Viviana Rota

Gait analysis on split-belt force treadmills: Validation of an instrument

Tesio L, Rota V: Gait analysis on split-belt force treadmills: validation of an instrument. Am J Phys Med Rehabil 2008;87:515–526. Objective:Gait analysis (GA) is usually performed during overground walking, with ground reactions being recorded through force platforms embedded in the floor. Body kinematics and surface electromyography (EMG) are also recorded. GA on treadmills resting on force sensors (GAFT) is rather uncommon and has been criticized on various grounds (less reliability of force records; biomechanical differences in walking kinematics and dynamics). On the other hand, the treadmill allows very fast recording of data from many successive strides, at known and constant average speeds. The goals of this study were (a) to validate a system for GAFT based on a commercially available “split-belt” force treadmill, (b) to provide evidence that data can be compared with established norms from overground GA, and (c) to lend support to the potential clinical validity of the GAFT approach. Design:The treadmill adopted here allows subjects to walk on two parallel independent treadmills. Each of them is mounted on four 3D force sensors. Eight healthy adults (four women; ages 22–35 yrs) were tested on the treadmill, each at the average walking speed he or she adopted overground (average across subjects: 1.35 ± 0.05 m·sec−1). Ground reactions, hip, knee, and ankle sagittal rotations, torques, power, and surface EMG from four thigh and leg muscles were recorded simultaneously. Results:Results were compared with those relating to a sample of 40 healthy adults (20 women; manufacturers data, replicating published data) walking on floor-embedded force platforms (age 20–40 yrs; speed 1.33 ± 0.06 m·sec−1). An 8% shorter stride length was adopted on the treadmill. All of the other results matched those obtainable overground. Conclusions:The results suggest that GAFT performed on the tested treadmill is a promising method of GA in a clinical setting.

Walk Ratio (Step Length/Cadence) as a Summary Index of Neuromotor Control of Gait: Application to Multiple Sclerosis.

In healthy adults, the step length/cadence ratio [walk ratio (WR) in mm/(steps/min) and normalized for height] is known to be constant around 6.5 mm/(step/min). It is a speed-independent index of the overall neuromotor gait control, in as much as it reflects energy expenditure, balance, between-step variability, and attentional demand. The speed independence of the WR in patients with multiple sclerosis (MS), and its capacity to discriminate (a) across patients with MS and controls and (b) among disability levels in MS were tested. The WR was computed in 30 outpatients with MS [20 women, 10 men; Extended Disability Status Scale (potential range: 0–10, observed median 3.5, range 2.5–5.0)] walking at free speed (range: 0.43–1.67 ms−1), and in 30 healthy controls (20 women, 10 men) at free and slow speed (range: 0.55–1.67 ms−1). The WR was 6.38±0.66 in controls versus 5.36±0.86 in patients with MS (P<0.000), independent of age, sex, and walking speed. The WR was 5.95±0.69 and 4.90±0.70 in patients with an Extended Disability Status Scale score (P<0.001) below or above the median, respectively, independent of the disease duration (P<0.000). In patients with MS, the WR is a disability-sensitive index of neuromotor control of gait, and thus a promising outcome measure for treatments aimed at improving motor coordination.

Anticipatory postural adjustments in arm muscles associated with movements of the contralateral limb and their possible role in interlimb coordination

While sitting on a turnable stool, with both shoulders flexed at 90° or, alternatively, with arms parallel to the trunk and the elbows flexed at 90°—the hands being semisupine—subjects performed unidirectional and cyclic movements on the horizontal plane of the right arm (adduction–abduction) or hand (flexion–extension). The left arm was still, in a position symmetrical to that of the right limb and with the hand contacting a fixed support by the palmar or dorsal surface. During both unidirectional and cyclic arm or hand movements, activation of the prime mover muscles (right Pectoralis Major for arm adduction and Infraspinatus for abduction; right Flexor Carpi Radialis and Extensor Carpi Radialis for the hand movements) was accompanied by activation of the homologous muscles of the contralateral arm and inhibition of antagonists. The contralateral activities (1) regularly preceded the burst in the movement prime movers and (2) were organised in fixation chains that, exerting forces on the hand fixed support, will counterbalance the rotatory action exerted on the trunk by the primary movement. Based on these features, these activities may be classified as anticipatory postural adjustments (APAs). The observed APAs distribution is such as to favour the preferential (mirror symmetrical) coupling of upper limb movements on the horizontal plane. The possible role of these APAs in determining the different constraints experienced when performing mirror symmetrical versus isodirectional coupling is discussed.

Postural adjustments in arm and leg muscles associated with isodirectional and antidirectional coupling of upper limb movements in the horizontal plane

The hypothesis that anticipatory postural adjustments (APAs) may concur in generating the directional preference experienced during limb coupled movements was tested by measuring the electromyographic and mechanic postural actions elicited when moving: (1) one single arm/hand and, (2) both limbs, iso- or antidirectionally coupled. During fast adduction of the right arm in the horizontal plane (prime mover, pectoralis Major, rPM) APAs were recorded in the contralateral lPM as well as in the right ischiocruralis (rIC) muscle. This last action was associated to a transient increase of Tz (torque around body vertical axis) in the direction opposite to arm rotation. Both the APAs in rIC and the Tz changes nearly doubled in size when arms were coupled isodirectionally (adduction of one arm and abduction on the other) while they vanished when both arms were simultaneously adducted (antidirectional coupling). Conformably, during rhythmic arm oscillations APAs and Tz were cyclically modulated when movements were isodirectional, the modulation amplitude being strongly enhanced by increasing the movement frequency. When oscillations were antidirectional neither APAs nor Tz changes were observed, even if frequency was incremented. The postural actions linked to unidirectional or cyclic movements of the hand were affected by either coupling or frequency in the same way as arm movements, albeit much smaller in size. In conclusion, during antidirectional movements APAs in prime movers are synergic with voluntary activation and no postural engagement is requested to leg muscles. Conversely, during isodirectional movements, APAs in prime movers conflict with the voluntary commands and a strong, frequency-dependent, postural effort is required to leg muscles. How these factors may co-operate in determining the preference for antidirectional coupling is discussed.

Knee rotationplasty: motion of the body centre of mass during walking

Knee rotationplasty (KRP) is a type of surgery in which the rotated ankle serves as a new knee after being removed for bone tumor. Although this limb salvage surgery is rarely indicated in properly selected patients, it may offer functional advantages over transfemoral amputation, and more durable results compared with a prosthesis. The walking mechanics of adult patients after KRP is believed to be close to that of below-knee amputees. In this study, we evaluated steady-state walking of KRP patients from the viewpoint of the overall muscle power needed to keep the body centre of mass in motion. Three adult patients after KRP, all athletes, were evaluated. Ground reactions during walking were recorded during six subsequent strides on a force treadmill. The positive mechanical work and power sustaining the motion of the centre of mass and the recovery of muscle energy due to the pendulum-like mechanism of walking were computed and compared with those obtained in previous studies from above-knee, below-knee amputees and healthy individuals. In KRP patients, walking was sustained by a muscle power output which was 1.4–3.6 times lower during the step performed on the rotated limb than on the subsequent step. The recovery of muscle energy was slightly lower (0.9) or higher (1.3–1.4 times) on the affected side. In two out of the three KRP patients, our findings were more similar to those from above-knee amputees than to those from below-knee amputees. After KRP, the rotated limb does not necessarily provide the same power provided by below-knee amputation. This may have a relevance for the paralympic classification of KRP athletes.

Bimanual dexterity assessment: Validation of a revised form of the turning subtest from the Minnesota dexterity test

Bimanual coordination underlies many daily activities. It is tested by various versions of the old Minnesota Dexterity Test (dating back to 1931, ‘turning’ subtest). This, however, is ill standardized, may be time-consuming, and has poor normative data. A timed-revised form of the turning subtest (MTTrf) is presented. Age-related norms and test–retest reliability were computed. Sixty-four healthy individuals, 24–79 years, comprising 34 women, were required to pick up 60 small plastic disks from wells, rotate each disk, and transfer it to the other hand, which must replace it, as quickly as possible. Two trials were requested for each hand (ABBA sequence). The average time (seconds) across the 4 trials gave the test score. Participants were grouped (CART algorithm) into 3 statistically distinct (P<0.05) age×score strata, with cutoff 53+ and 73+ years, and tested at baseline and after 1 week. Test–retest reliability was measured both as consistency [intraclass correlation coefficient (ICCs) model 2.1] and as agreement (Bland–Altman plot). From the ICCs, the individual test–retest minimal real difference (in seconds) was computed. The whole MTTrf took less than 4 min to administer. Baseline scores ranged from 40 to 78 s. The ICCs ranged from 0.45 to 0.81 and the minimal real difference ranged from 6.68 to 13.40 s across the age groups. Fifty-nine out of 64 observations (92%) fell within the confidence limits of the Bland–Altman plot. The MTTrf is a reliable and practical test of bimanual coordination. It may be a useful addition to protocols of manual testing in occupational therapy.

Surgical leg rotation: cortical neuroplasticity assessed through brain mapping using transcranial magnetic stimulation

Rotationplasty (Borggreve-Van Nes operation) is a rare limb salvage procedure, most often applied to children presenting with sarcoma of the distal femur. In type A1 operation, the distal thigh is removed and the proximal tibia is axially rotated by 180°, remodeled, grafted onto the femoral stump, and then prosthetized. The neurovascular bundle is spared. The rotated ankle then works as a knee. The foot plantar and dorsal flexors act as knee extensors and flexors, respectively. Functional results may be excellent. Cortical neuroplasticity was studied in three men (30–31 years) who were operated on the left lower limb at ages between 7 and 11 years and were fully autonomous with a custom-made prosthesis, as well as in three age–sex matched controls. The scalp stimulation coordinates, matching the patients’ brain MRI spots, were digitized through a ‘neuronavigation’ optoelectronic system, in order to guide the transcranial magnetic stimulation coil, thus ensuring spatial precision during the procedure. Through transcranial magnetic stimulation driven by neuronavigation, the cortical representations of the contralateral soleus and vastus medialis muscles were studied in terms of amplitude of motor evoked potentials (MEPs) and centering and width of the cortical areas from which the potentials could be evoked. Map centering on either hemisphere did not differ substantially across muscles and participants. In the operated patients, MEP amplitudes, the area from which MEPs could be evoked, and their product (volume) were larger for the muscles of the unaffected side compared with both the rotated soleus muscle (average effect size 0.75) and the muscles of healthy controls (average effect size 0.89). In controls, right–left differences showed an effect size of 0.38. In no case did the comparisons reach statistical significance (P>0.25). Nevertheless, the results seem consistent with cortical plasticity reflecting strengthening of the unaffected leg and a combination of cross-education and skill training of the rotated leg.

Crouch gait can be an effective form of forced-use/no constraint exercise for the paretic lower limb in stroke

In hemiplegic gait the paretic lower limb provides less muscle power and shows a briefer stance compared with the unaffected limb. Yet, a longer stance and a higher power can be obtained from the paretic lower limb if gait speed is increased. This supports the existence of a ‘learned non-use’ phenomenon, similar to that underlying some asymmetric impairments of the motion of the eyes and of the upper limbs. Crouch gait (CG) (bent-hip bent-knee, about 30° minimum knee flexion) might be an effective form of ‘forced-use’ treatment of the paretic lower limb. It is not known whether it also stimulates a more symmetric muscle power output. Gait analysis on a force treadmill was carried out in 12 healthy adults and seven hemiplegic patients (1–127 months after stroke, median: 1.6). Speed was imposed at 0.3 m/s. Step length and single and double stance times, sagittal joint rotations, peak positive power, and work in extension of the hip, knee, and ankle (plantar flexion), and surface electromyography (sEMG) area from extensor muscles during the generation of power were measured on either side during both erect and crouch walking. Significance was set at P less than 0.05; corrections for multiplicity were applied. Patients, compared with healthy controls, adopted in both gait modalities and on both sides a shorter step length (61–84%) as well as a shorter stance (76–90%) and swing (63–83%) time. As a rule, they also provided a higher muscular work (median: 137%, range: 77–250%) paralleled by a greater sEMG area (median: 174%, range: 75–185%). In erect gait, the generation of peak extensor power across hip, knee, and ankle joints was in general lower (83–90%) from the paretic limb and higher (98–165%) from the unaffected limb compared with control values. In CG, peak power generation across the three lower limb joints was invariably higher in hemiparetic patients: 107–177% from the paretic limb and 114–231% from the unaffected limb. When gait shifted from erect to crouch, only for hemiplegic patients, at the hip, the paretic/unaffected ratio increased significantly. For peak power, work, sEMG area, and joint rotation, the paretic/unaffected ratio increased from 55 to 85%, 56 to 72%, 68 to 91%, and 67 to 93%, respectively. CG appears to be an effective form of forced-use exercise eliciting more power and work from the paretic lower limb muscles sustained by a greater neural drive. It also seems effective in forcing a more symmetric power and work from the hip extensor muscles, but neither from the knee nor the ankle.

Gait analysis on force treadmill in children: comparison with results from ground-based force platforms

Gait analysis (GA) typically includes surface electromyographic (sEMG) recording from several lower limb muscles, optoelectronic measurement of joint rotations, and force recordings from ground-based platforms. From the latter two variables, the muscle power acting on the lower limb joints can be estimated. Recently, gait analysis on a split-belt force treadmill (GAFT) was validated for the study of adult walking. It showed high reliability of spatiotemporal, kinematic, dynamic, and sEMG parameters, matching those obtainable with GA on the basis of ground walking. GAFT, however, still needs validation in children. Potential differences with respect to adult GAFT relate to (a) possible high signal-to-noise ratio, given the lower forces applied; (b) higher differences between treadmill and over-ground walking; and (c) limited compliance with the experimental setup. This study aims at investigating whether GAFT provides results comparable with those obtainable from ground walking in children and consistent with results from GAFT in adults. GAFT was applied to three groups of healthy children aged 5–6 years (n=6), 7–8 years (n=6), and 9–13 years (n=8) walking at the same average speed spontaneously adopted overground. The results were compared with those obtained from another study applying GA to an age-matched and speed-matched sample of 47 children, and with those obtained from GAFT in adults. The reliability (as indicated by the SD) of both spatiotemporal and dynamic parameters was higher in GAFT compared with GA. In the 5–6-, 7–8-, and 9–13-year-old groups, at average speeds of 0.83, 1.08, and 1.08 m/s, step length was shorter by 9.19, 3.57, and 2.30% compared with GA in controls at comparable speeds, respectively. For the youngest group, a lower power generation from the plantar flexors (peak power: 1.35±0.32 vs. 2.11±1.02 W/kg) and a slightly more flexed posture of the hip, knee, and ankle joints were observed during GAFT compared with GA in controls. The other gait parameters were very similar between the GAFT and the GA groups. The shortening of step length during GAFT, relative to GA at superimposable speed, was on average of all children 6.8%, in line with the 8% decrease found in adults. The profiles of sEMG and joint rotations, and all of the weight-standardized joint power parameters, matched those recorded in adults. The entire experimental session lasted about 1 h. All children complied with the experimental setting and easily completed the requested tests. In conclusion, GAFT seems to be a promising alternative to conventional GA in children.