Kazuki Takizawa

Motion-based design of elastic belts for passive assistive device using musculoskeletal model

We are developing a passive power assist supporter called Smart Suit Lite. Smart Suit Lite is a compact and lightweight power assist device that utilizes the elastic force of elastic belts. To design the Smart Suit Lite, we developed a motion-based assist method and an extended musculoskeletal model. The motion-based assist method was used to design the arrangements and properties of the elastic belts by utilizing the relation between the target motions and the corresponding muscle forces. To analyze the assistive forces provided by the elastic belts, skin segments that represent the surface of the human body features the extended musculoskeletal model and can reproduce changes in length of the body surface with changes in posture. In this study, we used the developed method to produce the Smart Suit Lite for care workers. Furthermore, through a trial experiment, we found that wear comfort was strongly correlated with the assistance perceived the user. Thus, we have improved the Smart Suit Lite from the aspect of wear comfort, and verified the enhancement of the assistance provided by the device. In user testing, 90% of the participants reported a decrease in load on the low back during care work.

Acute Effect of Dynamic Stretching on Endurance Running Performance in Well-Trained Male Runners.

Abstract Yamaguchi, T, Takizawa, K, and Shibata, K. Acute effect of dynamic stretching on endurance running performance in well-trained male runners. J Strength Cond Res 29(11): 3045–3052, 2015—The purpose of this study was to clarify the acute effect of dynamic stretching (DS) on relative high-intensity endurance running performance. The endurance running performances of 7 well-trained middle- or long-distance male runners were assessed on a treadmill after 2 types of pretreatment. The pretreatments were nonstretching (NS) and DS treatment. In the DS treatment, DS was performed as 1 set of 10 repetitions as quickly as possible for the 5 muscle groups in lower extremities. The endurance running performances were evaluated by time to exhaustion (TTE) and total running distance (TRD) during running at a velocity equivalent to 90% maximal oxygen uptake (VO2max) in each subject. The oxygen uptake (VO2) during running was measured as an index of running economy (RE). The TTE (928.6 ± 215.0 seconds) after DS treatment was significantly (p < 0.01) more prolonged compared with that (785.3 ± 206.2 seconds) after NS. The TRD (4,301.2 ± 893.8 m) after DS treatment was also significantly (p < 0.01) longer than that (3,616.9 ± 783.3 m) after NS. The changes in the VO2 during running, however, did not significantly (p > 0.05) differ between the pretreatments. The results demonstrated that the DS treatment improved the endurance performance of running at a velocity equivalent to 90% VO2max in well-trained male runners, although it did not change the RE. This running velocity is equivalent to that for a 3,000- or 5,000-m race. Our finding suggests that performing DS during warm-up before a race is effective for improving performance.

Effect of warm-up exercise on delayed-onset muscle soreness

Abstract In this study, we wished to determine whether a warm-up exercise consisting of 100 submaximal concentric contractions would attenuate delayed-onset muscle soreness and decreases in muscle strength associated with eccentric exercise-induced muscle damage. Ten male students performed two bouts of an elbow flexor exercise consisting of 12 maximal eccentric contractions with a warm-up exercise for one arm (warm-up) and without warm-up for the other arm (control) in a randomized, counterbalanced order separated by 4 weeks. Muscle temperature of the biceps brachii prior to the exercise was compared between the arms, and muscle activity of the biceps brachii during the exercise was assessed by surface integral electromyogram (iEMG). Changes in visual analogue scale for muscle soreness and maximal voluntary isometric contraction strength (MVC) of the elbow flexors were assessed before, immediately after, and every 24 h for 5 days following exercise, and compared between the warm-up and control conditions by a two-way repeated-measures analysis of variance. The pre-exercise biceps brachii muscle temperature was significantly (P<0.01) higher for the warm-up (35.8±0.2°C) than the control condition (34.4±0.2°C), but no significant differences in iEMG and torque produced during exercise were evident between conditions. Changes in muscle soreness and MVC were not significantly different between conditions, although these variables showed significant (P<0.05) changes over time. It was concluded that the warm-up exercise was not effective in mitigating delayed-onset muscle soreness and loss of muscle strength following maximal eccentric exercise.

Muscle damage and soreness following a 50-km cross-country ski race

Abstract In this study, we examined indirect markers of muscle damage and muscle soreness following a 50-km cross-country ski race completed in 2 h and 57 min to 5 h and 9 min by 11 moderately trained male university students. Maximal strength of the knee extensors, several blood markers of muscle damage and inflammation, and muscle soreness (visual analog scale: 0 = “no pain”, 50 mm = “unbearably painful”) were measured one day before, immediately after, and 24, 48, 72, and 144 h after the race. Changes in the measures over time were analysed using one-way repeated-measures analysis of variance and a Fishers post-hoc test. Maximal strength of the knee extensors decreased significantly (P<0.05) immediately after the race (mean −27%, s=6), but returned to pre-exercise values within 24 h of the race. All blood markers increased significantly (P<0.05) following the race, peaking either immediately (lactate dehydrogenase: 253.7 IU · l−1, s=13.3; myoglobin: 476.4 ng · ml−1, s=85.5) or 24 h after the race (creatine kinase: 848.0 IU · l−1, s=151.9; glumatic oxaloacetic transaminase: 44.3 IU · l−1, s=4.2; aldolase: 10.0 IU · l−1, s=1.3; C-reactive protein: 0.36 IU · l−1, s=0.08). Muscle soreness developed in the leg, arm, shoulder, back, and abdomen muscles immediately after the race (10–30 mm), but decreased after 24 h (<15 mm), and disappeared 48 h after the race. These results suggest that muscle damage induced by a 50-km cross-country ski race is mild and recovery from the race does not take long.

Warm-up exercises may not be so important for enhancing submaximal running performance

Abstract Takizawa, K, Yamaguchi, T, and Shibata, K. Warm-up exercises may not be so important for enhancing submaximal running performance. J Strength Cond Res 32(5): 1383–1390, 2018—The purpose of this study was to determine an appropriate warm-up intensity for enhancing performance in submaximal running at 90% vV[Combining Dot Above]O2max (it assumes 3,000–5,000 m in track events). Seven trained male university athletes took part in this study (age: 21.3 ± 2.1 years, height: 169.3 ± 4.7 cm, body mass: 58.4 ± 5.6 kg, V[Combining Dot Above]O2max: 73.33 ± 5.46 ml·kg−1·min−1). Each subject ran on a treadmill at 90% vV[Combining Dot Above]O2max until exhaustion after 1 of 4 warm-up treatments. The 4 warm-up treatments were no warm-up, 15 minutes running at 60% vV[Combining Dot Above]O2max, at 70% vV[Combining Dot Above]O2max, and at 80% vV[Combining Dot Above]O2max. The running performance was evaluated by time to exhaustion (TTE). V[Combining Dot Above]O2, and vastus lateralis muscle temperature were also measured. There were no significant differences in TTE among the warm-up exercises (p > 0.05). V[Combining Dot Above]O2 in no warm-up showed slower reaction than the other warm-up exercises. Regarding, the vastus lateralis muscle temperature immediately after warm-up, no warm-up was significantly (p < 0.01) lower compared with the other warm-up exercises. Our results suggested that submaximal running performance was not affected by the presence or absence of a warm-up or by warm-up intensity, although physiological changes occurred.

Postural stabilization by trunk tightening force generated by passive power-assist device

We are developing a passive power-assist supporter called Smart Suit Lite, which is a compact and lightweight power-assist device that utilizes the restoring force of elastic belts. Smart Suit Lite is designed not only to support muscles but also to stabilize the torso similarly to a corset. However, because a corset is always tight around the waist, negative effects caused by long-term use has been pointed out. In contrast, the tightening force generated by Smart Suit Lite increases only when the wearer adopts a posture corresponding to higher load on the low back. In this research, we performed two basic experiments to evaluate the static balance ability of wearers. As a result, the standard deviation of the lumbar angle decreased by 32.1% on average in wearers with low stability.

Effects of 3-Week Work-Matched High-Intensity Intermittent Cycling Training with Different Cadences on VO2max in University Athletes

The aim of this study is to clarify the effects of 3-week work-matched high-intensity intermittent cycling training (HIICT) with different cadences on the VO2max of university athletes. Eighteen university athletes performed HIICT with either 60 rpm (n = 9) or 120 rpm (n = 9). The HIICT consisted of eight sets of 20 s exercise with a 10 s passive rest between each set. The initial training intensity was set at 135% of VO2max and was decreased by 5% every two sets. Athletes in both groups performed nine sessions of HIICT during a 3-week period. The total workload and achievement rate of the workload calculated before experiments in each group were used for analysis. VO2max was measured pre- and post-training. After 3 weeks of training, no significant differences in the total workload and the achievement rate of the workload were found between the two groups. VO2max similarly increased in both groups from pre- to post-training (p = 0.016), with no significant differences between the groups (p = 0.680). These results suggest that cadence during HIICT is not a training variable affecting the effect of VO2max.

Field Testing of the Influence of Assistive Wear on the Physical Fitness of Nursing-Care Workers

There are several problems involved with introducing assistive technologies, which amplify human physical strength or reduce fatigue, to actual environment. One of the problem is that there is the possibility that the muscular strength of the user decline due to the reduction of the physical burden associated with the work. Therefore, the changes in physical performance due to the use of the assistive devices need to be quantitatively evaluated. In this study, a four-week monitoring test (including a two-week trial period) was performed with a total of 30 nursing-care workers in a nursing home. The participants wore an assistive wear “Smart Suit Lite” for two weeks and their subjective fatigue and physical strength were evaluated over the course of the study. The results show that the feeling of fatigue was decreased in each of the subjects by an average of 16% as a result of using the assistive wear. However, there was no significant difference in the subjects’ physical fitness (back-muscle strength, grip strength, sitting–standing capability, standing long-jump ability, or one-legged standing ability), indicating that there was no decrease in physical strength due to the use of the Smart Suit Lite during normal work over two weeks.