Key factors in the development of lower limb co-ordination: implications for the acquisition of walking in children with cerebral palsy

PURPOSE

This paper explores differences in walking development between normal children and those with cerebral palsy and discusses their clinical implications.

METHOD

A literature review (MEDLINE, RECAL) of walking development in normal children and those with cerebral palsy, including the use of walking aids.

RESULTS

Normal neonates display reflexive stepping, at 8 months supported walking and then independent walking emerge at about 12 months. Transition from the wide-based, high stepping gait to narrower base, heel-toe gait with arm swing occurs within 6 months of walking. Gait is mature by 7 years. Children with cerebral palsy have delayed walking. Prognostic factors include retained reflexes, age of head control and of independent sitting. They retain kinematic and muscle activation patterns seen in supported walking. Older children show co-contraction patterns and lose range of motion at leg joints. Walking aids have been studied for energy consumption, but only independent walking patterns are described. Treadmills and partial weight relief have been used for walking training.

CONCLUSIONS

Children with cerebral palsy fail to achieve the transition from supported stepping to mature gait patterns. Assessment tools to identify gait maturity need to be developed so that treatment that promotes transitions can be promoted and effectively monitored.

Changes in mechanical work during severe exhausting running

The possible contribution of muscular work to the increase in oxygen uptake ( VO(2)) over time during running was investigated on 11 adult males who were asked to run until exhaustion at 90 (3)% [mean (SD)] of their maximal aerobic velocity on a treadmill ergometer. Ground reaction forces, expired gases and EMG from leg muscles were collected for 30 s at min 3 and during the last minute of the run. Subjects ran for 829 (165) s and showed an increase in VO(2 )of 179 (93) ml.min(-1) between min 3 and exhaustion. Increased ventilation explained 41 (27)% of the increase in VO(2). Stride frequency slightly decreased but no significant differences were found in the mechanical work or in integrated EMG. It was concluded that, in running, the increase in VO(2 )could not be related to a drift in muscle work.

An investigation of the interactions between lower-limb bone morphology, limb inertial properties and limb dynamics

Bone mass and size clearly affect the safety and survival of wild animals as well as human beings, however, little is known about the interactions between bone size and movement dynamics. A modeling approach was used to investigate the hypothesis that increased bone cortical area causes increased limb moments of inertia, decreased lower-limb movement maximum velocities, and increased energy requirements to sustain submaximum lower-limb locomotion movements. Custom software and digital data of a human leg were used to simulate femur, tibia, and fibula cortical bone area increases of 0%, 22%, 50%, and 80%. Limb segment masses, center of mass locations, and moments of inertia in the sagittal plane were calculated for each bone condition. Movement simulations of unloaded running and cycling motions were performed. Linear regression analyses were used to determine the magnitude of the effect cortical area has on limb moment of inertia, velocity, and the internal work required to move the limbs at a given velocity. The thigh and shank moment of inertia increased linearly up to 1.5% and 6.9%, respectively for an 80% increase in cortical area resulting in 1.3% and 2.0% decreases in maximum unloaded cycling and running velocities, respectively, and in 3.0% and 2.9% increases in internal work for the cycling and running motions, respectively. These results support the hypothesis and though small changes in movement speed and energy demands were observed, such changes may have played an important role in animal survival as bones evolved and became less robust.

Antisocial violent offenders with attention deficit hyperactivity disorder demonstrate akathisia-like hyperactivity in three-channel actometry

Actometry enables quantitative and qualitative analysis of various hyperactivity disorders. Antisocial violent offenders have demonstrated diurnal increases in motor activity that may be related to attention deficit hyperactivity disorder (ADHD) that often precedes antisocial development. Motor restlessness in ADHD has common features with neuroleptic-induced akathisia. In this study, three-channel actometry was used to compare 15 antisocial violent offenders who had a history of ADHD with 15 healthy control subjects and 10 akathisia patients. The Barnes Akathisia Rating Scale (BARS) was used for clinical evaluation of akathisia symptoms. Ankle movement indices and the ankle-waist ratio differentiated the antisocial patients from the healthy controls significantly, with no overlap, and the same parameters expectedly differentiated the akathisia patients from the healthy controls. The repetitive, rhythmic pattern of akathisia was found in 13 of the 15 antisocial patients. Nine of the antisocial patients scored 2 or 3 (mild to moderate akathisia) on the BARS. Thus, the motor hyperactivity of antisocial ADHD patients has common features with mild akathisia. This may be due to a common hypodopaminergic etiology of ADHD and akathisia.

Effect of creatine supplementation on body composition and performance: a meta-analysis

BACKGROUND

Creatine supplementation (CS) has been reported to increase body mass and improve performance in high-intensity, short-duration exercise tasks. Research on CS, most of which has come into existence since 1994, has been the focus of several qualitative reviews, but only one meta-analysis, which was conducted with a limited number of studies.

PURPOSE

This study compared the effects of CS on effect size (ES) for body composition (BC) variables (mass and lean body mass), duration and intensity (< or = 30 s, [ATP-PCr = A]; 30-150 s [glycolysis = G]; >150 s, [oxidative phosphorylation = O]) of the exercise task, type of exercise task (single, repetitive, laboratory, field, upper-body, lower-body), CS duration (loading, maintenance), and subject characteristics (gender, training status).

METHODS

A search of MEDLINE and SPORTDiscus using the phrase "creatine supplementation" revealed 96 English-language, peer-reviewed papers (100 studies), which included randomized group formation, a placebo control, and human subjects who were blinded to treatments. ES was calculated for each body composition and performance variable.

RESULTS

Small, but significant (ES > 0, p < or = .05) ES were reported for BC (n=163, mean +/- SE=0.17 +/- 0.03), ATP-PCr (n=17, 0.24 +/- 0.02), G (n=135, 0.19 +/- 0.05), and O (n=69, 0.20 +/- 0.07). ES was greater for change in BC following a loading-only CS regimen (0.26 +/- 0.03, p=.0003) compared to a maintenance regimen (0.04 +/- 0.05), for repetitive-bout (0.25 +/- 0.03,p=.028) compared to single-bout (0.18 +/- 0.02) exercise, and for upper-body exercise (0.42 +/- 0.07, p<.0001) compared to lower (0.21 +/- 0.02) and total body (0.13 +/- 0.04) exercise. ES for laboratory-based tasks (e.g., isometric/isotonic/isokinetic exercise, 0.25 +/- 0.02) were greater (p=.014) than those observed for field-based tasks (e.g., running, swimming, 0.14 +/- 0.04). There were no differences in BC or performance ES between males and females or between trained and untrained subjects.

CONCLUSION

ES was greater for changes in lean body mass following short-term CS, repetitive-bout laboratory-based exercise tasks < or = 30 s (e.g., isometric, isokinetic, and isotonic resistance exercise), and upper-body exercise. CS does not appear to be effective in improving running and swimming performance. There is no evidence in the literature of an effect of gender or training status on ES following CS.

Mobility and muscle strength contralateral to hemiplegia from stroke: benefit from self-training with family support

OBJECTIVE

To determine whether patient exercise with the support of family members maximizes mobility and improves muscle strength in the nonparetic lower limb after stroke.

DESIGN

Comparison of improvement at 2 wk between conventional exercise sessions and a program also including the participation of family members. Subjects were 60 patients rendered nonambulatory by severe hemiparesis from their first stroke. Of these, 42 had family members participating in their therapy. Lower limb strength was measured on the nonparetic side using an isokinetic machine. Mobility status was assessed using the Rivermead Mobility Index. Patients were evaluated at the first inpatient gym session and again at 1 and 2 wk.

RESULTS

At the first evaluation, lower limb strength and the Rivermead Mobility Index score did not differ between the two groups. Reevaluations were conducted at 1 and 2 wk after the first evaluation. Patients' strength and mobility improved more when family members participated.

CONCLUSION

Family participation is an important contributor to stroke rehabilitation.

Quantitative assessment of the stops walking while talking test in the elderly

OBJECTIVE

To examine whether trunk sway and walking speed differ between elderly "stoppers" and "nonstoppers" during a shorter version of the stops walking while talking (SWWT) test-an observational assessment of impaired dual-task performance-and during a normal walking trial.

DESIGN

The original SWWT test was administered on the way to the test room (over a distance of 150m). Then, subjects were asked to walk 2 trials of 8m while wearing a trunk sway measuring device strapped firmly to their lower back. For the first 8-m trial, no questions were asked (control trial). During the second 8-m trial, subjects were asked an easy question (What is your age?) after walking 2m.

SETTING

Long-stay geriatric care unit in Switzerland.

PARTICIPANTS

Seventeen institutionalized elderly (16 women, 1 man; mean age, 86.3y; range, 79-93y). Subjects had to be able to walk at least 150m and to understand simple questions.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

The amplitude of trunk sway angle and angular velocity in the forward-backward (pitch) and side-to-side (roll) directions and the duration of each trial were compared between the two 8-m walking trials with and without a question among subjects who did and did not come to a complete stop.

RESULTS

In the original SWWT test, 4 persons stopped walking while talking, compared with 8 persons who stopped in the short (8-m) walking trial when a question was asked. Persons who stopped during the 8-m trial when a question was asked had significantly longer walking durations (by 19s) and larger trunk roll angular displacements (by 5.5 degrees ) during trials, both with and without a question. For both stoppers and nonstoppers, duration was longer during the trial when a question was asked.

CONCLUSION

A fixed and brief walking distance, coupled with a single sudden question, provided an effective method of identifying subjects who stop walking while talking. These subjects are those who have slower walking speeds and more unstable trunk control in the roll plane even under normal walking conditions. Our findings support the predictive capabilities of a brief SWWT test for the unstable and fall-prone elderly, as well as the usefulness of objective trunk sway measures to identify gait instabilities.

Gender differences in lower extremity mechanics during running

OBJECTIVE

To compare differences in hip and knee kinematics and kinetics in male and female recreational runners.

DESIGN

Gait analysis of 20 men and 20 women recreational runners.

BACKGROUND

Female runners are reported to be more likely to sustain certain lower extremity injuries compared to their male counterparts. This has been attributed, in part, to differences in their structure and it has been postulated that these structural differences may lead to differences in running mechanics. It was hypothesized that females would exhibit greater peak hip adduction, hip internal rotation, knee abduction and decreased knee internal rotation compared to their male counterparts. It was also hypothesized that females would exhibit greater hip and knee negative work in the frontal and transverse planes compared to males.

METHODS

Comparisons of hip and knee three-dimentional joint angles and negative work during the stance phase of running gait were made between genders.

RESULTS

Female recreational runners demonstrated a significantly greater peak hip adduction, hip internal rotation and knee abduction angle compared to men. Female recreational runners also demonstrated significantly greater hip frontal and transverse plane negative work compared to male recreational runners.

CONCLUSION

Female recreational runners exhibit significantly different lower extremity mechanics in the frontal and transverse planes at the hip and knee during running compared to male recreational runners.

RELEVANCE

Understanding the differences in running mechanics between male and female runners may lend insight into the etiology of different injury patterns seen between genders. In addition, these results suggest that care should be taken to account for gender when studying groups of male and female recreational runners.

Effect of pedaling exercise on the hemiplegic lower limb

OBJECTIVE

To assess the effects of pedaling exercise on the muscle activities in hemiparetic lower limbs in patients with stroke.

DESIGN

In this before-and-after trial, 17 nonambulatory patients with chronic hemiparetic stroke were recruited. Using a servo-dynamically controlled ergometer with a trunk support, the patients pedaled at a resistance of 5 N-m at their comfortable speeds. Muscle activities were recorded with surface electrodes from bilateral quadriceps femoris, medial hamstrings, tibialis anterior, and medial gastrocnemius, and integrated electromyograms were used for analysis of muscle activity patterns during the pedaling cycle. Muscle activities during pedaling were compared with those during voluntary knee extension of the affected limb before, immediately after, and 30 min after the pedaling.

RESULTS

We found phasic muscle activities in the affected limb during pedaling that were antiphasic to the contralateral side. The muscle activities of quadriceps femoris and tibialis anterior increased significantly during pedaling compared with those during voluntary knee extension effort, whereas the muscle activity of medial hamstrings did not change. The postpedaling facilitation of quadriceps and tibialis anterior and the inhibition of gastrocnemius during voluntary knee extension effort lasted at least for 30 min.

CONCLUSION

Pedaling could facilitate phasic and coordinated muscle activities even in patients with severe hemiparesis, and it is potentially an effective mode of muscle reeducation.

Theories of bipedal walking: an odyssey

In this paper six theories of bipedal walking, and the evidence in support of the theories, are reviewed. They include: evolution, minimising energy consumption, maturation in children, central pattern generators, linking control and effect, and robots on two legs. Specifically, the six theories posit that: (1) bipedalism is the fundamental evolutionary adaptation that sets hominids--and therefore humans--apart from other primates; (2) locomotion is the translation of the centre of gravity along a pathway requiring the least expenditure of energy; (3) when a young child takes its first few halting steps, his or her biomechanical strategy is to minimise the risk of falling; (4) a dedicated network of interneurons in the spinal cord generates the rhythm and cyclic pattern of electromyographic signals that give rise to bipedal gait; (5) bipedal locomotion is generated through global entrainment of the neural system on the one hand, and the musculoskeletal system plus environment on the other; and (6) powered dynamic gait in a bipedal robot can be realised only through a strategy which is based on stability and real-time feedback control. The published record suggests that each of the theories has some measure of support. However, it is important to note that there are other important theories of locomotion which have not been covered in this review. Despite such omissions, this odyssey has explored the wide spectrum of bipedal walking, from its origins through to the integration of the nervous, muscular and skeletal systems.

Lower extremity muscle activities during cycling are influenced by load and frequency

The purpose of this experiment was to investigate the effects of frequency and inertia on lower extremity muscle activities during cycling. Electromyographic (EMG) data of seven lower extremity muscles were collected. Sixteen subjects cycled at 250 W across different cadences (60, 80, and 100 rpm) with different loads (0, 0.5, 1.0, 1.5, and 2.0 kg) attached to distal end of their thighs. Load and cadence interactions were observed for the offset of the biceps femoris (BF), the active duration of the rectus femoris (RF), and the peak magnitudes of the vastus lateralis (VL) and the tibialis anterior (TA). Cadence effects were observed in the onset of the gluteus maximus (GM), RF, BF, VL, and TA; the offset of the GM, RF, BF, VL; the duration of the BF and TA; the peak magnitude of the RF and gastrocnemius (GAS); and the crank angle at which the peak magnitude was achieved of the BF, GAS, and soleus (SOL). Load effect was observed from the onset of RF and SOL, the offset of RF, the duration of SOL, and the peak magnitude of BF. These results indicate that inertial properties influence the lower extremity muscular activity in addition to the cadence effect.

Data representation for joint kinematics simulation of the lower limb within an educational context

Three-dimensional (3D) visualization is becoming increasingly frequent in both qualitative and quantitative biomechanical studies of anatomical structures involving multiple data sources (e.g. morphological data and kinematics data). For many years, this kind of experiment was limited to the use of bi-dimensional images due to a lack of accurate 3D data. However, recent progress in medical imaging and computer graphics has forged new perspectives. Indeed, new techniques allow the development of an interactive interface for the simulation of human motions combining data from both medical imaging (i.e., morphology) and biomechanical studies (i.e., kinematics). Fields of application include medical education, biomechanical research and clinical research. This paper presents an experimental protocol for the development of anatomically realistic joint simulation within a pedagogical context. Results are shown for the lower limb. Extension to other joints is straightforward. This work is part of the Virtual Animation of the Kinematics of the Human project (VAKHUM) (http://www.ulb.ac.be/project/vakhum).

Foot orthotics affect lower extremity kinematics and kinetics during running

OBJECTIVE

To quantify the effects of posting and custom-molding of foot orthotics on lower extremity kinematics and kinetics during running.

DESIGN

Repeated measures.Background. Several kinematic and kinetic factors have been suggested to increase a runner's risk for injuries. It has been speculated that foot orthotics can be used to reduce injury related complaints or even prevent running injuries by affecting these factors.

METHODS

Twenty one volunteers participated in this study. Kinematic and kinetic variables obtained during overground running for medial posting, custom-molding, and the combination of medial posting and custom-molding of foot orthotics were compared to a control condition. Repeated measures ANOVA and student t-tests were used to detect significant differences (alpha=0.05).

RESULTS

Posting of foot orthotics reduced maximum foot eversion and ankle inversion moment and increased vertical loading rate and maximum knee external rotation moment (P<0.05). Molding and posting and molding reduced vertical loading rate and ankle inversion moment and increased maximum foot inversion and maximum knee external rotation moment (P<0.05).

CONCLUSIONS

The effects of posting and molding of foot orthotics are extremely different and when combining posting and molding, the effects of molding appear to be dominant. It yet remains to be determined whether posting or molding is more beneficial with respect to overuse running injuries.

RELEVANCE

The potential of foot orthotics for reducing pain and injuries is convincing. The current study provides valuable information about the role of specific structural components of foot orthotics and contributes to the knowledge about the mechanism underlying the effect of foot orthotics in running.

Effects of dynamic resistance training on heart rate variability in healthy older women

Twenty healthy women aged between 65 and 74 years, trained three times a week, for 16 weeks, on a cycle ergometer, to determine the effects of dynamic resistance training on heart rate variability (HRV). Subjects were allocated to two training groups, high (HI, n=10) and low (LO, n=10) intensity. The HI group performed eight sets of 8 revolutions at 80% of the maximum resistance to complete 2 pedal revolutions (2RM); the LO group performed eight sets of 16 pedal revolutions at 40% of 2RM. Subjects were tested twice before, as control period (-4 weeks and 0 weeks) and once after training (16 weeks) for HRV, maximum voluntary contraction (MVC) of knee extensors and peak power (P(p)) of lower limbs by jumping on a force platform. HRV was measured using time and frequency domain parameters. Two-way ANOVA for repeated measures was performed on all variables (P<0.05). Results showed no differences between training groups. Following training HRV was not modified, while MVC and P(p) significantly increased. The two proposed forms of dynamic resistance training were appropriate to improve muscle power and strength in elderly females without affecting HRV. More research should verify the effects of an isometric and more prolonged training stimulus on HRV in older subjects.

Lower-extremity biomechanics during forward and lateral stepping activities in older adults

OBJECTIVE

To characterize the lower-extremity biomechanics associated with stepping activities in older adults.

DESIGN

Repeated-measures comparison of kinematics and kinetics associated with forward step-up and lateral step-up activities.

BACKGROUND

Biomechanical analysis may be used to assess the effectiveness of various 'in-home activities' in targeting appropriate muscle groups and preserving functional strength and power in elders.

METHODS

Data were analyzed from 21 participants (mean 74.7 yr (standard deviation, 4.4 yr)) who performed the forward and lateral step-up activities while instrumented for biomechanical analysis. Motion analysis equipment, inverse dynamics equations, and repeated measures ANOVAs were used to contrast the maximum joint angles, peak net joint moments, angular impulse, work, and power associated with the activities.

RESULTS

The lateral step-up resulted in greater maximum knee flexion (P<0.001) and ankle dorsiflexion angles (P<0.01). Peak joint moments were similar between exercises. The forward step-up generated greater peak hip power (P<0.05) and total work (P<0.001); whereas, the lateral step-up generated greater impulse (P<0.05), work (P<0.01), and power (P<0.05) at the knee and ankle.

CONCLUSIONS

In older adults, the forward step-up places greater demand on the hip extensors, while lateral step-up places greater demand on the knee extensors and ankle plantar flexors.

RELEVANCE

Clinicians may use data from biomechanical analyses of in-home exercises to more effectively target specific lower-extremity muscle groups when prescribing exercise activities for older adults. The forward step-up is recommended for maintaining or improving hip extensor performance; whereas, the lateral step-up is recommended when targeting the knee extensors and ankle plantar flexors.

Frequency of occurrence of the F wave in distal flexor muscles as a function of hypnotic susceptibility and hypnosis

The aim of the experiment was to assess whether the membrane excitability of flexor cervical and/or lumbar motoneurons is related to hypnotic susceptibility (measured with the Stanford Hypnotic Susceptibility Scale, Form A) and hypnosis. During the experimental sessions, hypnotized subjects were given only suggestions of relaxation (neutral hypnosis) while awake subjects were given instructions to be quiet and relaxed (simple relaxation). F waves were recorded from the abductor digiti minimi and abductor hallucis of both sides after electrical stimulation of the ulnar or tibial nerve, respectively, and were used as an index of motoneuron membrane excitability in three groups of subjects: highly susceptible under neutral hypnosis, highly susceptible and non-susceptible during simple relaxation sessions. In lower limbs, there was no difference among the groups in the frequency of occurrence of F waves. In upper limbs, hypnosis selectively reduced F frequency of occurrence in flexor motoneurons on the right side. This reduction persisted after the end of hypnosis and also occurred during the last period of relaxation in highly susceptible non-hypnotized subjects. Results support the idea that hypnotic phenomena develop along a continuum in which some trait differences can be more easily revealed by the induction of hypnosis.

Optimum ratio of upper to lower limb lengths in hand-carrying of a load under the assumption of frequency coordination

The ratio of the upper to lower limb lengths [or the intermembral index (IMI)] in the earliest human ancestors is closer to that of the living chimpanzees than to our own, although the former show undoubted adaptations to bipedality. What biomechanical factors could then have led to the phenomenon of genus Homo? This paper proposes and evaluates a relationship between IMI and hand-carrying. Assuming that coordination of limb swing frequencies of the upper and lower limbs would be the subject of positive selection, a mathematical expression was derived and can in part explain the changes in IMI. We found that AL-288-1 [3.6 million years old (MY)], the most complete skeleton of the early hominid Australopithecus afarensis, could only have carried loads equivalent to 15-50% of the upper limb weight while maintaining swing symmetry, but KNM WT-15000, Homo ergaster (1.8MY) and modern humans could both carry loads 3 times heavier than the upper limb while maintaining swing symmetry. The carrying ability of chimpanzees would be inferior to that of AL-288-1. The IMI of modern humans, at 68-70, is the smallest, and is optimal for hand-carrying under our criteria. Under reduced selection pressure for hand-carrying, but unreduced selection for mechanical effectiveness, we might expect humans to evolve a longer upper limb, to improve swing symmetry when unloaded.

Ventilatory thresholds in arm and leg exercises with spontaneously chosen crank and pedal rates

The present study assessed whether the first and the second ventilatory thresholds (VT1 and VT2) were dependent on the muscle groups solicited when spontaneously chosen crank and pedal rates are used. 20 physical education male students (22 +/- 2.2 yr.) performed two maximal incremental tests randomly assigned using an increment of 15 and 30 W every minute for arm and leg exercises, respectively. These tests were used to measure the maximal oxygen uptake (VO2 max) and to identify VT1 and VT2. The absolute oxygen uptake (VO2) values measured at VT1, VT2, and at maximal workload were significantly (p < .05) lower during arm and leg exercises. However, VT1 and VT2 expressed in percent of VO2 max were not significantly different between arm and leg exercises (54.1 +/- 8.2 vs 57.2 +/- 11.4%; and 82.5 +/- 6.4 vs 84.6 +/- 5.1% at VT1 and VT2, respectively). In addition, at the two thresholds, none of the variables measured during arm and leg exercises were significantly correlated with the exception of spontaneously chosen crank and pedal rates (p < .01; r = .75 and r = .69 for VT1 and VT2, respectively). Probably due to the different training status and skill level, no extrapolation can be made to specify the arm thresholds from the leg. These results underline the need to specify the ventilatory thresholds from specific arm ergometer measures obtained from tests performed with spontaneously chosen crank and pedal rates and, thus, close to sport and recreational activities, when they are used for training and rehabilitation programs.

Three-dimensional kinetic analysis of side-foot and instep soccer kicks

PURPOSE

The purpose of this study was to identify the kinetic aspects of side-foot and instep soccer kicks to understand the different mechanics underlying the two kicks.

METHODS

The motions of both kicks were captured using a three-dimensional cinematographic technique. The kicking leg was modeled as a three-link kinetic chain composed of thigh, shank, and foot, from which joint torques and angular velocities were computed.

RESULTS

The ball velocity of the side-foot kick (23.4 +/- 1.7 m x s(-1)) was significantly slower than that of the instep kick (28.0 +/- 2.1 m.s(-1)). Significant differences were also observed between the two kicks for the magnitude of hip external rotation torque (56 +/- 12 N.m in the side-foot kick; 33 +/- 8 N.m in the instep kick) and hip external rotation angular velocity (11.1 +/- 2.4 rad x s(-1) in the side-foot kick; 6.0 +/- 2.0 rad x s(-1) in the instep kick).

CONCLUSION

These results indicated that to hit the ball with the medial side of the foot, a complicated series of rotational motions are required for the side-foot kick. The hip external rotation torque dominantly exhibited in the side-foot kick caused the clockwise rotation of the thigh-shank plane at the later stage of kicking. This may allow the hip external rotation motion to increase directly the forward velocity of the side foot, with which players can squarely impact the ball.

Effects of vibration in inline skating on the Hoffmann reflex, force, and proprioception

PURPOSE

The objective of this study was to examine the effects of vibrations induced by inline skating on the Hoffmann (H) reflex, maximal voluntary isometric (MVC) force, and ankle proprioception.

METHODS

Accelerometers were used to measure the frequencies and amplitudes of the vibrations encountered at the skate and mid-tibia levels. The soleus H reflex was recorded before and after (for 30 min) inline skating for 30 min. Maximal plantarflexor contractions were performed against a strain gauge while EMG was recorded from the soleus and medial gastrocnemius muscles. An ankle position-matching test was carried out to measure proprioception at the ankle. A Modified Borg Scale was used to obtain the appreciation of leg numbness and fatigue during inline skating.

RESULTS

The vibrations measured at the skate chassis level had a mean frequency of 141.8 +/- 25.2 Hz and an amplitude of </=5 g. These vibrations were transmitted to the lower limb as measured by a mean frequency of 34.4 +/- 27.7 Hz and an amplitude of </=2 g at the mid-tibia level. The results demonstrate a clear inhibition ( approximately 35%) of the H reflex after skating that persisted for >35 min after skating. A 10% drop in MVC plantarflexor force was observed after inline skating. There was no accompanying change in EMG signal parameters. The ankle proprioception of the subjects decreased after skating, resulting in reproduction errors twice as large as before skating.

CONCLUSION

Vibrations encountered during inline skating resulted in modifications of neuromotor functions related to the muscle spindles' primary afferent. These changes may partially be explained by presynaptic inhibition; however, a more plausible mechanism may be a decrease in the Ia afferent transmission induced by the vibration.

Electromyographic validation of the double pulley equipment during movements of the lower limbs

The double pulley equipment was tested on ten male volunteers during contraction of the semitendinosus and biceps femoris (caput longum) muscles in the following movements of the lower limbs: 1) hip extension with extended knee and erect trunk, 2) hip extension with flexed knee and erect trunk, 3) hip extension with flexed knee and erect trunk, 3) hip extension with extended knee and inclined trunk, 5) hip abduction along the midline, 7) hip abduction with extension beyond the midline, 8) adduction with hip flexion beyond the midline, 8) adduction with hip flexion beyond the midline, and 9) adduction with hip extension beyond the midline. The myoelectric signals were taken up by Lec Tec surface electrodes connected to a 6-channel Lynx electromyographic signal amplifier coupled with a computer equipped with a model CAD 10/26 analogue digital conversion board and with a specific software for signal recording and analysis. The semitendinosus and biceps femoris muscles presented the highest potentials in movements 1; 2; 7, 8 and 9, whereas the potentials in the remaining movements were negligible. The pattern of activity of the semitendinosus and the biceps femoris was similar in exercises 1, 2, 3, 4 and 8. The potentials of the semitendinosus prevailed in movements 5, 6 and 7, and the strongest potentials observed in movement 9 were those of the biceps femoris.

Effects of standing and sitting on finger-tapping speed in healthy adults

STUDY DESIGN

A repeated-measures design was used to compare finger-tapping performance (hand functional control) across 4 standing and sitting conditions of limb body support postures.

OBJECTIVES

The intent was to examine the hypothesized hemispheric control interference effects of lower limb body support postures on finger-tapping performance. A secondary objective was to gain a better understanding of the relationship between lower limb posture and concurrent finger-tapping activity.

BACKGROUND

In a task such as kicking a ball with the right foot, foot control theory suggests that the left hemisphere contralaterally controls right-foot kicking action. However, it can also be interpreted that the postural support (with the left foot in this example) involving the action of antigravity muscles (leg extensors) is driven ipsilaterally. Based on this explanation, we would expect a hemispheric effect to occur during standing on the left limb while performing a finger-tapping task with the right hand. This study has theoretical and clinical significance for understanding hemispheric and functional control of limbs, which may underlie the assessment of movement control and the development and use of therapeutic interventions that can potentially improve functional movement control.

METHODS AND MEASURES

Ninety-eight (98) adult participants (ages 19 to 32 years) performed a finger-tapping task in 4 postural conditions: seated, standing on both feet, standing on the right foot only (RF), and standing on the left foot only (LF).

RESULTS

As predicted, manual performance was significantly slower in the LF condition as compared to the standing and sitting positions. However, when comparing performance between the LF and RF conditions, the difference was minimal.

CONCLUSIONS

Although support for the ipsilateral effect was not found, postural position did influence manual performance.

Understanding muscle coordination of the human leg with dynamical simulations

Muscles coordinate multijoint motion by generating forces that cause reaction forces throughout the body. Thus, a muscle can redistribute existing segmental energy by accelerating some segments and decelerating others. In the process, a muscle may also produce or absorb energy, in which case its summed energetic effect on the segments is positive or negative, respectively. This Borelli Lecture shows how dynamical simulations derived from musculoskeletal models reveal muscle-induced segmental energy redistribution and muscle co-functions and synergies. Synergy occurs when co-excited muscles distribute segmental energy differently to execute the motor task. In maximum height jumping, high vertical velocity at lift-off occurs desirably at full body extension because biarticular leg muscles redistribute the energy produced by the uniarticular leg muscles. In pedaling, synergistic ankle plantarflexor force generation during leg extension allows the high energy produced by the uniarticular hip and knee extensors to be delivered to the crank. An analogous less-powerful flexor synergy exists during leg flexion. Hamstrings reduce crank deceleration during the leg extension-to-flexion transition by not only producing energy but delivering it to the crank through its contribution to the tangential (accelerating) crank force, though this hamstrings function occurs at the opposite (flexion-extension) transition when pedaling backwards. In walking, the eccentric quadriceps activity in early stance not only decelerates the leg but also accelerates the trunk. In mid-stance, the uni- and biarticular plantarflexors, by having opposite segmental energetic effects, act in synergy to support the whole body, so segmental potential and kinetic energy exchange can occur. To conclude, the extraction of unmeasurable variables from dynamical simulations emulating task kinematics, kinetics, and EMGs shows how the production of force and energy by individual muscles contribute to the energy flow among the individual segments during task execution.

Electrical foot stimulation and implications for the prevention of venous thromboembolic disease

BACKGROUND

Venous stasis caused by immobility is an important risk factor for deep vein thrombosis following surgery and lower limb trauma, in bed-ridden medical patients, and in high-risk long distance air travelers. A safe and convenient method for reducing venous stasis would be useful in patients while in hospital and after discharge during their rehabilitation.

SUBJECTS AND METHODS

49 healthy subjects aged 51-76 were seated for 4 hours during which they received mild electrical stimulation of the calf, or sole of the foot (plantar muscles). Popliteal and femoral venous blood flow velocities were measured via doppler ultrasound. The non-stimulated lower extremity served as the simultaneous control. Subjects completed a questionnaire regarding their acceptance and tolerance of the electrical stimulation.

RESULTS

There was a significant increase in venous femoral and popliteal blood flow for both calf (p < 0.035, p < 0.003), and plantar muscles (p < 0.0001, p < 0.009) on the stimulated side compared to the unstimulated side. The magnitude of the effect was similar for calf and plantar muscle stimulation. Subjects did not find the experience uncomfortable, and would use an electrical stimulator if told by their physician that they were at risk for developing blood clots.

CONCLUSIONS

Mild electrical stimulation of the feet, as well as the calf, is a safe effective and convenient method for counteracting venous stasis and therefore has the potential to reduce the risk of deep vein thrombosis and pulmonary embolism for subjects who are immobilized.