MALTAIS, D., O. BAR-OR, M. PIERRYNOWSKI, and V. GALEA. Repeated Treadmill Walks Affect Physiologic Responses in Children with Cerebral Palsy. Med. Sci. Sports Exerc., Vol. 35, No. 10, pp. 1653–1661, 2003.
Purpose: To determine whether physiologic responses during treadmill walking in children with cerebral palsy (CP) are affected by repeated walking bouts on different days, and whether effects are different at different speeds.
Methods: Three girls and five boys (9.2–15.7 yr, 23.3–64.4 kg) with mild CP received 12–15 min of treadmill walking practice and had their fastest walking speed (FWS) determined during an introductory visit. During each of three subsequent visits (day 1, day 2, day 3), subjects walked for 3 min at 60, 75, and 90% FWS. Resting physiologic measures were taken on day 1.
Results: From day 1 to day 3, net ventilation (V̇E), and net heart rate (HR) at 90% FWS decreased by 3.6 L·min−1 and 8 beats·min−1, respectively. There were no differences between day 1 and day 2 or day 1 and day 3 for any other physiologic variable at any speed. Day 3 was less than day 2 for net HR (60% FWS) and, independent of speed, net V̇O2 (per kilogram of body mass and per stride) and net energy expenditure (kJ·min−1). Between-day reliability (R) of physiologic responses was ≥ 0.95, except respiratory rate (R = 0.75). Intrasubject, between-day variability for the V̇O2 measures was 7.6–12.9%.
Conclusion: Because there were no day 1 to day 3 reductions in metabolic variables, day 1 to day 3 reductions at 90% FWS in net HR may reflect decreased emotional stress over time and reductions in net V̇E, an uncoupling of V̇O2 and V̇E. Despite between-day differences, reliable net physiologic and stable net metabolic variables may be collected in subjects with mild CP after one treadmill walking practice session.
Cerebral palsy (CP) is a “group of nonprogressive, but often changing, motor impairment syndromes secondary to lesions or anomalies of the brain arising early in development” (19). It occurs 2–2.5 times per 1000 live births (23). A decrease in walking proficiency and economy (5,29) is a main physical disability of spastic diplegic and hemiplegic CP, which are the most common subtypes (23). High, lower-limb antagonist muscle coactivation (29) and mechanical power (28) are associated with this low economy. Interventions to improve walking proficiency also increase walking economy; for example, orthopedic surgery (6) and bracing (15). Studies investigating mechanisms (28,29) and interventions primarily (6,15) used a treadmill walking protocol, which allows speed to be more precisely controlled than during over ground walking and electromyographic, biomechanic, and physiologic variables to be more easily collected simultaneously. Control of walking speed may be especially relevant in intervention studies. The effect of hinged ankle foot orthoses on the oxygen cost of walking, for example, is speed dependent (15).
To ensure the data from a treadmill walking protocol do not simply reflect an adaptation to the test, it has traditionally been assumed that subjects should be habituated to walking on the treadmill before testing. In healthy 7- to 11-yr-old children, who presumably have a mature gait pattern (25), Frost et al. (8) found no significant between-trial or between-day differences in oxygen uptake (V̇O2), heart rate (HR), or kinematic variables at various walking and running speeds after 15–20 s of treadmill walking practice. This suggests that, as a group, children whose gait pattern has matured require very little time to habituate to walking on the treadmill. In younger, healthy 6-yr-old children, however, whose gait pattern is likely not mature (25), V̇O2 during treadmill walking (1.34 m·s−1) even after 5 min of practice was significantly higher for the first trial than for trials 2 and 3 (within-day), although the difference was small (0.2 mL·kg−1·min−1) (27). Those under 7 yr, perhaps due to their immature motor abilities related to walking (25), appear to require more treadmill walking practice before there are no significant differences in V̇O2 between the walks.
In children and adolescents with CP, who also have an immature walking pattern (12), walking practice sessions of 15–20 min before testing have been reported in the literature (9,15,28,29), although other studies (6,21) have not stated if or how much walking practice preceded testing. After 5 min of treadmill walking practice, Keefer et al. (11) found no significant between-trial (within-day) differences in V̇O2 (trials 1 and 2 = 6.6 mL·kg−1·min−1, trial 3 = 6.2 mL·kg−1·min−1, P < 0.05) for 6- to 15-yr-olds with spastic hemiplegic CP walking on the treadmill at 0.67 m·s−1. It is unknown whether, after one practice session, V̇O2 would remain stable, or if it would further be reduced due to habituation, if subjects were tested on different days. It is also unknown whether any effects on V̇O2 of repeated walking bouts would be different at different speeds. Such information would be useful for researchers using a treadmill protocol to assess the effect on walking economy of various interventions. Because the increase in walking economy when wearing orthoses (compared with wearing only shoes) in children with mild CP is greater at faster compared with slower speeds (15), and because there was no within-day improvement in walking economy (after one practice session) for those with CP with repeated walking bouts at a slow speed (11), improvements in walking economy due to repeated waking bouts on different days in this population may be greater at faster speeds.
The purpose of this study was to determine whether after one 12–15 min practice session: i) metabolic and cardiorespiratory responses during treadmill walking in children and adolescents with spastic CP are affected by repeated walking bouts on different days and ii) these responses are different at different speeds. We hypothesized that after 12–15 min of treadmill walking practice, there would be no between-day differences in physiologic responses during walking at a relatively slow speed but that at faster speeds the responses would be lower on day 2 and day 3 compared with day 1.