Biomechanical study comparing the energy cost of human bipedalism versus zenkutsu-dachi stepping of a karateka.

Traditional stepping in the zenkutsu-dachi stance of the Shotokan style of karate is very physically demanding. It requires considerably more effort than what is expended during conventional human bipedalism. We performed a biomechanical study to analyze and compare these two types of gaits when performed by a highly experienced karateka. The study involved a three-dimensional motion analysis system (digital cameras and optical reflectors) and a force platform to analyze the ground reaction forces in all three planes. The study had both kinematic and kinetic components. We found that zenkutsu-dachi stepping is much more costly from an energetics point of view because the properties of the biarticular muscles are not used, the muscular moments of force are higher, and the body's potential energy is not converted into kinetic energy, contrary to the more economical model of human bipedalism that involves an inverted pendulum pattern.

Ankle Muscle Activations during Different Foot-Strike Patterns in Running.

This study analysed the landing performance and muscle activity of athletes in forefoot strike (FFS) and rearfoot strike (RFS) patterns. Ten male college participants were asked to perform two foot strikes patterns, each at a running speed of 6 km/h. Three inertial sensors and five EMG sensors as well as one 24 G accelerometer were synchronised to acquire joint kinematics parameters as well as muscle activation, respectively. In both the FFS and RFS patterns, according to the intraclass correlation coefficient, excellent reliability was found for landing performance and muscle activation. Paired t tests indicated significantly higher ankle plantar flexion in the FFS pattern. Moreover, biceps femoris (BF) and gastrocnemius medialis (GM) activation increased in the pre-stance phase of the FFS compared with that of RFS. The FFS pattern had significantly decreased tibialis anterior (TA) muscle activity compared with the RFS pattern during the pre-stance phase. The results demonstrated that the ankle strategy focused on controlling the foot strike pattern. The influence of the FFS pattern on muscle activity likely indicates that an athlete can increase both BF and GM muscles activity. Altered landing strategy in cases of FFS pattern may contribute both to the running efficiency and muscle activation of the lower extremity. Therefore, neuromuscular training and education are required to enable activation in dynamic running tasks.

Different changes of muscle hardness between the rectus femoris and vastus intermedius muscle after maximal knee extension exercise / 体力科学

This study aimed to determine the different changes of muscle hardness between the human rectus femoris (RF) and vastus intermedius muscle (VI) after maximal knee extension exercise. Eight healthy men (23.0±2.6 years) performed maximal isometric contraction (IM), concentric contraction (CC), and eccentric contraction (EC) exercises of the knee extensors. Muscle hardness (i.e., strain ratio, SR) and thickness in the proximal, middle, and distal parts of RF and VI were measured by using strain elastography before and after exercises. The rates of change between the values were calculated as values before exercise 100%. For VI, a significant main effect in “part” was found in IM and EC exercises in SR. Results show that SR in the distal part (IM, 89.0±27.2%; EC, 78.2±26.9%) was significantly lower than that in the middle part (IM, 105.5±34.3%; EC, 91.8±30.4%) for each exercise (p<0.05). However, no significant main effect in “part” was found in SR of RF in any exercise. A significant main effect was found in “part” in muscle thickness of RF in the IM exercise. Also, muscle thickness in the distal part (104.5±7.7%) was significantly higher than that in the proximal part (102.5±4.3%) for each exercise (p<0.05). These results suggest that changes of muscle hardness and thickness in the proximal, middle, and distal parts of the human rectus femoris and vastus intermedius muscle after maximal knee extension exercises are different.

The effect of accounting for biarticularity in hip flexor and hip extensor joint torque representations.

Subject-specific torque-driven models have ignored biarticular effects at the hip. The aim of this study was to establish the contribution of monoarticular hip flexors and hip extensors to total hip flexor and total hip extensor joint torques for an individual and to investigate whether torque-driven simulation models should consider incorporating biarticular effects at the hip joint. Maximum voluntary isometric and isovelocity hip flexion and hip extension joint torques were measured for a single participant together with surface electromyography. Single-joint and two-joint representations were fitted to the collected torque data and used to determine the maximum voluntary joint torque capacity. When comparing two-joint and single-joint representations, the single-joint representation had the capacity to produce larger maximum voluntary hip flexion torque (larger by around 9% of maximum torque) and smaller maximum voluntary hip extension torque (smaller by around 33% of maximum torque) with the knee extended. Considering the range of kinematics found for jumping movements, the single-joint hip flexors had the capacity to produce around 10% additional torque, while the single joint hip extensors had about 70% of the capacity of the two-joint representation. Two-joint representations may overcome an over-simplification of single-joint representations by accounting for biarticular effects, while building on the strength of determining subject-specific parameters from measurements on the participant.

Effect of hip joint angle on concentric knee extension torque.

This study tested the hypothesis that the effect of hip joint angle on concentric knee extension torque depends on knee joint angle during a single knee extension task. Twelve men performed concentric knee extensions in fully extended and 80° flexed hip positions with maximal effort. The angular velocities were set at 30°â€¯s-1 and 180°â€¯s-1. The peak torque and torques attained at 30°, 50°, 70° and 90° (anatomical position = 0°) of the knee joint were compared between the two hip positions. Muscle activations of the vastus lateralis, medialis, rectus femoris and biceps femoris were determined using surface electromyography. The peak torque was significantly greater in the flexed than in the extended hip position irrespective of angular velocity. The torques at 70° and 90° of the knee joint at both angular velocities and at 50° at 180°â€¯s-1 were significantly greater in the flexed than in the extended hip position, whereas corresponding differences were not found at 30° (at either angular velocity) and 50° (at 30°â€¯s-1) of the knee joint. No effect of hip position on muscle activation was observed in any muscle. These results supported our hypothesis and may be related to the force-length and force-velocity characteristics of the rectus femoris.

Unique activation of the quadriceps femoris during single- and multi-joint exercises.

PURPOSE: This study aimed to examine whether muscle activation of the quadriceps femoris differs between single- and multi-joint exercises, and to explore the factors resulting in muscle and exercise specificity in activation. METHODS: Eleven adults developed isometric hip extension torque gradually while maintaining submaximal isometric knee extension torque (Experiment 1). In Experiment 2, 15 men performed knee extension and leg press separately at intensities of 20, 40, 60 and 80 % of their one repetition maximum (1RM) load, and 14 men conducted leg press at intensities of 40 and 80 % of 1RM until exhaustion (Experiment 3). Muscle activation during exercises was measured using surface electromyography from the rectus femoris, vastus lateralis and medialis. RESULTS: The addition of isometric hip extension torque significantly decreased rectus femoris activation (Experiment 1). In Experiment 2, the rectus femoris activation was significantly higher during knee extension than during leg press, whereas no differences were observed in the vasti. The rectus femoris activation was not significantly different between leg press at 80 % and knee extension at 20 % of 1RM. The results of Experiment 3 showed significant increases in vasti activation at both intensities, whereas rectus femoris activation did not change at 80 % of 1RM. CONCLUSION: The results revealed that even at high intensity, the rectus femoris activation during multi-joint exercise is low and does not increase with fatigue, unlike the vasti, and that the inter-muscle and inter-exercise differences in activation depend on whether hip extension torque is exerted in the exercise.

Unique muscularity in cyclists' thigh and trunk: A cross-sectional and longitudinal study.

This study examined the influence of regular training in competitive cycling on individual muscle volume of the thigh and psoas major cross-sectionally and longitudinally. T1-weighted magnetic resonance (MR) images of the trunk and right thigh were obtained from eight experienced varsity male cyclists (experience: > 4 years) and 10 untrained men (experiment 1), and from 12 (10 males, two females) varsity cyclists before and after competitive cycling training for 6 months (experiment 2). From the MR images, the volumes of each of the quadriceps femoris and hamstrings, total adductors, gracilis, sartorius, and psoas major were determined. The volumes of the monoarticular thigh muscles, semitendinosus, and psoas major muscles were significantly greater in the experienced cyclists than in the untrained men (experiment 1), and increased significantly after the competitive training for 6 months (experiment 2). In contrast, the volumes of the other biarticular thigh muscles were similar among the experienced cyclists and untrained men (experiment 1), and did not change by competitive cycling training (experiment 2). The results indicate that competitive cycling training induces muscle-specific hypertrophy of the synergistic muscles, especially between the monoarticular and biarticular muscles, leading to quantitative profiles of the musculature in experienced cyclists.

Effects of gastrocnemius tightness on forefoot during gait.

The gastrocnemius is the main muscle of the posterior compartment of the leg. As a biarticular muscle it has specific biomechanical propertiess. This article discusses these properties combining the major biomechanical topics of anatomy, dynamics, kinetics, and electromyography. This muscle is remarkable in that it has very low energy consumption and very high mechanical efficacy. In addition to the biomechanical features, the consequences of its tightness are discussed. The dysfunction also appears in all the biomechanical topics and clarifies the reasons of the location of symptoms in the midfoot and on the plantar aspect of the forefoot.

Empirical evaluation of gastrocnemius and soleus function during walking.

Distinguishing gastrocnemius and soleus muscle function is relevant for treating gait disorders in which abnormal plantarflexor activity may contribute to pathological movement patterns. Our objective was to use experimental and computational analysis to determine the influence of gastrocnemius and soleus activity on lower limb movement, and determine if anatomical variability of the gastrocnemius affected its function. Our hypothesis was that these muscles exhibit distinct functions, with the gastrocnemius inducing limb flexion and the soleus inducing limb extension. To test this hypothesis, the gastrocnemius or soleus of 20 healthy participants was electrically stimulated for brief periods (90 ms) during mid- or terminal stance of a random gait cycle. Muscle function was characterized by the induced change in sagittal pelvis, hip, knee, and ankle angles occurring during the 200 ms after stimulation onset. Results were corroborated with computational forward dynamic gait models, by perturbing gastrocnemius or soleus activity during similar portions of the gait cycle. Mid- and terminal stance gastrocnemius stimulation induced posterior pelvic tilt, hip flexion and knee flexion. Mid-stance gastrocnemius stimulation also induced ankle dorsiflexion. In contrast mid-stance soleus stimulation induced anterior pelvic tilt, knee extension and plantarflexion, while late-stance soleus stimulation induced relatively little change in motion. Model predictions of induced hip, knee, and ankle motion were generally in the same direction as those of the experiments, though the gastrocnemius's results were shown to be quite sensitive to its knee-to-ankle moment arm ratio.

Gastrocnemius and soleus are selectively activated when adding knee extensor activity to plantar flexion.

The gastrocnemius is a biarticular muscle that acts not only as a plantar flexor, but also as a knee flexor, meaning that it is an antagonist during knee extension. In contrast, the soleus is a monoarticular plantar flexor. Based on this anatomical difference, these muscles' activities should be selectively activated during simultaneous plantar flexion and knee extension, which occur during many activities of daily living. This study examined the selective activation of gastrocnemius and soleus activities when voluntary isometric activation of knee extensors was added to voluntary isometric plantar flexion. Ten male volunteers performed isometric plantar flexion at 10%, 20%, and 30% of maximum effort. During each plantar flexion task, isometric knee extension was added at 0%, 50%, and 100% of maximum effort. When knee extension was added, the average rectified value of the electromyographic activity of the medial gastrocnemius was significantly depressed (P=.002), whereas that of the soleus was significantly increased (P<.001) regardless of the plantar flexion level. These results suggest that plantar flexion with concurrent knee extensor activity leads to selective activation of the soleus and depression of the synergistic activity of the gastrocnemius.

Effect of pre-fatigue method by leg extension exercise on recruitment state of synergists in thigh muscles during leg press exercise / 体力科学

The purpose of this study was to examine the recruitment state of synergistic muscles in the thigh muscles in leg press exercise with and without pre-fatigue method using transverse relaxation time (T2) on muscle functional magnetic resonance imaging (MRI). Nine healthy male subjects performed the following two types of exercise trials on separate days: 1) 5 sets of a leg press exercise with pre-fatigue method, which consisted of 3 sets of knee extension exercise (LP-pre), 2) 5 sets of a leg press exercise without pre-fatigue method (LP). Both exercises were performed at a load of 80% one-repetition maximum. Before and immediately after exercise, T2-weighted MR images of right-thigh were taken to calculate T2 values of twelve-thigh muscles. The T2 values for quadriceps femoris muscle and hamstrings in LP increased significantly after the exercise, except in the adductor magnus, adductor longus, gracilis, and sartorius. In contrast, the T2 values for all of the twelve-thigh muscles in LP-pre increased significantly after the exercise. Upon comparison between the two trials, the percentage changes in T2 value for the adductor magnus, adductor longus, and sartorius in LP-pre were found to be significantly greater than those in LP. These results suggest leg press exercise with pre-fatigue method may be effective to increase activity of synergistic muscles in thigh muscles during exercise.