiness to return to sport between ACL-injured and healthy controls. Study design A longitudinal cohort study. Methods Athletes longitudinally completed the ACL Return to Sport after Injury (ACL-RSI) survey and isometric strength measures with a measurement of electromyography (EMG) of the vastus lateralis, vastus medialis, biceps femoris, and semitendinosus. A score cut-off of 61 on the ACL-RSI was used to divide ACL-injured groups. EMG was decomposed to provide each identified motor unit’s characteristics (amplitude, average firing rate, etc). Results Data demonstrated increased average firing rate for hamstrings (p<0.001), decreased average firing rate for vastus lateralis (p<0.001) and decreased motor unit size for both the quadriceps and hamstrings at return-to-sport post-ACL reconstruction compared with sex-matched and age-matched healthy controls (p<0.001). Furthermore, there were marked differences in disparate ACL-RSI scores between ACL-injured athletes. Conclusions At return to sport, ACL-injured athletes have major alterations of thigh musculature motor control, with smaller motor units used by those with low ACL-RSI scores. This study uniquely demonstrates objective thigh muscle motor unit characteristics that coincide with subjective reports of psychological readiness. This information will be important to address psychomotor complexes of injury for future rehabilitation protocols.

Introduction: Physical activity is protective against cardiovascular (CV) disease and mortality, yet more than 25% of adults do not perform any regular exercise. Whole body electronic muscle stimulation (WB-EMS) is a novel FDA-approved device used for physical training that simultaneously stimulates all major muscle groups using percutaneous electrical impulse transmission during exercise. Preliminary studies demonstrated increased muscle mass, reduced fat mass, and improved functional capacity in elderly individuals who trained with WB-EMS. We evaluated the effects of training with WB-EMS on measures of CV health. Methods: Healthy adults were randomized to physical training with versus without WB-EMS for one 20-minute session each week for 16 weeks. Participants wore a specifically designed vest and arm and leg straps connected to the WB-EMS device (Miha Bodytec, Germany). Biphasic electrical stimulation was delivered through the vest and straps (4 sec on, 4 sec off) at a frequency that elicited a score of 5-6 on the Borg perceived exertion scale when each major muscle group was stimulated. Individuals randomized to no WB-EMS wore the same equipment but received no stimulation. Sessions were provided by trainers certified in WB-EMS training and consisted of a fixed protocol of simple exercises such as squats and lunges. Temporal changes in measures of CV health were compared between groups. Results: Forty-one individuals were recruited between 02/2021 and 02/2022 (n=24 WB-EMS, n=17 no WB-EMS; mean age 35.9±11.2 yrs; 61.3% females; median BMI 24.3 (21.8, 28.1) kg/m 2 . After 16 weeks there were significant and favorable differences in the intervention group compared to controls in waist: hip ratio (-1.2 cm vs. 0.9, p=0.05); total cholesterol (-1.1 mg/kg vs. 14.2 mg/kg, p=0.02); anaerobic threshold (68.2% vs. 30.8%, p=0.03); breathing efficiency (VE/VCO2: -10.36 vs -7.38, p=0.01); and peripheral endothelial function, measured with reactive hyperemia peripheral arterial tonometry (-0.009 vs. -0.29, p=0.06). Conclusions: Once weekly training with WB-EMS yielded more favorable changes in CV biomarkers compared to conventional training alone in healthy adults, and thus may offer an effective and time-efficient method of physical training.

Background Previous literature has postulated a relationship between greater hamstring stiffness and a higher risk of sustaining injury. Shear wave elastography (SWE) presents a relatively new means for non-invasive evaluation of soft tissue elasticity pre- and post- injury or intervention. Purpose 1. (1) To establish baseline hamstring stiffness measures for young competitive athletes and (2) determine effect of targeted neuromuscular training (TNMT) on shear wave stiffness of the hamstring. Study Design Un-blinded, prospective, non-randomized, cohort study. Methods Six-hundred forty-two lower extremities from 321 high school and collegiate basketball athletes (177 F: 139 M) were examined for hamstring stiffness prior to the start of their competitive basketball season. Teams were cluster assigned to either the control or intervention (TNMT) group. Subjects in the control group underwent regular season activities as directed, with no influence from the research team. For the TNMT group, the research team introduced a hamstring targeted dynamic warm-up program as an intervention focused on activating the hamstring musculature. Results Collegiate status was significant to hamstring stiffness for both sexes (p ≤ 0.02), but hamstring stiffness did not correlate to age or sex (r 2 ≤ 0.08). Intervention was a significant factor to hamstring stiffness when the hip was positioned in extension (p ≤ 0.01), but not in deeper flexion (p = 0.12). This effect was sex-specific as TNMT influenced hamstring stiffness in females (p = 0.03), but not in males (p ≥ 0.13). Control athletes suffered three HAM injuries; TNMT athletes suffered 0 hamstring injuries. Conclusion Higher SWE measurements correlated with increased risk of injury, male sex, and collegiate athletics. TNMT intervention can lessen muscle stiffness which may reduce relate to injury incidence. Intervention effectiveness may be sex specific. Level of Evidence II

Consistent differences between males and females have been shown in land-based measurements of anaerobic power and capacity. However, these differences have not been investigated for a tethered 30-s maximal swimming test (TST). The purpose of this study is to explore gender differences in land and pool-based assessments of anaerobic power (Fpeak) and capacity (Fmean), as well as the influence of body composition. Thirteen males and fifteen females completed land (Wingate (WAnT)) and pool-based (TST) measures of anaerobic power and capacity previously described in the literature. Additionally, the subjects completed assessments of body composition via air displacement plethysmography. The males produced higher force than the females for Fpeak (p < 0.001) and Fmean (p = 0.008) during the TST. However, linear regression analysis determined that lean mass significantly predicted Fpeak (p = 0.002) and Fmean (p < 0.001) during the TST, while gender was no longer significant (p = 0.694 and p = 0.136, respectively). In conclusion, increases in anaerobic power and capacity (Fpeak and Fmean) may be a function of increased lean mass in males and females, warranting future research on the impact of resistance training programs on force production and swimming performance.

ABSTRACTJoint trauma induces a presynaptic reflex inhibition termed arthrogenic muscle inhibition (AMI) that prevents complete activation of muscles. Reduced motor unit (MU) output is a hypothesised mechanism for persistent strength deficits. The objective of this study was to determine MU characteristics of thigh musculature and determine how they change with anterior cruciate ligament (ACL) injury compared to healthy controls. A randomised protocol of knee flexion/extension isometric contractions (10–50% maximal voluntary isometric contraction) was performed for each leg with surface EMG 5‐pin array electrodes placed on the vastus medialis, vastus lateralis, semitendinosus and biceps femoris. Longitudinal assessments for average rate coding, recruitment thresholds and MU action potentials were acquired at 6‐month intervals. With exception of the vastus medialis, all thigh musculature of ACL‐injured demonstrated smaller MU action potential peak‐to‐peak amplitude. For average rate coding, ACL‐injured demonstrated lower coding rates than Controls for the quadriceps (p < .05) and higher rates than Controls for the hamstrings (p < .05). These MU characteristics were different from Controls after ACL reconstruction up to 12 months post‐surgery, yet maximal strength increased during this time frame. As thigh MU characteristics are known across phases of ACL rehabilitation, future studies can assess these patterns of motor control and their potential to determine risk of re‐injury. Further, future rehabilitation can target specific intervention programmes to restore motor control.Highlights Motor unit strategies of arthrogenic muscle inhibition are characterised for the first time via decomposed EMG. Motor unit deficits of thigh musculature persist throughout all phases of ACL rehabilitation, even after return‐to‐sport. After ACL injury, motor unit sizes at similar recruitment thresholds were smaller than those of healthy controls.