Published papers

© 2019 Sports Medicine Australia Objectives: Muscle damage symptoms induced by unaccustomed eccentric contraction exercise can be reduced by repeating the experience several times. This phenomenon is termed the repeated bout effect. Although traditional biochemical markers require invasive blood sampling, biochemical measurements have recently been developed that can be non-invasively performed using urinary titin N-terminal fragment (UTF). However, it is unclear whether UTF can reflect the repeated bout effect. Therefore, the aim of the present study was to clarify whether UTF decreased with the repeated bout effect. Design: This study compared changes in muscle damage markers between bouts of exercise performed for the first and second time. Methods: Eight young men performed 30 eccentric exercises of the elbow flexor on the first day of the first week (Bout 1). A second bout of eccentric exercises, same as the first, was performed 2 weeks later, (Bout 2). The dependent variables were muscle soreness (SOR), maximal voluntary isometric contraction (MVIC), range of motion (ROM), creatine kinase (CK), and UTF. All dependent variables were analyzed using two-way analysis of variance. Results: No significant difference was observed in workload or peak torque between the first and second exercise bouts. SOR as well as CK and UTF were significantly lower and ROM and MVIC were significantly higher in Bout 2 in comparison to Bout 1. Conclusions: These results suggest that UTF sensitively reflects the repeated bout effect and exercise-induced muscle damage can be non-invasively measured.

© Journal of Sports Science and Medicine (2020). We aimed to compare the urinary titin N-terminal fragment (UTF) concentration after concentric and eccentric exercise and to clarify the specific response of UTF to exercise-induced muscle damage (EIMD). Nine healthy young men performed 30 concentric elbow flexion exercises with maximum effort, rested for at least eight weeks, and performed eccentric exercises at the same workload using the same arm. Changes in the maximal voluntary isometric contraction (MVIC), muscle soreness (SOR), range of motion (ROM), serum creatine kinase (CK) activity, and UTF concentrations were recorded before and after for six consecutive days after exercise. There was no significant difference in workload during exercise between the two exercise types. However, serum CK activity increased after eccentric exercise (p < 0.05). Additionally, MVIC, SOR, ROM, and UTF concentration were significantly higher after eccentric exercise than after concentric exercise (p < 0.05). Although workload was the same, the UTF concentration greatly increased after eccentric exercise. Based on these results, we suggest that UTF can be a non-invasive and highly specific biomarker of EIMD.

© 2020, The Author(s). This study investigated the relationship between push-in meter (PM) and ultrasound strain elastography (USE) for biceps brachii (BB) muscle hardness. BB hardness of 21 young men was assessed by PM and USE during rest and isometric contractions of six different intensities (15, 30, 45, 60, 75, 90% of maximal voluntary contraction: MVC) at 30°, 60° and 90° elbow flexion. Muscle hardness (E) was calculated from the force–displacement relationship in PM, and strain ratio (SR) between an acoustic coupler (elastic modulus: 22.6 kPa) and different regions of interest (ROIs) in BB was calculated and converted to Young’s modulus (YM) in USE. In resting muscle, E was 26.1 ± 6.4 kPa, and SR and YM for the whole BB was 0.88 ± 0.4 and 30.8 ± 12.8 kPa, respectively. A significant (p < 0.01) correlation was evident between E and logarithmical transformed SR (LTSR) for the ROI of whole BB (r = − 0.626), and E and converted YM (r = 0.615). E increased approximately ninefold from resting to 90% MVC, and E and LTSR (r = − 0.732 to − 0.880), and E and converted YM for the SR above 0.1 were correlated (r = 0.599–0.768, p < 0.01). These results suggest that muscle hardness values obtained by PM and USE are comparable.

Changes in biceps brachii muscle hardness assessed by a push-in meter (PM) and strain elastography (SE) were compared between eccentric (ECC) and concentric contractions (CON) of the elbow flexors to test the hypothesis that muscle hardness would increase greater after ECC. Ten men performed 5 sets of 10 ECC with their non-dominant arms and 5 sets of 10 CON with their dominant arms using a dumbbell corresponding to 50% of maximum voluntary isometric contraction (MVIC) force at 90º elbow flexion. Before and 1–4 days after the exercise, MVIC force, elbow joint angles, upper-arm circumference, and muscle soreness as muscle damage makers, and biceps brachii muscle hardness at maximally extended elbow joint by PM and SE were measured. Changes in these measures over time were compared between ECC and CON. All muscle damage markers showed greater changes after ECC than CON (p < 0.001). Muscle hardness assessed by PM and SE increased (p < 0.05) and peaked at 4 days post-ECC with 154.4 ± 90.0% (PM) and 156.2 ± 64.2% (SE) increases from the baseline, but did not change significantly after CON. The changes in muscle hardness post-ECC were correlated between PM and SE (r = 0.752, p < 0.001). A correlation (p < 0.001) between the normalized changes in resting elbow joint angle and changes in muscle hardness assessed by PM (r = − 0.772) or SE (r = − 0.745) was also found. These results supported the hypothesis and suggest that the increases in muscle hardness after ECC were associated with muscle damage (increased muscle stiffness), and PM and SE detected muscle hardness changes similarly.

This study aimed to investigate the relationship between the muscle shear modulus of the biceps brachii, urinary titin N-terminal fragment (UTF), and other damage markers after eccentric exercise. Seventeen healthy males performed five sets of ten eccentric exercises with dumbbells weighing 50% of the maximum voluntary contraction (MVC) at the elbow joint. Muscle shear modulus with range of interest set to only biceps brachii muscle measured by ultrasound shear wave elastography, UTF, MVC, range of motion (ROM), and soreness (SOR) were recorded before, immediately after, and 1, 24, 48, 72, 96, and 168 h after eccentric exercise. Each marker changed in a time course pattern, as found in previous studies. The peak shear modulus showed a moderate negative correlation with peak MVC (r = -0.531, P < 0.05) and a strong positive correlation with peak UTF (r = 0.707, P < 0.01). Our study results revealed a significant relationship between muscle strength, shear modulus measured by ultrasound SWE, and titin measured by UTF, as a non-invasive damage marker after eccentric exercise to track changes in EIMD.

Exercise is an effective strategy to prevent and improve obesity and related metabolic diseases. Exercise increases the metabolic demand in the body. Although many of the metabolic health benefits of exercise depend on skeletal muscle adaptations, exercise exerts many of its metabolic effects through the liver, adipose tissue, and pancreas. Therefore, exercise is the physiological state in which inter-organ signaling is most important. By contrast, circadian rhythms in mammals are associated with the regulation of several physiological and biological functions, including body temperature, sleep-wake cycle, physical activity, hormone secretion, and metabolism, which are controlled by clock genes. Glucose and lipid tolerance reportedly exhibit diurnal variations, being lower in the evening than in the morning. Therefore, the effects of exercise on substrate metabolism at different times of the day may differ. In this review, the importance of exercise timing considerations will be outlined, incorporating a chrono-exercise perspective.

Introduction: The fencing lunge (lunge), characterized by minimal body rotation, offers a movement well-suited for 2D video analysis. However, to the best of our knowledge, the validity of 2D video analysis for fencing has not been verified. This study aimed to validate 2D video analysis by comparing lower limb joints (hip, knee, and ankle joints) angles during lunge using both 2D video analysis and 3D motion analysis methods. Methods: Twenty-two male fencers performed lunge trials that were simultaneously recorded using eight motion capture cameras (Qualisys Miqus M1) and two digital video cameras (Sony AX-450 and AX450a). Results: The 2D video analysis results exhibited an extremely large correlation in knee joint angles of the front and rear legs in the sagittal with those from 3D motion analysis (r = 0.93–0.99). However, while a robust correlation was found between the ankle joint angles of the front and rear legs (r = 0.82–0.84), a large bias was also observed (−5.23° to −21.31°). Conversely, for the hip joints of the rear leg, a moderate correlation (r = 0.31) and a large bias (−10.89°) were identified. Conclusions: The results of this study will contribute to the development of coaching using 2D video analysis in competition settings because such analysis can be a useful alternative to 3D motion analysis when measuring the knee joint angle of the front leg and rear leg in the sagittal plane. However, for the ankle joint angle, further research on the optimal shooting position and height of the digital video camera is needed, whereas for the hip joint angle, 3D motion analysis is recommended at this time.

A noninvasive, immediate, and convenient method for assessing muscle tissue status during exercise-induced muscle damage (EIMD) has not been established. This study was designed to assess and determine parameters suitable for measuring EIMD after eccentric exercise, using multi-frequency bioimpedance analysis (BIA). Thirty-five young male participants performed dumbbell exercises with their left arm, and their BIA parameters were measured at various time points up to 168 h post exercise using a multi-frequency BIA device. At all-time points, intra and extracellular water content was greater in the left arm than in the right arm, whereas the impedance, reactance, resistance, and phase angle were lower in the left arm than in the right arm. Established EIMD indices, such as maximal isometric voluntary contraction, were measured and used in correlational analyses. Only reactance was correlated with biomarkers, indicating muscle damage (r =  - 0.56 to - 0.49). Furthermore, reactance was found to correlate well with indirect indicators of EIMD, suggesting that it may be a suitable marker for evaluating EIMD. However, the relationship with the limited evaluation indices employed in this study is constrained. Future studies should investigate the correlation between reactance and direct damage indicators, such as structural damage, observed in biopsies.

The stiffness of the triceps surae (TS) muscles during passive stretch has been increasingly studied using shear wave elastography (SWE). However, the continuous behavior of the Achilles tendon (AT) and its interaction with the TS muscles remain poorly understood, limiting understanding of tissue mechanics. This study aimed to characterize the angle-specific stiffness profiles of the individual TS muscles—the medial gastrocnemius (MG), lateral gastrocnemius (LG), and soleus (SOL)—and the AT during passive ankle dorsiflexion under identical experimental conditions. In this cross-sectional study, the ankles of 24 healthy university track and field athletes (age, 20.2 ± 1.3 years) were passively moved by a dynamometer from 30° of plantar flexion (PF) to 80% of maximum dorsiflexion (DF) at 1°/s (up to 25° DF). Shear wave velocity (SWV), an index of tissue stiffness, was measured at four sites (MG, LG, SOL, and AT). The percentage change in SWV from the −30° baseline was analyzed at 5° increments up to the neutral (0°) position using two-way analysis of variance. Significant SWV increases from baseline were observed at 10° PF for the MG, 5° PF for the LG, and 25° PF for the SOL. In contrast, the AT showed significant increases from 25° PF onward, with a rate of change consistently greater than that of all TS muscles across all measured angles. These findings indicate that the AT and TS exhibit asynchronous stiffening patterns: the tendon provides immediate resistance from the earliest range of motion, while the muscles remain compliant until further stretched. Thus, the tendon, rather than the muscle, primarily governs the initial resistive behavior of the muscle–tendon unit during passive stretch. Understanding this angle-specific behavior is essential for optimizing load management in rehabilitation and injury prevention.

Purpose: Bodyweight eccentric exercise training (ET), in which eccentric contractions are prolonged while minimizing the effort for concentric contractions, is shown to improve the physical functions of older adults. No previous study has compared this with bodyweight resistance exercise training in which both concentric and eccentric contractions are performed slowly (CET). We hypothesized that CET would produce better health and fitness outcomes than ET. Methods: Healthy older adults (65–89 years) were placed into the ET (n = 21) or CET group (n = 19). Both groups performed several bodyweight resistance exercises at a community center once and at home more than twice a week for 10 weeks. In the exercises, each eccentric contraction was 3 s for both groups, but each concentric contraction was performed with as little effort as possible for ET, but 3 s for CET. Resting heart rate, blood pressure, knee extensor muscle thickness (MT), maximal voluntary contraction strength (MVC), physical function tests (30-s chair stand: CS, 3-m timed up and go: TUG, sit and reach, 6-m walking time: 6WT and static balance) were assessed before and after the 10-week training, and their changes were compared between groups. Results: The subjective exercise intensity was lower (P < 0.01) for ET (2.2 ± 1.8/10) than CET (3.2 ± 1.7). Greater improvements in resting heart rate, blood pressure, CS, TUG, and 6WT were found for ET than CET, but MT and MVC increased similarly for both groups (P < 0.05). Conclusion: These results did not support the hypothesis in the present study design and showed that eccentric-focused training yielded greater benefits than slow concentric–eccentric training.

Purpose – This study aimed to determine whether runners with mid-portion Achilles tendinopathy (Achilles tendinopathy runners [ATR]) show altered ankle-angle-dependent mechanical behavior of the Achilles tendon and triceps surae muscle–tendon unit during passive dorsiflexion. Methods – Twelve ATR and 11 control runners (CON) participated in this study (ATR: age 43.9 ± 12.0 years, running distance 38.3 ± 22.3 km/week; CON: age 41.2 ± 13.7 years, running distance 48.2 ± 29.7 km/week). The participants underwent device-controlled passive ankle dorsiflexion (DF) from 30° of plantar flexion (PF) to 80% of maximal DF at 1°/s in the prone position with the knee extended. Shear wave velocity (SWV) (m/s) was measured in the medial gastrocnemius (MG), lateral gastrocnemius (LG), soleus (SOL), and Achilles tendon (AT). The primary analysis used repeated-measures analysis of variance with angle (30/25/20/15/10/5/0° PF) and region (MG/LG/SOL/AT) as within-subject factors and group as the between-subject factor. A secondary triceps surae-only model (MG/LG/SOL) included 5/10/15° DF because the AT could not be measured beyond neutral. Results – In the primary model, the region × angle × group interaction was significant, and AT SWV was lower in ATR than in CON at 10° PF (ATR: 6.97 ± 0.49 vs. CON: 8.70 ± 0.51 m/s), 5° PF (ATR: 7.97 ± 0.43 vs. CON: 9.31 ± 0.45 m/s), and 0° PF (ATR: 9.15 ± 0.57 vs. CON: 11.30 ± 0.60 m/s) (all p < 0.05). The MG and SOL SWV were lower in ATR at all PF angles, whereas the LG showed no differences. In the secondary model, the MG and SOL remained lower in ATR across 5–15° DF. Conclusion – The ATR group showed lower Achilles tendon SWV near neutral and consistently lower MG and SOL SWV across ankle angles. These findings suggest altered ankle-angle-dependent mechanical behavior of the Achilles tendon and MG–SOL components of the muscle–tendon unit in runners with Achilles tendinopathy.

© 2018 IOP Publishing Ltd. Objective: Muscle hardness measured by a push-in meter is calculated from a force-displacement curve (FDC) based on a two-layer spring model. Since a FDC is not linear, how to set a linear range in the FDC largely affects muscle hardness calculation. The present study investigated the linearity of the FDC to find the best portion relative to muscle thickness (MT) for muscle hardness measurement based on a two-layer spring model. Approach: Forty-seven men (age: 28 ±10 years, height: 176 ±7 cm, body mass: 73 ±11 kg) participated in the present study. Hardness of the biceps brachii muscle was measured at the mid-belly using a push-in meter. The FDC was obtained every 5% up to 50% of the MT, and linear regression equations of ten different portions within the FDC were calculated. The coefficient of determination (R 2 ) of each regression line was compared by ANOVA, and a piecewise linear regression analysis was performed by dividing the identified FDC into three linear segments. Results: One-way ANOVA showed a significant (p < 0.01) main effect in R 2 values of ten regression equations. Post-hoc analyses showed no significant differences in R 2 between 0%-15% MT and 0%-40% MT. While the linearity of the FDC was high between 0%-15% and 0%-40% MT, the highest R 2 value was found at 0%-25% and 0%-30% MT. According to the analysis of three linear segments in the FDC, the mean value of the point between the second and third segments was 28.5 ±4.3% MT. Significance: These results suggested that muscle hardness assessment using a push-in meter should be performed close to 30% MT depth for biceps brachii muscle.