Does wearing unstable shoes reduce low back pain and disability in nurses? A randomized controlled pilot study.

OBJECTIVE: To evaluate if wearing unstable shoes reduces low back pain and disability in nurses. DESIGN: A randomized controlled trial. SETTING: Hospitals and homecare. SUBJECTS: A total of 20 matched female registered nurses with low back pain. The mean (standard deviation) age was 31 years (5) for the control and 34 years (6) for the intervention group; height was 161 cm (5) and 165 cm (7), respectively. INTERVENTIONS: The intervention group received unstable shoes at Week 2 to wear for at least 36 h/week for a month. MAIN MEASURES: The Oswestry Low Back Pain Disability Questionnaire and a visual analogue pain scale. RESULTS: The mean (standard deviation) pain level was 6 (1) at baseline vs. 6 (2) at Week 6 for the control group, and 5 (1) vs. 1 (1) for the intervention group. The mean (standard deviation) disability level was 31% (9) at baseline vs. 28% (7) at Week 6 for the control, and 27% (12) vs. 13% (5) for the intervention group. There were no significant changes over time on pain or disability levels for the control group. The intervention group reported lower levels of pain on Weeks 4 (mean difference ⩾-1.4, p ⩽ 0.009) and 6 (mean difference ⩾-3.1, p < 0.001). Disability levels were also lower on Weeks 4 (mean difference = -4.5%, p NS) and 6 (mean difference = -14.1%, p = 0.020). CONCLUSIONS: Wearing unstable shoes reduced low back pain and disability in nurses and might be helpful as part of the back pain rehabilitation process.

Evaluation of eye, head and trunk coordination during target tracking tasks.

This study tested the feasibility of a method to synchronise and to evaluate eye, head and trunk movement patterns during target tracking tasks performed by 10 subjects. A projected central target was randomly repositioned at 40° and 70° of rotation to the left and right. Subjects were instructed to change gaze as quickly as possible. Head and trunk motion was measured using a motion analysis system, and eye movement was measured using an eye-tracker; all data were synchronised. For healthy subjects, the eye moved faster than the head, there was no trunk movement and the head moved more than the eye to reach further displaced targets. The method tested was feasible, and it could be used to evaluate eye, head and trunk movement patterns of subjects with injuries such as whiplash and concussions. Practitioner Summary: Studies of eye, head and trunk movements using synchronised methods are needed. We tested the feasibility of a method to synchronise and evaluate eye, head and trunk movement patterns. The method tested was feasible, and it could be used to evaluate movement patterns of subjects with injuries such as whiplash.

The influence of accuracy constraints on EMG and kinetic variables during gait initiation.

[Purpose] This study investigated the effects of accuracy constraints (targets) placed on the stepping-limb heel-strike (HS) on the electromyogram (EMG) and ground reaction forces (GRFs) during gait initiation. [Subjects and Methods] Twenty healthy subjects (29.2 ± 2.9 years) were asked to begin walking or stepping over a 10-cm-high obstacle at a fast speed. A 3-cm-diameter target was placed on the ground to dictate the position and accuracy of the stepping-limb HS. [Results] The results showed that the initiation velocity increase in the no-target conditions was due to modulation of the stance- and stepping-limb GRFs and a corresponding increase in the tibialis anterior (TA) activities of both limbs before stepping-limb toe-off. This was achieved by significantly increasing the stepping- and stance-limb TAEMG1 (determined between the onset of movement and time to peak anteroposterior (A-P) GRF of the stepping- and stance- limb) for the no-target conditions. It seems, therefore, that TAEMG1 and the slope to stepping-limb peak A-P GRF contributed to the intended velocity of initiation. [Conclusion] These data indicate that gait initiation and/or stepping over an obstacle may prove to be tasks by which motor control can be measured. The present study provides insight into the working mechanisms of the stepping and stance limbs and shows a clear need to further investigate whether the intact or affected limb should be used to initiate gait during rehabilitation and prosthetic training.

Functional and psychosocial status of Haitians who became users of lower extremity prostheses as a result of the 2010 earthquake.

The January 12, 2010 earthquake devastated Port-Au-Prince, the capital of the Republic of Haiti, and its surroundings. Among the 300,000 injured, 1,200 to 1,500 people underwent traumatic /surgical amputations. The purpose of this study was to describe the functional and psychosocial impact of prostheses users who suffered a traumatic lower-limb amputation after the earthquake of 2010 in Haiti. We recruited 140 participants in collaboration with a large health care organization in Port-au-Prince from October 2011 to May 2012. Participants underwent an evaluation of physical impairments and completed questionnaires translated into Haitian Creole. The Trinity Amputation and Prosthesis Experience Scale (TAPES), and the Locomotor Capabilities Index (LCI) were used in this study. The questionnaires were administered verbally in Haitian Creole by a trained staff. We conducted descriptive statistics and t-tests using SPSS for data analysis. Participants had a mean age of 34.9 ± 12.0; 51.4% were women; 48.6% were transfemoral amputees. The mean of TAPES general adjustment (3.65 ± 0.59) and adjust to limitation (3.67 ± 0.86) were higher than the score for the social adjustment (2.58 ± 0.49). The LCI showed over 90% of subjects were physically independent in self-care; fewer were independent walking on uneven ground or inclement weather (69%). The relatively poor social adjustment is consistent with the literature that describes limited acceptance of people with physical disabilities in Haitian society. Prostheses users in Haiti would benefit from a health delivery infrastructure that also addresses the psychosocial reintegration of individuals with physical disabilities.

Do people with Parkinson's disease change strategy during unplanned gait termination?

In light of the movement control problems reported for patients with Parkinson's disease (PD), we examined the lower extremity control strategies used by these subjects to stop walking in planned and unplanned situations. We compared how patients with PD and age and gender-matched control subjects modulated lower extremity muscular activity and ground reaction forces during planned and unplanned stoppings. The main findings were that control subjects did not alter muscle activation from planned to unplanned stopping, relative to stance limb kinetic events; they just increased the amplitude of the response (by approximately 800%). We speculate that these data provide preliminary evidence in support of a stereotypical sequence of muscle activation for gait termination whether planned or unplanned. In contrast, subjects with PD appeared to adopt a different strategy when stopping unexpectedly compared to planned stopping. Additional data show that subjects with PD required additional steps to stop walking when stopping unexpectedly as compared to control subjects.

Athletic footwear, leg stiffness, and running kinematics.

CONTEXT: The leg acts as a linear spring during running and hopping and adapts to the stiffness of the surface, maintaining constant total stiffness of the leg-surface system. Introducing a substance (eg, footwear) may affect the stiffness of the leg in response to changes in surface stiffness. OBJECTIVE: To determine if the type of athletic footwear affects the regulation of leg stiffness in dynamic activities. DESIGN: Repeated-measures design. SETTING: Motion analysis laboratory. PATIENTS OR OTHER PARTICIPANTS: Nine healthy adults (age = 28 +/- 6.8 years, mass = 71.6 +/- 12.9 kg) free from lower extremity injuries. INTERVENTION(S): Subjects hopped at 2.2 Hz on a forceplate under 3 footwear conditions (barefoot, low-cost footwear, high-cost footwear). Subjects ran on a treadmill at 2 speeds (2.23 m/s, 3.58 m/s) under the same footwear conditions. MAIN OUTCOME MEASURE(S): Limb stiffness was calculated from forceplate data. Kinematic data (knee and ankle angles at initial contact and peak joint excursion after contact) were collected during running. We calculated 1-way repeated-measures (stiffness) and 2-way (speed by footwear) repeated-measures analyses of variance (running kinematics) to test the dependent variables. RESULTS: A significant increase in leg stiffness from the barefoot to the "cushioned" shoe condition was noted during hopping. When running shod, runners landed in more dorsiflexion but had less ankle motion than when running barefoot. No differences were seen between the types of shoes. The primary kinematic difference was identified as running speed increased: runners landed in more knee flexion. At the ankle, barefoot runners increased ankle motion to a significantly greater extent than did shod runners as speed increased. CONCLUSIONS: Footwear influences the maintenance of stiffness in the lower extremity during hopping and joint excursion at the ankle in running. Differences in cushioning properties of the shoes tested did not appear to be significant.

Work-related musculoskeletal disorders among physical therapists: A systematic review.

Physical therapists (PTs) perform demanding tasks that can lead to work-related musculoskeletal disorders (WMSD), but the rates and characteristics of WMSD among PTs are not well known. The objective of this systematic review of the literature was to integrate the information published on the prevalence, types, and risks for WMSD among PTs. Four databases were searched using combinations and synonyms for WMSD, discomfort, symptoms, and PTs. Two reviewers independently searched and screened peer-reviewed articles published in English evaluating WMSD in PTs; agreement between reviewers was evaluated. From 867 unduplicated articles, 32 were eligible and included. Up to 90% of PTs have WMSD during their careers; 50% experience WMSD within 5 years of practice. Low back was the body part most commonly affected. Female PTs and PTs working in hospitals have higher prevalence of WMSD. WMSD are associated with PTs' age, gender, specialty and job tasks. Performing manual therapy, lifting and transferring patients are tasks commonly associated with PTs' developing WMSD. The body parts affected differed by specialty and tasks. The findings presented in this review are useful to inform future research, quality improvement, and educational programs to reduce the rates of WMSD among PTs.

Work-related musculoskeletal disorders among physical therapists: an online survey.

PURPOSE: To evaluate the rates and characteristics of musculoskeletal disorders (MSDs) in physical therapists (PTs) according to their specialty and setting. METHOD: Participants completed an online questionnaire including 15 demographic questions, 7 work-related and 8 injury-related questions for 9 different body parts. RESULTS: Complete responses were obtained from 121 PTs; 96% reported MSD symptoms during the previous 12 months, 64% affecting at least 3 body parts. The body parts with the highest prevalence of symptoms were the low back (66%) and the neck (61%). For PTs specialized in acute care, geriatrics and pediatrics, the body part most commonly affected was the low back, while for PTs specialized in orthopedics and neurology, the body part most commonly affected was the neck. Regarding work settings, the low back was the most commonly affected for PTs working in skilled nursing facilities, outpatient clinics and hospitals, and the neck in PTs working in academic and home health settings. CONCLUSIONS: MSDs are common among PTs; the body parts most often affected were the low back and neck. The prevalence and body parts affected varied by practice setting and specialty area. The findings can help informing the design of evidence-based rehabilitation, prevention, training and educational programs. IMPLICATIONS FOR REHABILITATION: Rehabilitation of injured physical therapists needs to address the symptoms of the multiple body parts that are usually affected (e.g. back, wrists and hands). Rehabilitation of injured physical therapists needs to take into consideration their job demands, practice setting and specialty area. The findings can inform the design of rehabilitation, prevention, training and educational programs for physical therapists.

Effects of wearing an ankle brace on ground reaction forces during jumps in basketball game simulation / Efectos del uso de órtesis de tobillo sobre las fuerzas de reacción del suelo durante los saltos en simulación de juego de baloncesto / Efeitos do uso de órtese de tornozelo sobre as forças de reação do solo durante saltos em simulação do jogo de basquetebol

ABSTRACT Introduction: The use of ankle braces reduces the risk of ankle injuries in basketball players. However, the mechanisms of injury protection provided by the ankle braces in the basketball game are still unknown. Objectives: To analyze the effects of wearing a lace-up ankle brace, and to conduct an exercise protocol that simulated the intensity of the basketball game on ground reaction force (GRF) during basketball-specific vertical jumps. Methods: Eleven male younger basketball players aged under 18 completed 48 vertical jumps, with and without ankle braces, during an exercise protocol composed of four 10-minute periods, simulating the activity profile and intensity of the basketball game as well as the typical intervals between periods. Mediolateral (variables: the greatest medial and lateral peaks) and vertical (variables: vertical peak, impulse peak, impulse at 50 ms of landing, loading rate and jump height) GRF were measured during takeoff and landing for all the jumps performed in the exercise protocol. Results: The use of the ankle brace reduced mediolateral GRF in all periods of the exercise protocol during takeoff and landing ( P < 0.05), without affecting the vertical GRF ( P > 0.05). Mediolateral and vertical GRF (takeoff mediolateral vertical peaks, landing mediolateral peaks, landing impulse peak, takeoff and landing loading rate) increased significantly during four subsequent 10-minute periods ( P < 0.05). However, for mediolateral GRF, the increase overtime was higher without braces. Conclusions: The use of the ankle brace reduced the mediolateral GRF on the lower limb, while there was a progressive increase in the external load applied to the body during the vertical jumps in the subsequent periods of the exercise protocol performed at the same intensity of the basketball game. Level of evidence I; Randomized clinical trial .

RESUMEN Introducción: El uso de órtesis de tobillo reduce el riesgo de lesiones en el tobillo en jugadores de baloncesto. Sin embargo, los mecanismos de protección de lesión proporcionados por las órtesis durante el juego de baloncesto aún son desconocidos. Objetivos: Analizar el efecto del uso de órtesis de tobillo lace-up (con cordón) y de un protocolo de ejercicio que simuló la intensidad del juego de baloncesto sobre la fuerza de reacción del suelo (FRS) durante saltos verticales específicos del baloncesto. Métodos: Once jugadores de baloncesto del sexo masculino con menos de 18 años realizaron 48 saltos verticales, con y sin órtesis de tobillo, durante un protocolo de ejercicios compuesto por cuatro períodos de 10 minutos, que simularon el perfil de actividad e intensidad del juego de baloncesto, así como los intervalos típicos entre los períodos. Las FRS mediolaterales (variables: mayores picos medial y lateral) y verticales (variables: pico vertical, pico de impulso, impulso en 50 ms de aterrizaje, tasa de sobrecarga y altura del salto) fueron medidas durante las fases de despegue y aterrizaje de todos saltos realizados en el protocolo de ejercicio. Resultados: El uso de órtesis redujo la FRS mediolateral en todos los períodos analizados, durante las fases de despegue y aterrizaje (P < 0,05), sin afectar la FRS vertical (P > 0,05). La FRS mediolateral y vertical (picos mediolateral y vertical de despegue, picos mediolaterales de aterrizaje, pico de impulso de aterrizaje, tasa de sobrecarga en el despegue y aterrizaje) aumentaron significativamente durante cuatro períodos subsiguientes de 10 minutos (P < 0,05). Sin embargo, para la FRS mediolateral, el aumento a lo largo del tiempo fue mayor sin el uso de órtesis. Conclusiones: El uso de órtesis de tobillo redujo la FRS mediolateral en el miembro inferior, mientras que hubo un aumento progresivo de la carga externa aplicada al cuerpo durante los saltos en los períodos subsiguientes del protocolo de ejercicios con la misma intensidad del juego de baloncesto. Nivel de evidencia I; Ensayo clínico aleatorizado.

RESUMO Introdução: O uso de órtese de tornozelo reduz o risco de lesões no tornozelo em jogadores de basquetebol. No entanto, os mecanismos de proteção de lesão fornecidos pelas órteses durante o jogo de basquetebol ainda são desconhecidos. Objetivos: Analisar o efeito do uso de órtese de tornozelo lace-up (com cordão) e de um protocolo de exercício que simulou a intensidade do jogo de basquetebol sobre a força de reação do solo (FRS) durante saltos verticais específicos do basquetebol. Métodos: Onze jogadores de basquetebol do sexo masculino com menos de 18 anos realizaram 48 saltos verticais, com e sem órtese de tornozelo, durante um protocolo de exercícios composto por quatro períodos de 10 minutos, que simularam o perfil de atividade e intensidade do jogo de basquetebol, assim como os intervalos típicos entre os períodos. As FRSs mediolaterais (variáveis: maiores picos medial e lateral) e verticais (variáveis: pico vertical, pico de impulso, impulso em 50 ms da aterrissagem, taxa de sobrecarga e altura do salto) foram medidas durante as fases de decolagem e aterrissagem de todos os saltos realizados no protocolo de exercício. Resultados: O uso de órtese reduziu a FRS mediolateral em todos os períodos analisados, durante as fases de decolagem e aterrissagem (P < 0,05), sem afetar a FRS vertical (P > 0,05). A FRS mediolateral e vertical (picos mediolateral e vertical de decolagem, picos mediolaterais de aterrissagem, pico de impulso de aterrissagem, taxa de sobrecarga na decolagem e aterrissagem) aumentaram significativamente durante quatro períodos subsequentes de 10 minutos (P < 0,05). No entanto, para a FRS mediolateral, o aumento ao longo do tempo foi maior sem o uso de órtese. Conclusões: O uso de órtese de tornozelo reduziu a FRS mediolateral no membro inferior, enquanto houve um aumento progressivo da carga externa aplicada ao corpo durante os saltos nos períodos subsequentes do protocolo de exercícios com mesma intensidade do jogo de basquetebol. Nível de evidencia I; Estudo clínico randomizado .

Knee biomechanics during landings: comparison of pre- and postpubescent females.

PURPOSE: The purpose of this investigation was to examine lower-extremity biomechanical differences between prepubescent and postpubescent female recreational athletes during three drop jump-landing sequences (static landing, vertical landing, and lateral landing) to determine whether maturation influenced injury risk. METHODS: Sixteen recreationally active postpubescent women (18-25 yr of age) and 16 recreationally active girls (8-11 yr of age) participated in this study. High-speed three-dimensional videography and force plate data were recorded for each subject's performance of the landing tasks and an inverse dynamics procedure was used to estimate knee joint resultant moments and forces. Kinematic and kinetic dependent variables were analyzed in three separate mixed-design 2 x 3 (maturation level x landing sequence) repeated measures multivariate analysis of variance. RESULTS: Statistical analyses indicated significant maturation level x landing sequence interactions for postpubescent participants who exhibited reduced knee flexion (4.5 degrees ) at initial contact, increased mediolateral knee joint forces [prepubescent: -0.63 +/- 0.21 N.(kg. radicalLH)(-1), postpubescent: 0.55 +/- 0.21 N.(kg. radicalLH)(-1)], and reduced knee extensor moments [prepubescent: -0.0124 +/- 0.001 N.m.(kg.BH. radicalLH)(-1), postpubescent: -0.0079 +/- 0.001 N.m.(kg.BH. radicalLH)(-1)] compared with their prepubescent counterparts. CONCLUSION: These findings suggest that developmental changes influence knee mechanics during landings in female athletes and highlight the need to examine multiple landing patterns when investigating landing strategies.

Initiation of movement from quiet stance: comparison of gait and stepping in elderly subjects of different levels of functional ability.

This study describes how elderly subjects initiate gait, and step from a position of quiet stance. Based on scores from selected standardized tests subjects were placed in either a high (HFL) or low functional level (LFL) group and were asked to initiate gait, step onto a 10 cm high, 1.22 m wide curb and step over a 10 cm high, 9 cm wide obstacle at a self paced speed. Stepping conditions affected the velocity of movement. It was clear that all subjects decreased initiation velocity for both curb and obstacle compared to gait initiation. Swing and stance limb acceleration ground reaction forces and EMG amplitude were modulated according to initiation velocity. Toe clearance was greater for obstacle than curb and gait initiation. Swing toe-off was significantly earlier and there was a trend for obstacle clearance to be greater for the HFL group. Those in the LFL group appear to be at a greater risk for falling due to the possible effect of slower rate of toe-off that could influence toe clearance over the obstacle.

Plantar feedback contributes to the regulation of leg stiffness.

BACKGROUND: Running and hopping involve moving in a bouncing fashion during which the limbs behave as springs. The ability to alter the stiffness of these leg springs is essential to maintaining an efficient gait. Since the plantar surface of the foot is the only part of the body to encounter the ground during bipedal locomotion, it would seem logical that some aspect of the neurological functioning of the foot is responsible for transmission of information about the surface characteristics to the central nervous system, resulting in changes in leg stiffness. METHODS: Ten subjects (9 males, 1 female) participated in this experiment. Lidocaine was injected inferior and posterior to the lateral malleolus in order to achieve tibial nerve block at the level of the ankle. Subjects hopped at 2.2 Hz on a force plate while data were collected at 1000 Hz. Data were analyzed for peak force and leg stiffness and compared using a repeated measures ANOVA. FINDINGS: Tactile sensation, deep pressure sensation, and abductor hallucis activity displayed significant decreases following the injection, as did postural stability. Subjects demonstrated a significantly decreased leg stiffness after the nerve block (P<.01). INTERPRETATION: Plantar sensation has an effect on regulating leg mechanics in hopping. A loss of sensation in this region can exert a significant impact on the properties of the leg in gait, and future research should determine the specific pathways by which plantar feedback exerts this effect.

Changes in distal muscle timing may contribute to slowness during sit to stand in Parkinsons disease.

OBJECTIVE: To compare patterns of muscle activation in the lower extremity and subsequent forces during sit to stand in persons with Parkinsonism. BACKGROUND: There is an interruption of the tibialis anterior/soleus interaction during forward oriented movements in some subjects with Parkinsonism, including sit to stand. This task is a major determinant of independence and 44% of those with Parkinsonism report difficulty. METHODS: 41 subjects with Parkinsonism were asked to stand up from a bench. Peak acceleration and vertical ground reaction forces, the slopes to these peaks, and the timing of events were measured. Surface electrodes were placed on tibialis anterior and soleus. RESULTS: The slower group produced force at slower rate than the fast group. The slower group spent 64% of the time taken to stand to complete the flexion-momentum phase, and the fast group spent 56%. The slower group had a larger proportion of co-contraction trials than the other groups. CONCLUSIONS: Slower subjects took longer to perform the task due to a longer time for seat off. Deficits recruiting tibialis anterior may contribute to the decreased rate of production of the acceleration forces and the longer time required for seat off. Relevance Decreased rate of rise of force is used to identify fallers in the elderly and subjects with stroke. Decreased rates of force production may therefore assist in identifying those with Parkinsonism at risk of falls. Treatment strategies designed to facilitate tibialis anterior activation may improve the functional performance of this task.

Temporo-spatial gait parameters during street crossing conditions: a comparison between younger and older adults.

Most traffic accidents involving pedestrians happen during street crossing. Safe street crossing by older adults requires complex planning and imposes high cognitive demands. Understanding how street crossing situations affect younger and older adults' gait is important to create evidence-based policies, education and training. The objective of this study was to develop and test a method to evaluate temporo-spatial gait parameters of younger and older adults during simulated street crossing situations. Twenty-two younger (25±2 years old) and 22 older adults (73±6 years old) who lived independently in the community completed 3 walking trials at preferred gait speed and during simulated street crossing with regular and with reduced time. There were significant differences between groups (p<0.001) and conditions (p<0.001). Older adults' street crossing walking speed was higher than their preferred speed (p<0.001). Gait during simulated street crossing resulted in significant and progressive gait changes. The methods developed and tested can be used to (1) evaluate if people are at risk of falls and accidents during street crossing situations, (2) to compare among different groups, and (3) to help establish appropriate times for older pedestrians to cross streets safely. The current time to cross streets is too short even for healthy older adults.

Kinesio Taping effects on knee extension force among soccer players.

BACKGROUND: Kinesio Taping (KT) is widely used, however the effects of KT on muscle activation and force are contradictory. OBJECTIVE: To evaluate the effects of KT on knee extension force in soccer players. METHOD: This is a clinical trial study design. Thirty-four subjects performed two maximal isometric voluntary contractions of the lower limbs pre, immediately post, and 24 hours after tape application on the lower limbs. Both lower limbs were taped, using K-Tape and 3M Micropore tape randomly on the right and left thighs of the participants. Isometric knee extension force was measured for dominant side using a strain gauge. The following variables were assessed: peak force, time to peak force, rate of force development until peak force, time to peak rate of force development, and 200 ms pulse. RESULTS: There were no statistically significant differences in the variables assessed between KT and Micropore conditions (F=0.645, p=0.666) or among testing sessions (pre, post, and 24h after) (F=0.528, p=0.868), and there was no statistical significance (F=0.271, p=0.986) for interaction between tape conditions and testing session. CONCLUSION: KT did not affect the force-related measures assessed immediately and 24 hours after the KT application compared with Micropore application, during maximal isometric voluntary knee extension.

Spinal cord modulation associated with isometric contractions.

OBJECTIVE: The dual-strategy hypothesis explains single-joint voluntary movement by dividing movements into two different strategies and suggesting that different excitation pulses modulate these movements. The existence of this excitation pulse was evaluated by quantifying magnitude and timing changes in the H-reflex (changes in spinal excitability) prior to a voluntary contraction. These changes in spinal excitability were assessed during a ballistic plantar flexion isometric contraction, where both the target size and force level was manipulated. METHODS AND MATERIALS: Subjects were seated in a modified chair with a force transducer placed under the metatarsal heads to measure ankle force output. Following a visual stimulus subjects were trained to produce a plantar flexion force of 25% and 50% of a maximum voluntary contraction, within target sizes of 5% and 15% of the selected force level. Soleus motor neuron reflex excitability was analyzed by measuring changes in the H/M ratio. The H-reflex was randomly elicited by tibial nerve stimulations at 15, 30, 45, 60, 75 and 90 ms prior to the recorded average soleus premotor time for each of the force and target size conditions. RESULTS: A two-way repeated-measures analysis of variance indicated a significant effect among target sizes for the time of change in spinal excitability, slope of facilitation (rate of rise of spinal excitability), and peak facilitation. A significant difference was also established between force levels for the slope and peak facilitation, but there was no difference with time of facilitation. CONCLUSIONS: These results indicate that changes in both target size and force level can influence slope and peak of facilitation. However, only target size appears to affect the time of facilitation. Results clearly support the existence of an excitation pulse that is regulated by the type of movement.

Does postural instability affect the initiation of human gait?

During gait initiation (GI), decoupling of the center of mass and center of pressure allows the center of mass to fall forwards. Subjects initiated gait rapidly before and after tibial nerve block of the tibial nerve. Static single limb stability, stance limb ground reaction forces, electromyogram and temporal data were measured. It was hypothesized that postural stability would decrease post-block and that this would affect the kinetic and temporal properties of GI. Subjects had significantly decreased postural stability post-block and changes in normal gait kinetics, however, no changes were noted in ground reaction forces or relative temporal data of the GI task. The finding that GI was unaffected by diminished single leg postural instability suggests that GI is a pre-programmed task.

The interaction between leading and trailing limbs during stopping in humans.

While the initiation of gait has been well studied, the mechanisms of stopping the forward progression of the center of mass have received less attention. The purpose of this current experiment was to examine the effects of constraining cadence on how the body is brought to a stop. Lower limb electromyogram (gluteus medius, hamstrings and soleus (SOL)) and force plate data were compared between two gait conditions, walking and planned stopping, at three different cadences (100, 125 and 150% of normal cadence). As cadence increased, the onset of muscle activity prior to heel-strike decreased for all muscles except SOL. SOL activity was evident prior to heel-strike during stopping and after heel-strike during walking. As cadence increased, onset times before heel-strike were shorter in stopping and SOL became active more rapidly after heel-strike in walking. The normalized duration of muscle activity remained invariant as cadence increased. This activity was always longer under the lead limb during stopping at each cadence. This was reflected by increases in the braking forces produced by the leading limb. The rate at which force was generated was not different between gait conditions but increased with increasing cadence. Thus, subjects relied less on the trailing limb and more on the leading limb as cadence increased.

Sural nerve evoked responses in human hip and ankle muscles while standing.

The objective of this study was to investigate the influence of background EMG, as manipulated by changes in limb loading, and electrical stimulus intensity on sural nerve evoked EMG responses in proximal hip (ipsilateral gluteus medius and contralateral adductor longus) and distal ankle (ipsilateral soleus) muscles during quiet standing. We studied 14 healthy subjects who were instructed to stand on a force platform and load the right leg to 20, 30, 60, and 80% body weight. Trains of stimuli were delivered to the right sural nerve at three different intensities (1.5, 2, and 3 perception threshold). Average evoked responses from each of the three muscles were obtained for each combination of body weight and stimulus intensity. Reflex responses were consistently seen in gluteus medius and soleus but not adductor longus. The responses in gluteus medius and soleus consisted of complex inhibitory and excitatory responses with the primary effect in gluteus medius being a short latency excitation (mean latency of 57 ms) and in soleus, a short latency inhibition-excitation (latencies of 47 and 58 ms, respectively). The amplitudes of the responses were influenced primarily by background EMG. The results demonstrate consistent sural nerve evoked EMG responses in both a hip (gluteus medius) and ankle (soleus) muscle. While the findings for soleus generally corroborate and extend previous studies, the responses observed for the lateral hip muscle have not been previously reported.

Braking impulse and muscle activation during unplanned gait termination in human subjects with parkinsonism.

Persons with parkinsonism (PD) are known to have difficulty with both rapid force production and declination, and may not be able to adjust force levels during bimanual tasks in the upper extremity. We proposed that these deficits might underlie the problems experienced by those with PD when attempting to rapidly terminate locomotor activity. Rapid gait termination requires concomitant increases in braking impulse and decreases in propulsion impulse. We hypothesized that those with PD would be less able to modulate muscle activity and the associated braking impulse during gait termination. Muscular activity of soleus, tibialis anterior and gluteus medius, and braking impulse were compared between a group of subjects with PD and age and gender matched control subjects. Subjects with PD had similar patterns of muscular activation to control subjects although at dramatically reduced levels of amplitude. Consequently, PD subjects were unable to generate sufficient net braking impulse under time-critical conditions.