Mitsuhiko Masuhara

Effects of chronic treadmill running on neurogenesis in the dentate gyrus of the hippocampus of adult rat.

Proliferating astrocytes and proliferating neuroblasts have been observed in the subgranular zone (SGZ) of the dentate gyrus (DG) in the hippocampus of adult rats under normal conditions. However, whether these proliferating cells are stimulated by running has not been determined. Using immunohistochemical techniques, we examined the effects of chronic treadmill running on proliferating astrocytes (PCNA+/GFAP+ cells), proliferating neuroblasts (PCNA+/DCX+ cells) and newly generated postmitotic neurons (DCX+/NeuN+ cells) in the DG of the hippocampus of adult rats and also characterized the morphological features of PCNA+/GFAP+ cells and PCNA+/DCX+ cells. PCNA+/GFAP+ cells with few processes and PCNA+/DCX+ cells without long processes were detected in the SGZ, and we determined that these are morphological features of the astrocytes and neuroblasts with proliferative ability. Chronic treadmill running (at a speed of 22 m/min, 30 min/days for 7 days) significantly increased the numbers of PCNA+/GFAP+ cells and DCX+/NeuN+ cells, and the number of PCNA+/DCX+ cells tended to increase by chronic treadmill running. These results indicate that chronic treadmill running stimulates the proliferation of astrocytes in the SGZ. Furthermore, the present study indicates that chronic treadmill running increases DCX+/NeuN+ cells that are detected in a transient stage during the neuronal maturation process. These events may be the cellular basis mediating both running-induced increases of new neurons in the DG of the hippocampus and running-induced improvement of learning and memory functions of adult rats.

Acute effects of self-myofascial release using a foam roller on arterial function.

Abstract Okamoto, T, Masuhara, M, and Ikuta, K. Acute effects of self-myofascial release using a foam roller on arterial function. J Strength Cond Res 28(1): 69–73, 2014—Flexibility is associated with arterial distensibility. Many individuals involved in sport, exercise, and/or fitness perform self-myofascial release (SMR) using a foam roller, which restores muscles, tendons, ligaments, fascia, and/or soft-tissue extensibility. However, the effect of SMR on arterial stiffness and vascular endothelial function using a foam roller is unknown. This study investigates the acute effect of SMR using a foam roller on arterial stiffness and vascular endothelial function. Ten healthy young adults performed SMR and control (CON) trials on separate days in a randomized controlled crossover fashion. Brachial-ankle pulse wave velocity (baPWV), blood pressure, heart rate, and plasma nitric oxide (NO) concentration were measured before and 30 minutes after both SMR and CON trials. The participants performed SMR of the adductor, hamstrings, quadriceps, iliotibial band, and trapezius. Pressure was self-adjusted during myofascial release by applying body weight to the roller and using the hands and feet to offset weight as required. The roller was placed under the target tissue area, and the body was moved back and forth across the roller. In the CON trial, SMR was not performed. The baPWV significantly decreased (from 1,202 ± 105 to 1,074 ± 110 cm·s−1) and the plasma NO concentration significantly increased (from 20.4 ± 6.9 to 34.4 ± 17.2 &mgr;mol·L−1) after SMR using a foam roller (both p < 0.05), but neither significantly differed after CON trials. These results indicate that SMR using a foam roller reduces arterial stiffness and improves vascular endothelial function.

Cardiovascular responses induced during high-intensity eccentric and concentric isokinetic muscle contraction in healthy young adults.

The purpose of this study was to determine the differences in cardiovascular response between high‐intensity eccentric (ECC) and concentric (CON) contractions, and to obtain the basic data applicable to resistance training in middle‐aged and elderly individuals. The subjects who participated in this study were nine healthy men (age 24·1 ± 1·3 years). ECC and CON were randomly selected, as each test consisted of a high‐intensity (80% of peak torque) bout of 60 s of ECC and CON isokinetic contractions of the flexor carpi radialis. Systolic pressure (SBP), diastolic pressure (DBP) and heart rate (HR) during ECC and CON were measured using a Finometer. Mean arterial pressure (MAP) was calculated by SBP and DBP. Rate‐pressure product (RPP) was calculated by SBP and HR. SBP, DBP, MAP and RPP during ECC were significantly smaller compared with CON. It is clear that cardiovascular response by high‐intensity contraction is smaller in ECC than in CON. High‐intensity ECC has been suggested to exert only small stress to the cardiovascular system. Thus, being a contraction mode it may be applicable to resistance training.

Alterations of M-cadherin, neural cell adhesion molecule and β-catenin expression in satellite cells during overload-induced skeletal muscle hypertrophy

Aim:  Neural cell adhesion molecule (NCAM) and M‐cadherin are cell adhesion molecules expressed on the surface of skeletal muscle satellite cell (SC). During myogenic morphogenesis, M‐cadherin participates in mediating terminal differentiation and fusion of myoblasts by forming a complex with β‐catenin and that NCAM contributes to myotube formation by fusion of myoblasts. Hypertrophy and hyperplasia of functionally overloaded skeletal muscle results from the fusion with SCs into the existing myofibres or new myofibre formation by SC–SC fusion. However, the alterations of NCAM, M‐cadherin and β‐catenin expressions in SCs in response to functional overload have not been investigated.

Characteristics of locomotion, muscle strength, and muscle tissue in regenerating rat skeletal muscles

Although numerous studies have aimed to elucidate the mechanisms used to repair the structure and function of injured skeletal muscles, it remains unclear how and when movement recovers following damage. We performed a temporal analysis to characterize the changes in movement, muscle function, and muscle structure after muscle injury induced by the drop‐mass technique. At each time‐point, movement recovery was determined by ankle kinematic analysis of locomotion, and functional recovery was represented by isometric force. As a histological analysis, the cross‐sectional area of myotubes was measured to examine structural regeneration. The dorsiflexion angle of the ankle, as assessed by kinematic analysis of locomotion, increased after injury and then returned to control levels by day 14 post‐injury. The isometric force returned to normal levels by day 21 post‐injury. However, the size of the myotubes did not reach normal levels, even at day 21 post‐injury. These results indicate that recovery of locomotion occurs prior to recovery of isometric force and that functional recovery occurs earlier than structural regeneration. Thus, it is suggested that recovery of the movement and function of injured skeletal muscles might be insufficient as markers for estimating the degree of neuromuscular system reconstitution. Muscle Nerve 41: 694–701, 2010

The expression patterns of Pax7 in satellite cells during overload-induced rat adult skeletal muscle hypertrophy.

Aim:  Activated satellite cells (SCs) have the ability to reacquire a quiescent, undifferentiated state. Pax7 plays a crucial role in allowing activated SCs to undergo self‐renewal. Because the increase in the SC population is induced during overload‐induced skeletal muscle hypertrophy, it is possible that Pax7‐regulated SC self‐renewal is involved in the modulation of the SC population during the functional overload of skeletal muscles. However, the characteristics of the expression patterns of Pax7 in SCs during the functional overload of adult skeletal muscles are poorly understood.

Relationship between plasma endothelin-1 concentration and cardiovascular responses during high-intensity eccentric and concentric exercise.

The present study investigates the relationship between plasma endothelin‐1 (ET‐1) concentrations and cardiovascular responses during eccentric (ECC) and concentric (CON) resistance exercises. Eight healthy males (aged 24·3 ± 1·2 years) performed dynamic forearm exercises for 60 s at an angular velocity of 60º s−1. Each test comprised 60‐s high‐intensity (80% of peak torque) bouts of randomly selected ECC and CON contractions, and the plasma ET‐1 concentrations were measured before and after each type of contraction. Systolic pressure (SBP), diastolic pressure (DBP), pulse pressure and heart rate (HR) during ECC and CON contraction were also measured. Mean arterial pressure (MAP) was calculated from SBP and DBP. The rate‐pressure product (RPP) was calculated from SBP and HR. The plasma ET‐1 concentration was significantly increased after CON, compared with ECC contraction (P<0·01). Moreover, SBP, DBP, MAP and RPP were significantly increased (P<0·05, P<0·01, P<0·001, respectively) during CON, compared with ECC contraction. Correlations between plasma ET‐1 concentration and MAP were not significant during ECC contraction, but significantly positive during CON contraction (P<0·05). These results showed that CON contraction is associated with ET‐1 production and a greater increase in blood pressure compared with ECC contraction.

Low-intensity resistance exercise with slow lifting and lowering does not increase noradrenalin and cardiovascular responses

The aim of this study was to investigate the effect of low‐intensity resistance exercise with slow lifting and lowering (LSL) on plasma endothelin‐1 (ET‐1) and noradrenalin concentrations in young healthy adults. Eight healthy males participated in this study (age 19·0 ± 0·5 years, mean ± SD). The LSL performed the 10 repetitions with 3 s eccentric (lowering phase) and 3 s concentric (lifting phase) muscle actions. The high‐intensity resistance exercise with normal lifting and lowering (HNL) performed the 10 repetitions with 1 s eccentric (lowering phase) and 1 s concentric (lifting phase) muscle actions. The load was set to 40% of one repetition maximal (1RM) for LSL and 80% of 1RM for HNL. Plasma ET‐1 and noradrenalin concentrations were measured before and after each type of exercise. Systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), pulse pressure (PP) and heart rate (HR) during LSL and HNL were measured. The rate‐pressure product (RPP) was calculated from SBP and HR. There were no significant differences in the plasma ET‐1 concentration between LSL and HNL. However, the plasma noradrenalin concentration was significantly increased after HNL, compared with LSL (P<0·001). SBP, DBP, PP, MAP, HR and RPP during LSL were significantly lower compared with HNL (P<0·05: PP and HR; P<0·01: RPP; P<0·001: SBP, DBP and MAP). These results suggested that LSL may suppress the increase in plasma noradrenalin concentrations and cardiovascular responses.

Low-Intensity Resistance Training after High-Intensity Resistance Training can Prevent the Increase of Central Arterial Stiffness

Although high-intensity resistance training increases arterial stiffness, low-intensity resistance training reduces arterial stiffness. The present study investigates the effect of low-intensity resistance training before and after high-intensity resistance training on arterial stiffness. 30 young healthy subjects were randomly assigned to a group that performed low-intensity resistance training before high-intensity resistance training (BLRT, n=10), a group that performed low-intensity resistance training after high-intensity resistance training (ALRT, n=10) and a sedentary control group (n=10). The BLRT and ALRT groups performed resistance training at 80% and 50% of one repetition maximum twice each week for 10 wk. Arterial stiffness was measured using carotid-femoral and femoral-ankle pulse wave velocity (PWV). One-repetition maximum strength in the both ALRT and BLRT significantly increased after the intervention (P<0.05 to P<0.01). Both carotid-femoral PWV and femoral-ankle PWV after combined training in the ALRT group did not change from before training. In contrast, carotid-femoral PWV after combined training in the BLRT group increased from before training (P <0.05). Femoral-ankle PWV after combined training in the both BLRT and ALRT groups did not change from before training. These results suggest that although arterial stiffness is increased by low-intensity resistance training before high-intensity resistance training, performing low-intensity resistance training thereafter can prevent the increase of arterial stiffness.

Effects of rapid or slow body mass reduction on body composition in adult rats.

Whether the speed of body mass (BM) reduction influences the body composition is uncertain. To investigate the effects of rapid vs slow body mass reduction on body composition, rats were divided into three groups; fed ad libitum for 16-day (Control, C); received restricted food intake during 16-day to decrease BM slowly (Slow, S); or fed ad libitum for 13-days and fasted for the last 3 days to rapidly reach a BM comparable to that of S (Rapid, R). Drinking water was restricted for R on day 16 to rapidly decrease their BM. All rats trained during the study. Final BM and adipose tissues mass were similar for R and S, and both were lesser than C. The skeletal muscle mass did not decrease in R and S. The liver mass was lower in R and S than C, and the decrease tended to be greater in R than S. Both the stomach and small intestine masses were significantly lower in R than C, but did not differ between S and C. In conclusion, differences of the speed of BM reduction affect the splanchnic tissues, and the decrease in splanchnic tissue mass was greater with rapid than slow BM reduction.