Over the past few decades, several studies have been conducted on the relationships between peak blood lactate concentration (PBLC) and exercise performance. However, it is still controversial whether PBLC has a correlation with exercise performance, and if it can be a reliable indicator for energy metabolism during short-term high-intensity exercise. Thus, the purpose of the present study is to establish a new reliable indicator. PBLC isn’t able to reflect individual differences in kinetics of post-exercise blood lactate concentration (e.g. different time point of PBLC). Thus, to reflect the individual differences, we focused on the rate of increase in post-exercise blood lactate concentration (RIBLC). Twenty-two male university track athletes were divided into a sprinter group (S: n = 14) and middle- to long-distance runner group (ML: n = 8). 400-m (meter) time trials and blood samplings were conducted to measure exercise performance (average running velocity) and blood lactate concentration. In the present study, PBLC had no significant correlations with average running velocity in both S and ML. The present study supports previous studies that reported no correlations between PBLC and exercise performance. In contrast, significant correlations between RIBLC and average running velocity were observed in both S and ML (r = 0.69, p < 0.001 and r = 0.93, p < 0.01, respectively). RIBLC was significantly higher in ML than S (p < 0.05). It is assumed that RIBLC indicates lactate transport capacity and plays an important role in 400-m sprinting. Based on these results, RIBLC could be a new indicator for energy metabolism during short-term high-intensity exercise.
Eicosapentaenoic acid (EPA) is an omega-3 polyunsaturated fatty acid that is abundant in fish oil, and has anti-inflammatory or anti-obesity effects. However, the effects of EPA supplementation on mitochondrial content and dynamics (fusion and fission) in skeletal muscle has not been elucidated. We investigated the effects of EPA intake for 4 weeks on denervation-induced mitochondrial adaptation in mice skeletal muscle. ICR mice (male, 8 weeks old) were daily administrated olive oil (control) or EPA at a dose of 300 mg/kg body weight by gavage for 4 weeks. After 2 weeks of oil intake, mice underwent unilateral sciatic nerve transection surgery. The hindlimb without surgery served as the sham-operated control. Body and skeletal muscle weights did not differ between the control and the EPA groups. Peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1α) and oxidative phosphorylation (OXPHOS) proteins were significantly decreased by denervation surgery. Denervation also induced the reduction of mitochondrial fusion molecules and the increase of mitochondrial fission molecules. Expression levels of PGC-1α and mitochondrial respiration protein MTCO1 were higher in the EPA group than in the control (olive oil) group. In addition, the EPA group contained higher levels of mitochondrial fusion protein OPA1. Our results suggest that EPA intake prevents the reduction of mitochondrial content and fusion proteins in denervated skeletal muscle.
The objective of the present study was to examine the magnitude and timing of peak pelvis and thorax rotations in achieving high throwing velocities in pitching fastballs. During the preseason (Test 1 or T1) and four months later (Test 2 or T2), kinematic analysis was performed on eight elite youth pitchers throwing fastballs. Peak rotation velocities of the pelvis and thorax were determined and separation time, defined as the time between the maximal rotation velocities of the pelvis and thorax, was calculated. Peak thorax rotation velocity was not associated with throwing velocity. However, separation time appeared to be significantly and positively associated with throwing velocity. Also, the changes in separation time from T1 to T2 were significantly and positively associated with the observed increase in throwing velocity from T1 to T2. There was no significant association between the changes in pelvis or thorax peak rotation velocities from T1 to T2 and the change in throwing velocity. Results indicate that the relative timing of pelvis and thorax peak rotation velocity in pitching fastballs in baseball is likely to be a determinant of throwing velocity in skilled pitchers.
Although reconstruction from the 2011 Great East Japan earthquake and tsunami is proceeding, the environment of children living in the disaster area has not yet recovered. Anxiety among such children may have adverse effects on their future mental and physical health. The purpose of this study was to examine fluctuations in chronic stress and immune conditions in children and adolescents living in the disaster area. The participants were elementary and junior high school students living in the Pacific coastal area of northern Japan. This serial cross-sectional study performed five surveys in September 2011 (6 months, n = 391), March 2012 (1 year, n = 394), March 2013 (2 years, n = 281), March 2014 (3 years, n = 332), and March 2015 (4 years, n = 313). Stimulated whole saliva samples were collected, and saliva flow, secretory immunoglobulin A concentration, secretory immunoglobulin A secretion rate, and cortisol concentration were determined. Cortisol concentration significantly decreased from 6 months to year 2 of the study period, but increased between year 2 and year 4. Secretory immunoglobulin A concentration significantly increased between year 1 and year 4 compared to the first 6 months. Gender differences were observed in saliva flow and secretory immunoglobulin A concentration, and significant differences between elementary and junior high school students were observed in cortisol concentration. Therefore, fluctuation of cortisol concentration as a chronic stress biomarker and an increase in SIgA as an immune biomarker were observed during the 4 years after the disaster, but the changes in the two biomarkers did not correspond.
The purpose of the present study was to look at lower extremity force generation and neuromuscular activation by comparing isometric mid-thigh pull in the unilateral stance (IMTPUni) and bilateral stance (IMTPBi), and identifying the characteristics of IMTPUni. Fifteen male collegiate athletes (age: 20.60 ± 1.50 years, height: 1.74 ± 0.05 m, mass: 69.04 ± 4.23 kg) performed IMTPUni and IMTPBi as multi-joint isometric exercise. Ground reaction force (GRF) was measured to assess force generation during IMTP. Surface electromyography (EMG) was used to measure neuromuscular activation in the gluteus maximus (Gmax), gluteus medius (Gmed), semitendinosus, biceps femoris (BF), rectus femoris (RF) and vastus lateralis (VL), which were represented as average rectified values (ARVs). The EMG of the muscles during IMTPUni was normalized by IMTPBi to compare relative change among muscles. The co-contraction index (CI) during IMTPUni was also calculated by using normalized EMG. As a result, IMTPBi was significantly higher in BF than IMTPUni. However, in IMTPUni, although only one leg contributed to produce force, GRF of IMTPUni reached 80% of neuromuscular activity relative to IMTPBi. While the neuromuscular activation of Gmax, Gmed, BF, RF and VL was significantly higher proportionately in IMTPUni compared to IMTPBi, neuromuscular activation was even greater in Gmax and Gmed. The co-contraction index (CI) was increased in IMTPUni. The features of neuromuscular activation during IMTPUni were similar to the single leg squat and step-up exercise examined in previous studies due to the necessity to support the body with a single leg.
The aim of the present study was to report on the influence of food restriction on the bones of young female rats undergoing voluntary wheel running over 5 weeks. Seven-week-old female Sprague-Dawley rats were divided into three groups after a 1-week acclimatization period: a sedentary and ad libitum feeding group (SED), voluntary running exercise and ad libitum feeding group (EX), and voluntary running exercise and 30% food restriction group (EX-FR). The experiment lasted for 38 days. Results showed that the dry weight of the femur, length of the femur, bone mineral content (BMC) of the tibia, bone area of the tibia, bone mineral density (BMD) of the tibia, BMC of the lumbar, and bone area of the lumbar were significantly lower in the EX-FR group than in the SED and EX groups. BMD of the lumbar was not significantly different in each group. In conclusion, this study shows the possibility of constructing a rat model of a female athlete with low BMD in a short period of time.