Between-day reliability of centre of pressure measures for balance assessment in hemiplegic stroke patients.

BACKGROUND: Stroke patients have impaired postural balance that increases the risk of falls and impairs their mobility. Assessment of postural balance is commonly carried out by recording centre of pressure (CoP) displacements, but the lack of data concerning reliability of these measures compromises their interpretation. The purpose of this study was to investigate the between-day reliability of six CoP-based variables, in order to provide i) reliability data for monitoring postural sway and weight-bearing asymmetry of stroke patients in clinical practice and ii) consistent assessment method of measurement error for applications in physical medicine and rehabilitation. METHODS: Postural balance of 20 stroke patients was assessed in quiet standing on a force platform, in two sessions, 7 days apart. Six CoP-based variables were collected in eyes open and eyes closed conditions: postural sway was assessed with mean and standart deviation of CoP-velocity, CoP-velocity along the mediolateral and anteroposterior axes, and confidence ellipse area (CE(AREA)); weight-bearing asymmetry was assessed with mean CoP position along the mediolateral axis (CoP(ML)). The intraclass correlation coefficient (ICC) was used to determine the level of agreement between test-retest. Small real difference (SRD), corresponding to the smallest change that indicates a real improvement for a single individual, was used to determine the extent of measurement error. RESULTS: ICCs were satisfactory (>0.9) for all CoP-based variables, except for CE(AREA) in eyes open condition and CoP(ML) (<0.8). The SRDs (eyes open/closed conditions) were: 6.1/9.5 mm.s(-1) for mean velocity; 12.3/12.2 mm.s(-1) for standard deviation of CoP-velocity; 3.6/5.5 mm.s(-1) and 4.9/7.3 mm.s(-1) for CoP-velocity in mediolateral and anteroposterior axes, respectively; 17.4/21.4 mm for CoP(ML). Because CE(AREA) showed heteroscedasticity of measurement error distribution, SRD (eyes open/closed conditions) was expressed as a percentage (121/75%) and a ratio (3.68/2.16) obtained after log-antilog procedure. CONCLUSIONS: In clinical practice, the CoP-based velocity variables should be prefer to CE(AREA) to assess and monitor postural sway over time in hemiplegic stroke patients. The poor reliability of CoP(ML) compromises its use to assess weight-bearing asymmetry. The procedure we used could be applied in reliability studies concerning other CoP-based variables or other biological variables in the field of physical medicine and rehabilitation.

Effects of knee and ankle muscle fatigue on postural control in the unipedal stance.

The aim of this study was to compare the effects of acute muscle fatigue of the ankle and knee musculature on postural control by immediate measures after performing fatiguing tasks (POST condition). One group of subjects (n = 8) performed a fatiguing task by voluntary contractions of the triceps surae (group TRI) and the other (n = 9) performed a fatiguing task by voluntary contractions of the quadriceps femoris (group QUA). Each muscle group was exercised until the loss of maximal voluntary contraction torque reached 50% (isokinetic dynamometer). Posture was assessed by measuring the centre of foot pressure (COP) with a force platform during a test of unipedal quiet standing posture with eyes closed. Initially (in PRE condition), the mean COP velocity was not significantly different between group TRI and group QUA. In POST condition, the mean COP velocity increased more in group QUA than in group TRI. The postural control was more impaired by knee muscle fatigue than by ankle muscle fatigue.

Posture analysis on young women before and after 60 days of -6 degrees head down bed rest (Wise 2005).

Twenty-four women divided into three groups: control, exercise and nutrition, have been involved in a -6 degrees head down bed rest (HDBR) experiment for 60 days. The objective was to analyse the effects of microgravity on balance function regulation. Group comparisons assessed the efficiency of countermeasures (specific exercises and in particular diet) on the deleterious effects of simulated microgravity. Measurements of orthostatic and dynamic balance were taken 9 and 2 days prior to the experiment, on the first day of getting up, the following day and 4 and 10 days after, under two visual conditions: eyes open and eyes closed. The results confirmed that, as in any other test performed with ordinary subjects, the postural balance performances are better with eyes open than with eyes closed. The static and dynamic postural performances were impaired on the first day of recovery (R0) following HDBR. This impairment lasted up to 4 days after getting up and, afterwards the volunteers recovered their initial performances. The exercise group recovered static postural performances more quickly than the other groups whereas there were no differences in the recovery of the dynamic balance performances.

Effects of fatigue induced by neuromuscular electrical stimulation on postural control.

The aim was to investigate the effects of fatigue induced by electrical stimulation superimposed onto voluntary muscular contractions on postural abilities and strategy (n=8). Two groups of subjects performed a fatiguing of the triceps surae, the first by voluntary muscular contractions (group VOL) and the second (n=8) by electrical stimulation superimposed onto voluntary muscle contractions (group VOL+ES). Balance was measured before and after the completion of both fatiguing tasks, by using a force platform which recorded centre of foot pressure (COP). Spatio-temporal COP parameters were used to evaluate the postural abilities, and a frequency analysis of the COP excursions (Fast Fourier Transform) was performed to estimate the postural strategy (low frequencies mostly account for visuo-vestibular regulation and high frequencies for proprioceptive regulation). In the post-fatigue condition, spatio-temporal COP parameters were not modified in either group. However, the frequency analysis showed that the high frequency band increased more in group VOL than in group VOL+ES. Calf-muscles fatigue did not impair postural control but it generated a change of the contribution of the proprioceptive information (myotatic loops) greater in group VOL than in group VOL+ES. Calf-muscles fatigue induced a modification of the postural strategy that may be exerted more strongly after voluntary muscular contractions than after electrical stimulation superimposed onto voluntary muscular contractions.

Effects of two types of neuromuscular electrical stimulation training on vertical jump performance.

This study examined the effects of different types of neuromuscular electrical stimulation (NMES) programs on vertical jump performance. Twenty seven healthy trained male students in sports-sciences were recruited and randomized into three groups. The control group (C group, n = 8) did not perform NMES training. Two other groups underwent 3 training sessions a week over 5 weeks on the quadriceps femoris muscle [F group (n = 9): stimulation with an 80 Hz current for 15 min for improving muscle strength; E group (n = 10): stimulation with a 25 Hz current for 60 min for improving muscle endurance]. The height of the vertical jump was measured before NMES training (test 1), one week (test 2) and five weeks (test 3) after the end of the programs. The results showed that the height of the vertical jump significantly increased in both the F and E groups between tests 1 and 2 (5 cm and 3 cm respectively). Results of test 3 showed that both groups preserved their gains. A NMES training program destined to improve muscle endurance does not interfere on vertical jump performance. It can even durably enhance it in the same way as a NMES training program destined to improve muscle strength. Thus, to improve muscle endurance without deteriorating muscle power, sportsmen can use electrical stimulation.

Do sensorial manipulations affect subjects differently depending on their postural abilities?

OBJECTIVES: To examine whether sensorial manipulation affects subjects differently according to their postural performance and the strategies used. The literature showed that the level of competition of soccer players influences their postural performance and strategy. METHODS: Eight high-level (HL) professional soccer players and nine regional-level (RL) soccer players were tested (1) in a reference condition and (2) in a manipulated sensorial condition (MAN). The MAN condition consisted of perturbing the proprioceptive and exteroceptive information. For each postural condition, balance was assessed by measuring the centre of foot pressure using a force platform during a test of bipedal standing posture. RESULTS: The postural control was less perturbed in the HL than in the RL players in the two postural conditions. Moreover, the group-condition interaction showed that the postural control was less disturbed in the HL than in the RL players when the sensory information was manipulated. CONCLUSIONS: The HL soccer players probably possessed a better internal model of verticality than the RL players. Subjects who had a better postural control level were less disturbed by sensorial manipulation than the others in postural regulation.

Postural adaptations specific to preferred throwing techniques practiced by competition-level judoists.

The purpose of this study was to analyse the judoists' postural regulation adopted to accommodate their favorite throwing technique (tokui-waza). The tokui-waza is a technique performed in bipodal or monopodal stance. Twenty three judoists aged between 16 and 20 took part in the protocol. All had a minimum regional sportive level. They were separated into two groups: the one performed a tokui-waza in bipodal stance (BS group) and the others performed a tokui-waza in monopodal stance (MS group). The medio/lateral and antero/posterior dynamic balance was evaluated on one-leg and two-leg support with a seesaw platform laid on a force platform. On two-leg support, the BS group judoists were more efficient than the MS group judoists. On the contrary, on one-leg support, the MS group was more efficient than the BS group. The different movements practiced on one or two-leg induce specific postural adaptations in competition-level judoists. Therefore, the present study shows that the different movements practiced in a given sport can induce particular postural adaptations. This phenomenon must therefore also be taken into account in the protocols used for evaluating postural control in sportsmen.

Dynamic balance sensory motor control and symmetrical or asymmetrical equilibrium training.

OBJECTIVE: Determine whether symmetrical or asymmetrical equilibrium training can enhance the proprioceptive input of the left versus right supporting leg (SL) motor control. METHODS: Proprioceptive input was tested using a seesaw platform through a cross-sectional study. The total spectral energy was recorded and divided into 0-2 and 2-20Hz frequency bands. Experts in asymmetrical tasks (soccer players) were compared to experts in symmetrical tasks (dancers, acrobats) and untrained subjects according to pitch versus roll imbalance direction on each SL. RESULTS: Regarding the low frequency band, spectral energy values were lower for experts than for untrained subjects in the roll direction only, whatever the SL (p<0.05). Regarding the high frequency band, spectral energy values were lower for the left SL compared to the right one for soccer players only (p<0.05). Furthermore, soccer players also exhibited lower values than other subjects on the left SL. CONCLUSIONS: Asymmetrical equilibrium training minimizes the proprioceptive input, emphasizing the role of the biomechanical component in postural regulation. SIGNIFICANCE: Testing athletes on a spontaneous unstable platform is a way to accurately discriminate each SL performance for one type of sport training. In sport medicine rehabilitation, injured SL could be detected with this protocol comparing it with healthy SL.

Postural performance and strategy in the unipedal stance of soccer players at different levels of competition.

CONTEXT: Sport training enhances the ability to use somatosensory and otolithic information, which improves postural capabilities. Postural changes are different according to the sport practiced, but few authors have analyzed subjects' postural performances to discriminate the expertise level among highly skilled athletes within a specific discipline. OBJECTIVE: To compare the postural performance and the postural strategy between soccer players at different levels of competition (national and regional). DESIGN: Repeated measures with 1 between-groups factor (level of competition: national or regional) and 1 within-groups factor (vision: eyes open or eyes closed). Dependent variables were center-of-pressure surface area and velocity; total spectral energy; and percentage of low-, medium-, and high-frequency band. SETTING: Sports performance laboratory. PATIENTS OR OTHER PARTICIPANTS: Fifteen national male soccer players (age = 24 +/- 3 years, height = 179 +/- 5 cm, mass = 72 +/- 3 kg) and 15 regional male soccer players (age = 23 +/- 3 years, height = 174 +/- 4 cm, mass = 68 +/- 5 kg) participated in the study. INTERVENTION(S): The subjects performed posturographic tests with eyes open and closed. MAIN OUTCOME MEASURE(S): While subjects performed static and dynamic posturographic tests, we measured the center of foot pressure on a force platform. Spatiotemporal center-of-pressure measurements were used to evaluate the postural performance, and a frequency analysis of the center-of-pressure excursions (fast Fourier transform) was conducted to estimate the postural strategy. RESULTS: Within a laboratory task, national soccer players produced better postural performances than regional players and had a different postural strategy. The national players were more stable than the regional players and used proprioception and vision information differently. CONCLUSIONS: In the test conditions specific to playing soccer, level of playing experience influenced postural control performance measures and strategies.

Electrical stimulation superimposed onto voluntary muscular contraction.

Electrical stimulation (ES) reverses the order of recruitment of motor units (MU) observed with voluntary muscular contraction (VOL) since under ES, large MU are recruited before small MU. The superimposition of ES onto VOL (superimposed technique: application of an electrical stimulus during a voluntary muscle action) can theoretically activate more motor units than VOL performed alone, which can engender an increase of the contraction force. Two superimposed techniques can be used: (i) the twitch interpolation technique (ITT), which consists of interjecting an electrical stimulus onto the muscle nerve; and (ii) the percutaneous superimposed electrical stimulation technique (PST), where the stimulation is applied to the muscle belly. These two superimposed techniques can be used to evaluate the ability to fully activate a muscle. They can thus be employed to distinguish the central or peripheral nature of fatigue after exhausting exercise. In general, whatever the technique employed, the superimposition of ES onto volitional exercise does not recruit more MU than VOL, except with eccentric actions. Nevertheless, the neuromuscular response associated with the use of the superimposed technique (ITT and PST) depends on the parameter of the superimposed current. The sex and the training level of the subjects can also modify the physiological impact of the superimposed technique. Although the motor control differs drastically between training with ES and VOL, the integration of the superimposed technique in training programmes with healthy subjects does not reveal significant benefits compared with programmes performed only with voluntary exercises. Nevertheless, in a therapeutic context, training programmes using ES superimposition compensate volume and muscle strength deficit with more efficiency than programmes using VOL or ES separately.

Short-term effects of electrical stimulation superimposed on muscular voluntary contraction in postural control in elderly women.

Thirty-two women between 62 and 75 years old were randomized into 3 groups. Each group performed a program of 4 sessions a week over 6 weeks. Group SC (n = 11) climbed up and down stairs, group ES (n = 11) practiced electrostimulation, and group SC + ES (n = 10) superimposed the 2 activities simultaneously. Using a force platform and a seesaw platform, static and dynamic balance in eyes-open and eyes-closed conditions were analyzed before and after the programs for each group. After the programs, the results indicated that dynamic balance improved for the 3 groups, but the contribution of visual information in the control of oscillation amplitude was lower in the SC group than in the ES and SC + ES groups. In the SC + ES group, the electrical stimulation interferes with neurophysiologic afference integration in postural control in relation to voluntary movement. Voluntary exercise appears to be more efficient than electrical stimulation and the superimposed techniques to change balancing tactics in the elderly.

Influence of postural regulation in male judokas' direction of falls.

In competitions, judokas tend to have a predominant direction of fall: forwards or backwards. A relationship was hypothesized between the direction of fall and certain parameters of the judokas' postural activities. 20 judokas, 16 to 19 yr. old (17.7 +/- 0.4 yr.), had practised judo for at least seven years. They were separated into two groups. The group of forward fallers (n = 9) and the group of backward fallers (n = 11) performed posturokinetic tests to assess their static and dynamic balance. One parameter assessed through the analysis of postural activities, the average position of anteroposterior dynamic oscillations, was inversely related to the judokas' direction of fall. Postural activities might not play a direct role but perhaps an indirect one in the direction of falls by expert judokas.

A foot-pointing task and spatiotemporal gait parameters during walking in sportsmen.

Unlike many sports, karate imposes pointing to a target with the lower limb. The nature of each sport could influence gait variables of sportsmen. The aim of this study was to examine the pointing accuracy of limb swing and the spatial and temporal parameters of the walking cycle during walking in karate experts (Group K, n=6) compared to accuracy of nonkarate sportsmen (Group S, n = 11). The second aim of this study was to compare the influence of this skill on the spatial and temporal parameters of the walking cycle between the two groups. The analysis was performed with a device composed of a gait analysis system (locometer) coupled to a lighted walkway. This system provides a measurement of the motor skill and the spatial and temporal gait during walking. Analysis for the pointing task indicated no differences between the Karate and the Sportsmen Groups during walking. Moreover, neither the spatial nor temporal characteristics of walking differed between the two groups. Karate does not therefore seem to develop motor programs specific to enhanced performance on this pointing task during walking or alter the walking cycle as compared to some other competitive sports.