Minute-by-minute differences in co-activation during treadmill walking in cerebral palsy.

The primary purpose of this study was to determine, in children and adolescents with mild spastic cerebra palsy (CP); 1) minute-by-minute differences in lower limb antagonist muscle co-activation and stride length (SL) during treadmill walking following 12-15 minutes of treadmill walking practice, and 2) if the minute-by-minute pattern of co-activation is affected by site (thigh or lower leg) and lower limb dominance. A secondary purpose was to determine if overall there is a difference in co-activation between the dominant and non-dominant lower limbs. Eight independently ambulatory children and adolescents with mild spastic CP (9.2-15.7 yr) participated in the study. Minute-by-minute lower limb antagonist muscle co-activation and SL were measured during a 3-minute treadmill walk at 90% of individually determined fastest treadmill walking speed. Non-dominant thigh (quadriceps, hamstring muscles) co-activation decreased between minute 1 and a) minute 2 (6%), b) minute 3 (7.2%). Co-activation for the dominant lower leg (tibialis anterior, triceps surae muscles) decreased between minute 1 and minute 3 (11.3%). Non-dominant thigh co-activation was on average 27.3% higher than for the dominant thigh. Thigh co-activation was on average 27.7% higher than for the lower leg, independent of dominance or time. SL increased between minute 1 and minute 3 by 2.1%. Twelve to 15 minutes of treadmill walking practice may be sufficient time to obtain stable co-activation and SL values by minute 2 of a fast treadmill walk. Dominance and site affect the magnitude of co-activation.

Enhancing the ability of gait analyses to differentiate between groups: scaling gait data to body size.

One goal of gait analysis is to distinguish clearly between a set of abnormal gait values measured from a patient referenced to a comparable population. However, the comparable population is often composed of individuals of various heights and weights, which increases inter-subject gait value variation which reduces the ability of a statistical test to identify a set of gait data outcomes with evaluative properties. Therefore, scaling gait data, based on subject leg length and mass, is commonly used to decrease the inter-subject variation but the efficacy of these methods is unknown. In this paper each of eight scaling strategies (none, ad hoc, dimensionless numbers, and five connected strategies based on similarity, dimensional analysis and muscle properties) were used to modify a set of gait data outcomes acquired from 10 individuals spanning a wide range of height (1.33-1.96 m) and mass (42.3-148.8 kg). These data were then examined to select that strategy and those scaling factors which maximally reduced inter-subject variation. The ad hoc, dimensionless numbers, and dynamic/mechanical/elastic (diameter of a limb (D) proportional to it's length (L) to the 1.5 power; time proportional to L(2) D(-1)) scaling strategies reduced the global inter-subject gait data outcome variation to 44% of its un-scaled value. Considering ten commonly reported gait data outcomes (temporal and spatial (stride time, stride length, progression velocity), kinematic (angles in the sagittal and frontal planes, angles in the transverse plane), external kinetic (ground reaction force and moment), and internal kinetic (joint force, moment, and power)) these three scaling strategies provided the largest number of minimum inter-subject variations (10, 10, and 9, respectively). Reduced inter-subject variation in gait data outcomes increases the ability of a statistical tool to detect a difference between a patient and a comparable group. With a statistically significant difference a clinician can then decide if this patient's gait pattern clinically deviates from that of the comparable group and an appropriate intervention warranted. The ad hoc, dimensionless numbers, and the dynamic/mechanical/elastic scaling strategies all reduce maximally the inter-subject variation in gait data outcomes.

Effect of patient position on the consistency of placing the rearfoot at subtalar neutral.

The ability of foot care specialists to place a rearfoot at the subtalar neutral position is important for the care of patients who require foot orthosis prescription, fabrication, and management. Although some clinicians perform this procedure with the patient in the prone position, others prefer a seated or standing approach. This study examined whether patient position and preferred patient position influence the ability of clinicians to place a subject's rearfoot at the subtalar neutral position. The results suggest the following: a clinician's ability to find the subtalar neutral position is better with a seated subject; clinicians do not necessarily perform better assessments on a subject in a position corresponding to their patient position preference; and clinicians who prefer their patients prone generally have more flexible and reproducible observations. In addition, the findings suggest that the nature and relative importance of the tactile and visual cues used by clinicians to place a rearfoot at the subtalar neutral position warrant further exploration.

Classification of errors in locating a rigid body.

This paper discusses the manner in which random Gaussian errors affect the determination of body segment kinematics. For the process of modelling rigid body (RB) motion, three types of kinematic errors, input, measured and theoretical, are identified. These correspond to errors in: the determination of three-dimensional observed points, the RB fit of those points, and the estimation of true RB positions, respectively. Of these, the theoretical error is most critical and most pivotal. Accuracy is provided when the theoretical error is minimised, yet only the measured error can be minimised by RB modelling algorithms. In computer simulations one may determine the effect that such manipulations have on theoretical error, yet in most experimental conditions this value may not even be calculated. Fortunately, computer simulations can be performed to determine the inter-relationships between types of RB modelling errors. Such simulations can also be used to investigate the effects of RB shape. In this paper, Monte Carlo simulations were performed on three unit radius RBs; a triangle, a square and a tetrahedron. Although the use of the triangle provided the lowest measured error, this also coincided with the greatest theoretical error. The use of redundant points was found to yield superior theoretical accuracies. A slight advantage was gained with use of the non-planar point arrangement on the tetrahedron, both the measured and theoretical errors were reduced. Finally, the superiority of RB modelling over individual point tracking was reflected in all of the results; between 33 and 50% of the input error was eliminated with the use of RB modelling.

Rear foot inversion/eversion during gait relative to the subtalar joint neutral position.

Clinicians often fabricate foot orthotic devices at the subtalar joint neutral position (STNP) to mimic the position of the rear foot during midstance. However, rear foot motion during gait, relative to the resting standing foot position, not the STNP, is often reported in the literature. The motion of the rear foot relative to a valid estimate of the STNP is unknown. In this study, six experienced foot care specialists manually placed the rear part of the feet of nine subjects at the STNP seven or eight times to obtain a valid estimate of each subject's STNP. The worst-case mean and 95% confidence interval of the STNP estimate for any one subject was 0.0 degree +/- 0.7 degree. These nine subjects then walked on a motor-driven treadmill, set at 0.89 meters/sec, and three-dimensional estimates of each subject's rear foot inversion/eversion motion were obtained, then averaged over 6 to 26 strides. For most subjects, the rear foot was always everted during stance with mean and standard deviation maximal eversion (7.2 degrees +/- 1.2 degrees) occurring at 44% of the total gait cycle. The inversion/eversion orientation during swing was characterized by 1 degree to 2 degrees of eversion, with a small amount of inversion in early swing. These findings have implications for the fabrication of foot orthoses, since the rear foot is rarely near the STNP during stance.

Proficiency of foot care specialists to place the rearfoot at subtalar neutral.

The proficiency of clinicians to place a rearfoot at the subtalar neutral position is important for the treatment of patients with lower extremity dysfunctions, and especially for foot orthosis prescription, fabrication, and management. However, the ability of experienced foot care specialists to perform this task has not been statistically compared with an average capacity. In this study, eight experienced chiropodists and eight untrained physiotherapy students placed six rearfeet at the subtalar neutral position five times. Statistically, the foot care specialists were able to find the subtalar neutral position better than the students (mean 0.00 versus 0.99 degrees, SD 1.84 versus 2.97 degrees, range -5.27 degrees to 4.33 degrees versus -6.25 degrees to 9.27 degrees). This can be interpreted as stating that foot care specialists and untrained students place a rearfoot within +/- 1 degree of the subtalar neutral position 41.3% and 25.0% of the time, respectively. Corresponding values within +/- 2 degrees of the subtalar neutral position are 72.3 degrees and 47.6 degrees, respectively. Alternatively, it can be stated that experienced foot care specialists are within +/- 3.0 degrees of the subtalar neutral position 90% of the time. A corresponding value for the students is +/- 4.9 degrees. These results suggest that although experienced foot care specialists position a rearfoot at the subtalar neutral position better than untrained physiotherapy students, there is room for improvement.

The effect of soft foot orthotics on three-dimensional lower-limb kinematics during walking and running.

BACKGROUND AND PURPOSE: Although foot orthotics are often prescribed to alter the lower-extremity mechanics during the stance period of gait, there is little documentation of the actual effect of foot orthotics on the movement of the lower-extremity joints during walking and running. This study examined the effect of foot orthotics on the range of motion of the talocrural/subtalar joint and the knee joint in three dimensions during walking and running. SUBJECTS: Ten female adolescent subjects, aged 13 to 17 years (X = 14.4, SD = 1.1) who were diagnosed with patellofemoral pain syndrome and exhibited forefoot varus greater than 6 degrees and/or calcaneal valgus greater than 6 degrees participated in the study. METHODS: Thirty strides of walking and running on a treadmill were recorded for each of the orthotic and nonorthotic conditions for each subject using an optoelectronic recording technique. Analyses of variance for repeated measures were performed on the range of motion of the talocrural/subtalar joint and knee joint for each plane of motion (ie, six separate analyses). The main factors of each analysis were the effect of the orthotic (orthotic condition versus nonorthotic condition), mode of ambulation (walking and running), and phase of the stance period (contact, mid-stance, and propulsion). RESULTS: No differences were found in sagittal-plane movements. Reductions of 1 to 3 degrees occurred with orthotic use for the talocrural/subtalar joint during walking and running in the frontal and transverse planes. The orthotics reduced knee motion in the frontal plane during the contact and mid-stance phases of walking, but increased the motion during the contact and mid-stance phases of running. CONCLUSIONS AND DISCUSSION: This study shows that corrections to the static position of forefoot varus and calcaneal valgus can result in changes in transverse- and frontal-plane motion of the foot and knee during walking and running.

Evaluation of soft foot orthotics in the treatment of patellofemoral pain syndrome.

BACKGROUND AND PURPOSE: The effectiveness of soft foot orthotics in the treatment of patients who have patellofemoral pain syndrome was investigated. SUBJECTS: Subjects were 20 adolescent female patients, aged 13 to 17 years (mean = 14.8, SD = 1.2), who were diagnosed with patellofemoral pain syndrome and who exhibited excessive forefoot varus or calcaneal valgus. METHODS: Subjects were randomly assigned to one of two groups: a control group (n = 10), which took part in an exercise program, or a treatment group (n = 10), which used soft foot orthotics in addition to participating in the exercise program. The exercise program consisted of quadriceps femoris and hamstring muscle strengthening and stretching exercises. A visual analogue scale was used to assess the level of pain of the subjects over an 8-week period. RESULTS: Both the treatment and control groups demonstrated a significant decrease in the level of pain, but the improvement of the treatment group was significantly greater than that of the control group. CONCLUSION AND DISCUSSION: The results suggest that in addition to an exercise program, the use of soft foot orthotics is an effective means of treatment for the patient with patellofemoral pain syndrome.

The role of the contralateral limb in below-knee amputee gait.

Very little quantitative biomechanical research has been carried out evaluating issues relevant to prosthetic management. The literature available suggests that amputees may demonstrate an asymmetrical gait pattern. Furthermore, studies suggest that the forces occurring during amputee gait may be unequally distributed between the contralateral and prosthetic lower limbs. This study investigates the role of the contralateral limb in amputee gait by determining lower limb joint reaction forces and symmetry of motion in an amputee and non-amputee population. Seven adult below-knee amputees and four non-amputees participated in the study. Testing involved collection of kinematic coordinate data employing a WATSMART video system and ground reaction force data using a Kistler force plate. The degree of lower limb symmetry was determined using bilateral angle-angle diagrams and a chain encoding technique. Ankle, knee and hip joint reaction forces were estimated in order to evaluate the forces acting across the joints of the amputee's contralateral limb. The amputees demonstrated a lesser degree of lower limb symmetry than the non-amputees. This asymmetrical movement was attributed to the inherent variability of the actions of the prosthetic lower limb. The forces acting across the joints of the contralateral limb were not significantly higher than that of the non-amputee. This suggests that, providing the adult amputee has a good prosthetic fit, there will not be increased forces across the joints of the contralateral limb and consequently no predisposition for the long-term wearer to develop premature degenerative arthritis.

Effect of load, cadence, and fatigue on tibio-femoral joint force during a half squat.

Ten male university student volunteers were selected to investigate the 3D articular force at the tibio-femoral joint during a half squat exercise, as affected by cadence, different barbell loads, and fatigue. Each subject was required to perform a half squat exercise with a barbell weight centered across the shoulders at two different cadences (1 and 2 s intervals) and three different loads (15, 22 and 30% of the one repetition maximum). Fifty repetitions at each experimental condition were recorded with an active optoelectronic kinematic data capture system (WATSMART) and a force plate (Kistler). Processing the data involved a photogrammetric technique to obtain subject tailored anthropometric data. The findings of this study were: 1) the maximal antero-posterior shear and compressive force consistently occurred at the lowest position of the weight, and the forces were very symmetrically disposed on either side of this halfway point; 2) the medio-lateral shear forces were small over the squat cycle with few peaks and troughs; 3) cadence increased the antero-posterior shear (50%) and the compressive forces (28%); 4) as a subject fatigues, load had a significant effect on the antero-posterior shear force; 5) fatigue increased all articular force components but it did not manifest itself until about halfway through the 50 repetitions of the exercise; 6) the antero-posterior shear force was most affected by fatigue; 7) cadence had a significant effect on fatigue for the medio-lateral shear and compressive forces.

Effects of downhill or uphill training prior to a downhill run.

Nine men volunteered to undergo 10% downhill (DT) or 10% uphill (UT) treadmill training at 60% VO2max for 12 minutes on two consecutive days. Four days later the downhill run (DR) was repeated. All subjects reported considerable muscular soreness following DT but not UT. When DR followed UT muscular soreness was again reported but not when DR followed DT. Peak knee flexion and extension moment of force data at five angular velocities, ranging from 0.52-4.71 rad s-1, were reduced following DR regardless of whether soreness was present. During each run VO2 was stable during UT but drifted upwards during DT and DR. This increase in VO2 was not due to changes in the stride frequency since the stride frequency remained nearly constant on all days except for the second day of the DT when an increase of 20 strides per minute occurred; this was the only day the subjects ran while sore. It was concluded that two 12 minute bouts of downhill running were sufficient to protect against the occurrence of muscular soreness in subsequent downhill run. However, this training was insufficient to prevent a 2-3 day loss of muscular strength. These results support the hypothesis that the sensation of delayed onset muscle soreness and the temporary strength loss associated with eccentric contraction have different physiological causes.

Puck impact response of ice hockey face masks.

A sample of new ice hockey face masks was struck over the nose or eye of a headform by pucks shot at velocities of 11-39 m/s (25-87 m.p.h.). Deformation of the masks was studied from high speed film. Acceleration pulses transmitted to the center of gravity of the headform were recorded. Peak accelerations never exceeded 86 G's and were well below reported concussion thresholds (200 G's). The film showed contact of the mask or puck with the face at puck velocities of 28 m/s (60 m.p.h.) and above. These results indicate a somewhat lower "safe" puck impact velocity (28 m/s) than that stated by the Canadian Standards Association (32 m/s) under the standard which applied to these masks. Some boys 12 years and older can shoot pucks at 28 m/s (60 m.p.h.). We urge that all manufacturers of sports protective equipment incorporate state of the science, quantitative evaluations of their products, beyond minimum CSA standard testing, in their design programs to improve the quality of information transmitted to the public.

Aircrew helmet protection against potential cerebral concussion in low-magnitude impacts.

The response of the Gentex DH-151 (contact type) and Gentex 411 (suspension type) aircrew helmets to low-magnitude impacts, such as those sometimes encountered during cockpit buffeting, in ejection, and in parachute landings, was studied to augment the data base on helmet performance. The helmets, mounted on a Hodgson headform, were dropped on the crown and rear at impact velocities up to 4.97 m/s. Acceleration time histories were tape recorded and digitized and Gadd Severity Indices (GSI), among others, were calculated from the resultant acceleration curve. Both helmets kept the GSI below predicted concussion thresholds at 4.97 m/s and were considered to perform well on initial impacts. On second impacts, the GSI rose considerably because the shell and liner of the DH-151 cracked and the suspension of the "141" stretched during the first blow. Improvement of the multiple impact performance of both helmets appears desirable, although the suspension helmet performed slightly better than the contact helmet with respect to the criterion used.