Leg Action Research Articles

Human hopping on very soft elastic surfaces: implications for muscle pre-stretch and elastic energy storage in locomotion

During hopping in place and running, humans maintain similar center of mass dynamics by precisely adjusting leg mechanics to compensate for moderate changes in surface stiffness. We investigated the limits of this precise control by asking humans to hop in place on extremely soft elastic surfaces. We found that hoppers drastically altered leg mechanics and maintained similar center of mass dynamics despite a sevenfold change in surface stiffness (11-81 kN m(-1)). On the stiffest surfaces, the legs compressed in early stance and then extended in late stance in the pattern that is typical for normal bouncing gaits. On the softest surfaces, however, subjects reversed this pattern so that the legs extended up to 8 cm in early stance and then compressed by a similar distance in late stance. Consequently, the center of mass moved downward during stance by 5-7 cm less than the surface compressed and by a similar distance as on the stiffest surfaces. This unique leg action probably reduced extensor muscle pre-stretch because the joints first extended and then flexed during stance. This interpretation is supported by the observation that hoppers increased muscle activation by 50% on the softest surface despite similar joint moments and mechanical leg work as on the stiffest surface. Thus, the extreme adjustment to leg mechanics for very soft surfaces helps maintain normal center of mass dynamics but requires high muscle activation levels due to the loss of the normal extensor muscle stretch-shorten cycle.

Arm-Leg Coordination in Flat Breaststroke: A Comparative Study Between Elite and Non-Elite Swimmers

The aim of this study was to compare the arm-leg coordination in flat breaststroke among four groups of swimmers (elite males, elite females and non-elite males, non-elite females) of two different competitive levels. Using a velocity-video system, both forward acceleration and deceleration phases of the hip were first identified. Based on these phases, four temporal gaps indicated the time duration between arm and leg actions throughout three race paces (200, 100, and 50 m). For both groups, a velocity increase was combined with an increase of stroke rate, a decrease of stroke length, and an increase of the propulsive phases and a decrease of the glide phases. However, when the relative duration of one stroke cycle was considered, the elite swimmers had significant shorter time of the glide phase than lower competitive level swimmers (18.80 % vs. 31.04 % for females and 11.89 % vs. 19.60 % for males) combined with a longer stroke length (respectively 2.05 m vs. 1.73 m and 2.03 m vs. 1.82 m). Furthermore, the temporal gaps of the elite swimmers showed a greater continuity in the arm and leg actions, which indicates a better timing than non-elite swimmers. It was concluded that elite breaststroke swimmers are able to optimise their propulsion by reducing their glide phase and using a more continuous timing between arm and leg coordination.

Functional links between motor and language systems

Transcranial magnetic stimulation (TMS) was applied to motor areas in the left language-dominant hemisphere while right-handed human subjects made lexical decisions on words related to actions. Response times to words referring to leg actions (e.g. kick) were compared with those to words referring to movements involving the arms and hands (e.g. pick). TMS of hand and leg areas influenced the processing of arm and leg words differentially, as documented by a significant interaction of the factors Stimulation site and Word category. Arm area TMS led to faster arm than leg word responses and the reverse effect, faster lexical decisions on leg than arm words, was present when TMS was applied to leg areas. TMS-related differences between word categories were not seen in control conditions, when TMS was applied to hand and leg areas in the right hemisphere and during sham stimulation. Our results show that the left hemispheric cortical systems for language and action are linked to each other in a category-specific manner and that activation in motor and premotor areas can influence the processing of specific kinds of words semantically related to arm or leg actions. By demonstrating specific functional links between action and language systems during lexical processing, these results call into question modular theories of language and motor functions and provide evidence that the two systems interact in the processing of meaningful information about language and action.

Enhanced Human–Machine Interface in Braking

Antilock brake system (ABS) technology with powerful electronic components has shown superior braking performance to conventional vehicles on test tracks. On real highways, however, the performance of the ABS-equipped car has been disappointing. The poor braking performance with ABS has resulted from the questionable design of the human-machine interface for the brake system. The goal of this study is to design brake systems that provide more intuitive brake control and proper braking-performance information for the driver. In this study automotive brake systems are modeled as a type of master-slave telemanipulator. Human force-displacement interaction at the brake pedal has a strong effect on braking performance. As a preliminary study in brake-system design, the characteristics of human leg motion and its underlying motor-control scheme are studied through experiments and simulations, and a model of braking motion by the driver's leg is developed. This paper proposes novel brake systems based on two new aspects. First, the mechanical impedance characteristics of the leg action of the driver are taken into consideration in designing the brake systems. Second, the brake systems provide the driver with kinesthetic feedback of braking conditions or performance. The effectiveness of the proposed designs in a combined driver-vehicle system is investigated using driving simulation.

Genetic associations of prolificacy with performance, carcass, meat quality, and leg conformation traits in the Finnish Landrace and Large White pig populations.

The objective of this study was to estimate genetic associations of prolificacy traits with other traits under selection in the Finnish Landrace and Large White populations. The prolificacy traits evaluated were total number of piglets born, number of stillborn piglets, piglet mortality during suckling, age at first farrowing, and first farrowing interval. Genetic correlations were estimated with two performance traits (ADG and feed:gain ratio), with two carcass traits (lean percent and fat percent), with four meat quality traits (pH and L* values in longissimus dorsi and semimembranosus muscles), and with two leg conformation traits (overall leg action and buck-kneed forelegs). The data contained prolificacy information on 12,525 and 10,511 sows in the Finnish litter recording scheme and station testing records on 10,372 and 9,838 pigs in Landrace and Large White breeds, respectively. The genetic correlations were estimated by the restricted maximum likelihood method. The most substantial correlations were found between age at first farrowing and lean percent (0.19 in Landrace and 0.27 in Large White), and fat percent (-0.26 in Landrace and -0.18 in Large White), and between number of stillborn piglets and ADG (-0.38 in Landrace and -0.25 in Large White) and feed:gain (0.27 in Landrace and 0.12 in Large White). The correlations are indicative of the benefits of superior growth for piglets already at birth. Similarly, the correlations indicate that age at first farrowing is increasing owing to selection for carcass lean content. There was also clear favorable correlation between performance traits and piglet mortality from birth to weaning in Large White (r(g) was -0.43 between piglet mortality and ADG, and 0.42 between piglet mortality and feed:gain), but not in Landrace (corresponding correlations were 0.26 and -0.22). There was a general tendency that prolificacy traits were favorably correlated with performance traits, and unfavorably with carcass lean and fat percents, whereas there were no clear associations between prolificacy and meat quality or leg conformation. In conclusion, accuracy of estimated breeding values may be improved by accounting for genetic associations between prolificacy, carcass, and performance traits in a multitrait analysis.

Control of lateral weight-transfer initiation during sitting.

Whereas many researchers have examined the transition from quiet posture to dynamic state, study of the initiation of lateral weight-transfer during sitting has only begun recently. This action is included in many tasks performed in our daily living, i.e., reaching, dressing, looking backwards, lying down, and shuffling the buttocks. The present study was designed to describe lateral weight-transfer movements of healthy adults, kinematically and kinetically, and to clarify the strategies and speed dependency of lateral weight-transfer initiation during sitting. Seven healthy Japanese male students without orthopaedic or neurological disorders participated. Their lateral weight-transfer movements were measured during sitting, using two force platforms and a 3-dimensional analysis system. Analysis showed that there appear to be two strategies for the initiation of the task: one is the lateral bending of trunk toward the weight-transfer side, and the other is a coordinated reciprocal leg action of both legs. A combination of these strategies is used in a trade-off fashion during natural motions. These results are clinically important for the assessment and therapy of patients with sitting problems.

Evaluation of arm-leg coordination in flat breaststroke.

This study proposes a new method to evaluate arm-leg coordination in flat breaststroke. Five arm and leg stroke phases were defined with a velocity-video system. Five time gaps quantified the time between arm and leg actions during three paces of a race (200 m, 100 m and 50 m) in 16 top level swimmers. Based on these time gaps, effective glide, effective propulsion, effective leg insweep and effective recovery were used to identify the different stroke phases of the body. A faster pace corresponded to increased stroke rate, decreased stroke length, increased propulsive phases, shorter glide phases, and a shorter T1 time gap, which measured the effective body glide. The top level swimmers showed short time gaps (T2, T3, T4, measuring the timing of arm-leg recoveries), which reflected the continuity in arm and leg actions. The measurement of these time gaps thus provides a pertinent evaluation of swimmers' skill in adapting their arm-leg coordination to biomechanical constraints.

세단뛰기 지지국면 시 사지의 각운동량과 운동수행과의 관계

The purposes of this study were to determine the functions of actions of the limbs during each of the three support phases of the triple jump and their relationships with the performance of the triple jump. Four elite male triple jumpers were participated as subjects. The Pearson product moment correlation coefficient were used to determine and compare the relationships between the change in each component of the normalized angular momentum of the whole body about center of gravity and the actions of the extremities during different support phases. A level of significance at <TEX>$\alpha$</TEX>=.05 was set. After analyzing the angular momentum and correlation during support phase of the hop, step, and jump, the following findings are obtained: The actions of the arms created a side-somersaulting angular momentum about the whole body center of gravity toward the side of the free leg during the support phase of the step, and a somersaulting angular momentum about the whole body center of gravity during each support phase. The action of the free leg created a somersaulting angular momentum about the whole body center of gravity during the support phases of the hop and step.

Somatotopic Representation of Action Words in Human Motor and Premotor Cortex

Since the early days of research into language and the brain, word meaning was assumed to be processed in specific brain regions, which most modern neuroscientists localize to the left temporal lobe. Here we use event-related fMRI to show that action words referring to face, arm, or leg actions (e.g., to lick, pick, or kick), when presented in a passive reading task, differentially activated areas along the motor strip that either were directly adjacent to or overlapped with areas activated by actual movement of the tongue, fingers, or feet. These results demonstrate that the referential meaning of action words has a correlate in the somatotopic activation of motor and premotor cortex. This rules out a unified “meaning center” in the human brain and supports a dynamic view according to which words are processed by distributed neuronal assemblies with cortical topographies that reflect word semantics.

세단뛰기 지지국면 시 사지의 운동학적 변인과 전신 무게중심의 속도 변화와의 관계

The purposes of this study were to determine the functions of actions of the limbs during each of the three support phases of the triple jump and their relationships with the performance of the triple jump. Four elite male triple jumpers were participated as subjects. The statistical analyses used were the Pearson product moment correlation coefficient for establishing relationships and simple regression analyses to determine and compare the relationships between the change of the horizontal velocity and the change of the vertical velocity during different support phases. A level of significance at p<.05 was set. The actions of the arms were responsible for about 25%, 25%, and 30% of the decrease in the horizontal velocity of the whole body center of gravity during the support phases of the hop, step, and jump, respectively. The change in the velocities of the whole body center of gravity due to the actions of the free limbs were significantly related with the whole body center of gravity during each support phase. The action of the support leg was associated with the decrease in the horizontal velocity and the increase in the vertical velocity of the whole body center of gravity during each support phase.

The genetics of leg weakness in Finnish Large White and Landrace populations

Data from six progeny-testing (1994–1997) and one performance-testing (1991–1998) stations were compiled and subsequently used in the estimation of genetic parameters for overall leg action and the five most severe symptoms of leg weakness: buck-kneed, small inner claws, legs turned out on the fore legs, small inner claws and upright pasterns on the hind legs. Overall leg action was assessed using a scale from 1 to 5. Leg traits were recorded differently in the testing methods (four classes in the progeny-testing and two classes in the performance-testing). Observations used for analysis were rescaled into frequency normalised scores. Final data contained records of 6115 Large White (LW) and 7043 Landrace (LR) pigs. Pedigree information included all animals born after the year 1986. Variance components were estimated by the restricted maximum likelihood method, using a statistical model that included additive genetic animal and litter as random effects and interactions between station∗year∗season as a fixed effect. Heritability estimates were low for overall leg action (0.06 for LR and 0.05 for LW) and low to moderate (0.01–0.17) for individual leg traits. The proportion of variance due to common litter environment ranged from 0.03 to 0.14, and in all cases was significantly greater than zero. There was a strong genetic correlation between buck-kneed on the fore legs and overall leg action (0.88±.07 in LR and 0.98±.09 in LW), whereas correlations between other traits were highly variable across breeds and had large standard errors. Overall leg action and buck-kneed on the fore legs were unfavourably correlated with fat and lean percentages, whereas standard errors of the other genetic correlations between leg and production traits were too high to allow conclusions to be drawn.

New protective system preventing self-mutilation of rat surgical sites.

The paper presents a new approach to the rat self-mutilation mechanism, and introduces an appropriate protective system. Observations revealed that rats use three main implements to damage experimental sites, i.e., their teeth, forelegs, and hind legs. Ignoring even one of these factors diminishes the reliability of a protective system. Commonly used rat vests sometimes fail, since free fore- and hind legs may damage the system itself or the surgical area directly. A new system was designed to avoid these problems. A splint is glued to the fur of the rat neck and chest with fast-bonding glue, to prevent flexing the neck. Then, a vest is fabricated by wrapping adhesive tape around the chest and neck. One of the forelegs is immobilized by incorporating it into the tape vest. The action of the hind legs is neutralized by taping the feet with toes flexed. Such a protective system design is more reliable than those previously proposed, since teeth, forelegs, and hind legs are all prevented from self-mutilation. In addition, the tape vest and mittens fit the rat body well, and are easy to apply.

Sensorimotor pathways involved in interjoint reflex action of an insect leg

Coordination of motor output between leg joints is crucial for the generation of posture and active movements in multijointed appendages of legged organisms. We investigated in the stick insect the information flow between the middle leg femoral chordotonal organ (fCO), which measures position and movement in the femur-tibia (FT) joint and the motoneuron pools supplying the next proximal leg joint, the coxa-trochanteral (CT) joint. In the inactive animal, elongation of the fCO (by flexing the FT joint) induced a depolarization in eight of nine levator trochanteris motoneurons, with a suprathreshold activation of one to three motoneurons. Motoneurons of the depressor trochanteris muscle were inhibited by fCO elongation. Relaxation signals, i.e., extension of the FT joint, activated both levator and depressor motoneurons; i.e., both antagonistic muscles were coactivated. Monosynaptic as well as polysynaptic pathways contribute to interjoint reflex actions in the stick insect leg. fCO afferents were found to induce short latency EPSPs in levator motoneurons, providing evidence for direct connections between fCO afferents and levator motoneurons. In addition, neuronal pathways via intercalated interneurons were identified that transmit sensory information from the fCO onto levator and/or depressor motoneurons. Finally, we describe two kinds of alterations in interjoint reflex action: (a) With repetitive sensory stimulation, this interjoint reflex action shows a habituation-like decrease in strength. (b) In the actively moving animal, interjoint reflex action in response to fCO elongation, mimicking joint flexion, qualitatively remained the same sign, but with a marked increase in strength, indicating an increased influence of sensory signals from the FT joint onto the adjacent CT joint in the active animal.

Independent determination of symmetry and polarity in the Drosophila eye.

In each facet of the Drosophila compound eye, a cluster of photoreceptor cells assumes an asymmetric trapezoidal pattern. These clusters have opposite orientations above and below an equator, showing global dorsoventral mirror symmetry. However, in the mutant spiny legs, the polarization of each cluster appears to be random, so that no equator is evident. The apparent lack of an equator suggests that spiny legs+ may be involved in the establishment of global dorsoventral identity that might be essential for proper polarization of the photoreceptor clusters. Alternatively, a global dorsoventral pattern could be present, but spiny legs+ may be required for local polarization of individual clusters. Using an enhancer trap strain in which white+ gene expression is restricted to the dorsal field, we show that white+ expression in spiny legs correctly respects dorsoventral position even in facets with inappropriate polarizations; the dorsoventral boundary is indeed present, whereas the mechanism for polarization is perturbed. It is suggested that the boundary is established before the action of spiny legs+ by an independent mechanism.

成人女性における投能力向上の可能性

The purposes of this study were to clarify the possibility of progress of throwing ability on adult females, and to examine effective instructional methods of throwing. Twenty-four female students who had no special experiences of motor learning of throwing were divided into three groups; two training groups (WI group: throwing exercise with verbal instruction and demonstration, and NI group: throwing exercise without instruction) and one control group. Training was carried out three days per week for four weeks. Measuring physical fitness and analyzing throwing motions were performed before and after the training period. In the WI group, throwing distance increased significantly from 24.38 m to 30.38 m. Actions of arm and legs during preparatory phase of throwing were changed, consequently factors of action at starting of main phase of throwing were also changed. It seemed that these changes leaded to faster forward rotation of shoulder during main phase of throwing, skillful whip-like action and wrist action. In the NI group, throwing distance increased from 24.67 m to 27.17 m insignificantly. Remarkable changes of throwing motions were not recognized except for the increase of range of shoulder rotation. It is concluded that throwing distance and throwing motion are changed remarkably by throwing exercise with proper instructions of technique.

国民体育大会出場レベルの高校男子水球選手の整形外科的メディカルチェック

A six-month follow-up study of athletic injury and physical fitness was conducted on ten players in a nationally ranked boys' high school water polo team. The first medical check-up was conducted on May 28th, 1995, and the second just 4 days before the national athletic meet on September 2 nd. The final check-up was done on November 18 th. A thorough examination in addition to X-ray evaluation by an orthopedist was done on June 26th after the first medical check-up.In our check-ups, athletic injuries were defined as injuries due to water polo or disorders which prevented individuals from playing. In the thorough examination, athletic injuries included any physical conditions that required further investigations or treatment by the doctor.Six players had taken part in swimming before taking up water polo, and seven had played water polo since junior high school. Of the athletic injuries sustained, 55% occurred at the age of 13-14 yr. Injuries due to carelessness and over-enthusiasm amounted to six. Motion pain in the pes anserius, iliotibial tract, and hip joints without traumatic episodes were thought to originate from the characteristic leg action under the water.Although body weight and height varied among the players, the differences in the values of body fat percentage, body mass index, and lean body mass were slight.Since the players had few complaints, athletic injuries were difficult to find. However, with periodic medical check-ups and a thorough examination, we are able to prevent some problems such as pain in the pes anserius or iliotibialtract.

Involvement of eccentric muscle actions in giant slalom racing

Joint angular movements and muscle activation (EMG), were determined in male elite racers while performing the giant slalom. Movement cycles averaged 3.5 +/- 0.6 s (left plus right turn), and knee angle ranged 66-114 degrees (180 degrees = straight leg). Knee extensor muscle use was dominated (rectified EMG; P < 0.05) by the leg controlling the outside (downhill) ski during the turn. Time spent while decreasing knee angle (eccentric muscle action) of outside leg averaged 1.0 +/- 0.2 s. This phase was longer (P < 0.05) than the average push-off (concentric muscle action) phase of 0.5 +/- 0.1 s. Moreover, EMG activity of the outside leg during eccentric muscle actions exceeded (P < 0.05) that of concentric actions and was similar to that attained during maximum isometric knee extension in laboratory tests. Knee and hip angular movement ranged 20-50 degrees. Average joint velocities equalled 20-40 degrees.s(-1) during the turning phase. Thus, competitive giant slalom skiing is dominated by slow eccentric muscle actions performed at near maximum voluntary force. Because of their greater ability to generate force, eccentric muscle actions may be warranted or even required to resist the G-forces induced during the turn phase.

Comparative Morphology of Locomotion in Vertebrates

Abstract In the present study a unifying framework is proposed for the development of forms of locomotion in vertebrates. Four kinematic processes are identified that illustrate the divergence of modes of locomotion, from an ancestral undulatory lateral movement to the different modes seen in recent vertebrates: (a) Lateral movements of the segments of the trunk are incorporated, and then removed, in a cephalocaudal order; (b) a proximodistal transition is then evident, in which appendages (fins or legs), rather than the segments of the trunk, take over the task of active propulsion; (c) synchronized action of fore- and/or hind legs follows the primeval alternate action of legs; and (d) movements of the segments of the trunk in the vertical domain are incorporated to facilitate locomotion. These processes can be illustrated in the ontogeny of both amphibians and rodents: Lateral undulatory swimming in tadpoles is replaced during metamorphosis by synchronized hind leg strokes in toads and frogs; and pivoting around the hind legs, which is the primary quadrupedal activity in rats, is followed by alternate, and then simultaneous, stepping of the fore- and hind legs. The same processes may be applied to the development of locomotion in the different vertebrate classes, from the numerous species of fish that swim with lateral movements, to the widespread use of vertical movements in facilitating walking and swimming in mammals. When functional reasoning is ignored and only the form of locomotion is considered, a regular order in development is apparent.

Developmental sequences for hopping as assessment instruments: a generalizability analysis.

The purpose of this study was to investigate the generalizability with which undergraduate kinesiology and elementary education students can rate children's hopping performances according to prelongitudinally validated developmental sequences for the arms, legs, and total body. Twenty observers were assigned to one of four training groups (n = 5): (a) kinesiology students/total-body sequence, (b) kinesiology students/component sequences, (c) elementary education students/total-body sequence, and (d) elementary education students/component sequences. The observers rated five trials of videotaped hopping performances by 10 boys and 10 girls between the ages of 3.5 and 9.0 years. The results suggested that when kinesiology students receive 2 hours of training, one observer can reliably assess leg action in one trial (.80) and arm action in five trials (.80). In contrast, one elementary education student can reliably assess leg action within five trials (.80), but the average score of two observers assessing three trials each is needed to assess arm action (.81). Reliable assessment of total-body action requires two observers for both the kinesiology students (four trials each = .80) and the elementary education students (two trials each = .84).

Strength and Serviceability of Hanger Connections

Hanger connections involve bolts in tension due to direct loads and prying action and bending of tee flanges or angle legs. It is the purpose of this paper to show that the analysis method of the latest AISC Manuals, both ASD and LRFD versions, can with minor modification allow for a greatly increased design strength and a more reliable prediction of serviceability loads. The strength of hanger connections is due mainly to the strength of the bolts but is affected by the bending of the hanger flanges which induces prying action in the bolts. Previous emphasis on this problem has focused on the determination of the actual prying force Q rather than the overall behavior of the connection itself. This paper concentrates on assessing the strength of the connection, both ultimate strength and yield (or separation) strength.