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Muscular imbalance increases the risk of non-contact injuries among youth athletes. This study aimed to examine the isokinetic hamstring-to-quadriceps strength (H/Q) ratios between the dominant and non-dominant legs in youth taekwondo (TKD) players. Sixty-three youth TKD players voluntarily participated in this study. The isokinetic muscle strength test was performed at three different angular velocities (60°·s−1, 120°·s−1 and 240°·s−1) with concentric (Con) and eccentric (Ecc) contraction modes. The conventional (HCon/QCon) and functional (HEcc/QCon) H/Q strength ratios were determined. Hamstring muscle strength was significantly greater in the dominant leg than in the non-dominant leg at 60°·s−1 (Con contraction) and at 120°·s−1 and 240°·s−1 (Ecc contraction). Conventional and functional H/Q strength ratios were higher in the dominant leg than in the non-dominant leg at 240°·s−1, and the strength ratios increased with angular velocity. The asymmetry of conventional and functional H/Q strength ratios between the dominant and non-dominant legs may affect the risk of non-contact injuries among youth TKD players; thus, coaches should include specialized training programs to balance the H/Q strength ratios between legs. In particular, unilateral eccentric hamstring exercises for the nondominant leg are important for preventing noncontact injuries.

Abstract Purpose Physical activity (PA) is a modifiable factor in preventing/treating cardiometabolic disease. However, no studies have yet compared specific moderate-to-vigorous PA (MVPA) domains with the risk of metabolic syndrome (MetS) in detail. Here, the present study was conducted to examine the impact of different MVPA domains (leisure-time PA (LTPA) vs. occupational PA (OPA) vs. total MVPA) on the risk of MetS in Korean adults. Materials and methods: Data from the 2014 to 2021 Korea National Health and Nutrition Examination Survey were analyzed (N = 31,558). MetS was defined according to the criteria by revised NCEP/ATP-III. The domain-specific MVPA was assessed using the K-GPAQ. The LTPA and OPA status were classified into four categories: (1) 0 min/week, (2) 1 to 149 min/week, (3) 150 to 299 min/week, and 4) ≥ 300 min/week. In addition, the present study calculated total MVPA as a sum of OPA and LTPA and further classified it into six groups; (1) 0 min/week, (2) 1 to 149 min/week, (3) 150 to 299 min/week, (4) 300 to 449 min/week, (5) 450 to 599 min/week, 6) ≥ 600 min/week. Results: The ≥ 300 min/week and the 150 to 299 min/week of LTPA showed better outcomes in cardiometabolic disease risk factors and surrogate markers of insulin resistance compared with the 0 min/week of LTPA regardless of adiposity status. Risk of MetS in ≥ 300 min/week of LTPA was lower than in 0 min/week, 1 to 149 min/week, and 150 to 299. In addition, LTPA was significantly associated with a risk of the MetS in a curvilinear dose-response curve, however, no significant effects of a non-linear relationship between OPA and risk of the MetS. Conclusions: Our findings showed that LTPA was associated with a risk of MetS with a dose-response curve, whereas no significant non-linear effects were found between OPA and the risk of MetS. Therefore, the MVPA domain is an independent factor of the risk of MetS.

The purpose of this study was to compare different high-intensity interval training (HIIT) protocols with different lengths of work and rest times for a single session (all three had identical work-to-rest ratios and exercise intensities) for cardiac auto-regulation using a wearable device. With a randomized counter-balanced crossover, 13 physically active young male adults (age: 19.4 years, BMI: 21.9 kg/m2) were included. The HIIT included a warm-up of at least 5 min and three protocols of 10 s/50 s (20 sets), 20 s/100 s (10 sets), and 40 s/200 s (5 sets), with intensities ranging from 115 to 130% Wattmax. Cardiac auto-regulation was measured using a non-invasive method and a wearable device, including HRV and vascular function. Immediately after the HIIT session, the 40 s/200 s protocol produced the most intense stimulation in R-R interval (Δ-33.5%), ln low-frequency domain (Δ-42.6%), ln high-frequency domain (Δ-73.4%), and ln LF/HF ratio (Δ416.7%, all p < 0.05) compared to other protocols of 10 s/50 s and 20 s/100 s. The post-exercise hypotension in the bilateral ankle area was observed in the 40 s/200 s protocol only at 5 min after HIIT (right: Δ-12.2%, left: Δ-12.6%, all p < 0.05). This study confirmed that a longer work time might be more effective in stimulating cardiac auto-regulation using a wearable device, despite identical work-to-rest ratios and exercise intensity. Additional studies with 24 h measurements of cardiac autoregulation using wearable devices in response to various HIIT protocols are warranted.

PURPOSE This study aimed to examine the associations between accelerometer-measured physical activity and both cardiometabolic disease risk factors and metabolic syndrome in Korean adults. METHODS We performed a retrospective cohort study with age-sex matched case-control using data from the 2014-2016 Korea National Health and Nutrition Examination Survey, which was administered to South Korean adults (n=320). Individuals were categorized into quartiles based on accelerometer-measured moderate-to-vigorous physical activity (MVPA). Demographic and physical characteristics, waist circumference, visceral adiposity index, blood pressure, lipid profiles, and TG/HDL-C were observed. The associations between MVPA status and cardiometabolic disease risk factors as well as metabolic syndrome were determined using multiple logistic regression. RESULTS For the waist circumference, SBP, DBP, MBP, visceral adiposity, triglyceride, and a surrogate estimate of insulin resistance, the Q1 and Q2 groups had higher means compared with the Q3 and Q4 groups. HDL-C was higher in the Q3 and Q4 groups compared to the Q1 and Q2 groups. Odds ratios for cardiometabolic disease risk factors and metabolic syndrome decreased in a curvilinear manner with the increasing quartile of MVPA. CONCLUSIONS Adults with higher MVPA participation were strongly associated with cardiometabolic disease risk factors and metabolic syndrome.

ObjectivesAmong US firefighters, sudden cardiac arrest and psychological stress (i.e., PTSD) are the leading cause of on-duty death. Metabolic syndrome (MetSyn) may influence both cardiometabolic and cognitive health. Here, we examined differences in cardiometabolic disease risk factors, cognitive function, and physical fitness in US firefighters with vs. without MetSyn.Materials and methodsOne hundred fourteen male firefighters, aged 20 to 60 years, participated in the study. US firefighters with MetSyn vs. non-MetSyn were divided by AHA/NHLBI criteria. Of them, we performed a paired-match analysis with respect to the age and BMI of firefighters with (n = 18) vs. without MetSyn (n = 18). The cardiometabolic disease risk factors included blood pressure, fasting glucose, blood lipid profiles [HDL-C, triglyceride (TG)], and surrogate markers of insulin resistance [TG/HDL-C, TG glucose index (TyG)]. The cognitive test included a psychomotor vigilance task as a measure of reaction time and a delayed-match-to-sample task (DMS) as a measure of memory, using the computer-based Psychological Experiment Building Language Version 2.0 program. The differences between MetSyn and non-MetSyn groups in US firefighters were analyzed using an independent t-test adjusted for age and BMI. In addition, Spearman correlation and stepwise multiple regression were conducted.ResultsUS firefighters with MetSyn exhibited severe insulin resistance estimated by TG/HDL-C and TyG (Cohen’s d > 0.8, all p 0.8, all p

This study examined the effects of high-impact weight-bearing exercise on bone mineral density (BMD) and bone metabolic markers in middle-aged premenopausal women. Forty middle-aged premenopausal women were initially enrolled, but thirty-one participants (40.34 ± 3.69 years) completed in the study. The subjects were randomly divided into two groups including the high-impact weight-bearing exercise group (HWE, n = 14) and control group (CON, n = 17). The HWE group participated in the exercise for 50 min a day, three days per week for four months, while the CON group maintained their regular lifestyle. The HWE program included 10 different high-impact weight-bearing exercises such as jumping and running. BMD was measured using DXA (Hologic, QDR 4500W, Marlborough, MA, USA). The bone metabolic markers including serum 25-(OH) D, intact parathyroid hormone (PTH), osteoprotegerin (OPG), osteopontin (OPN), receptor activator of nuclear factor κB ligand (RANKL), osteocalcin (OC), C-terminal telopeptide of type 1 collagen (CTX), and calcium were analyzed. The results showed that the BMDs of femur, lumbar, and forearm did not significantly change during the intervention period in both the HWE and CON groups. A significant decrease in bone formation markers such as OC (F = 10.514, p = 0.003, ηp2 = 0.266) and an increase in bone resorption marker including CTX (F = 8.768, p = 0.006, ηp2 = 0.232) were found only in the CON group, while these values did not change in the HWE group. There was a significant increase in serum 25-(OH) D (F = 4.451, p = 0.044, ηp2 = 0.133) in the HWE group. Our findings suggest that four months of HWE is not sufficient to improve BMD and bone metabolic markers, but this impact exercise program may prevent the age-associated changes in bone turnover markers in middle-aged premenopausal women.

High-intensity interval training (HIIT) is superior to other training strategies in both male and female healthy individuals. Understanding sex-specific differences in cardiac auto-regulation may contribute to the optimal training strategies for HIIT. The present study aimed to identify sex differences in heart rate variability (HRV) and vascular function following HIIT in young adults. Twenty-four physically active young male and female adults (M: 12, F: 12, age: 19.5 yr, BMI: 22.1 kg·m-2) volunteered to participate in the study. Participants performed 10 bouts of HIIT including 20 s of high-intensity cycling at 115-130% Wmax followed by 100 s of recovery. The cardiac auto-regulations including HRV and vascular function were measured at five different time points. The R-R interval, rMSSD, and SDNN were recovered faster in males than in females after 15 min of HIIT. There were sex differences in the autonomic nervous system where ln LF and ln HF activities along with sympathovagal balance (ln LF/HF) were greater in females compared with males immediately and 15 min after HIIT. However, no significant differences in blood pressure and brachial-ankle pulse wave velocity were observed between male and female participants. Overall, HRV was more activated in females than in males following HIIT, but the acute response in vascular function was not different between sexes. In future studies, sexspecific adaptations of cardiac auto regulation following repeated HIIT may need to be performed. [ABSTRACT FROM AUTHOR]

The combat sports athletes developed great gains in both muscular function and fatigue resistance by utilizing high-intensity interval training (HIIT). However, it has not been investigated fully whether different work-to-rest ratios of HIIT show the effectiveness on muscle function in adolescent athletes. The purpose of the study was to compare different work-to-rest ratios by applying different rest times in response to the identical work time during HIIT on muscle function in adolescent taekwondo athletes. Forty-seven adolescent male taekwondo athletes (mean age: 16.7±0.8 years) were randomly assigned to the control group (n=11) vs. three HIIT groups by work-to-rest ratios; (1) 1:2 [30s:60s] (n=12), (2) 1:4 [30s:120s] (n=12), and (3) 1:8 [30s:240s] (n=12). All groups completed 10 experimental sessions over four weeks, while the control group maintained their regular taekwondo training. Muscular functions were measured by assessing isokinetic muscle strength and endurance of the knee extensor and flexor. The participants performed three sets of twenty maximal extension and flexion contractions at 120°s-1 with a 1-min interval between the sets for fatigue resistance. Blood samples were collected to measure free-testosterone, cortisol, creatine kinase, and urea as stress-torecovery indicators. A positive effect on improving muscle fatigue resistance was observed at the first set of assessments in the HIIT with 1:4 (Δ10.2%, p<.05) and 1:8 groups (Δ8.6%, p<.05). Additionally, the 1:4 group exhibited fatigue resistance improvement in the second set (Δ7.7%, p<.01) without any changes of stress-torecovery indicators, while the other groups did not show any improvement. The 30s all-out work with 120s rest time, lasting over a brief 4-week period, improved participants' fatigue resistance. A certain amount of rest time between high-intense movements is required to optimize muscle development in adolescent athletes compared with insufficient rest time. [ABSTRACT FROM AUTHOR]