Date of Award

9-2004

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Medical Sciences

Supervisor

Oded Bar-Or

Abstract

Six studies (Studies 1-6) were performed to gain insight into selected physiologic (metabolic, cardiorespiratory, thermoregulatory), electromyographic, and biomechanical implications of the high energy cost of walking in children and adolescents with mild cerebral palsy (CP). Controls (CON) were also tested in Studies 3 and 4. Studies 1 and 2 examined issues related to habituation to treadmill walking. The purpose of Study 1 was to determine if after one, 12-15-minute treadmill walking practice session: i) metabolic and cardiorespiratory responses during walking are affected by repeated walking bouts on different days, and ii) if these responses are different at different speeds. After 12-15 minutes of treadmill walking practice, subjects walked on the treadmill (3-minute bouts) at 60, 75, 90% of the fastest walking speed (FWS), on three different days. From Day 1 to Day 3, net ventilation ('VE) and net heart rate (HR) at 90% FWS decreased by 3.6 l'minute⁻¹ and 8 beats·minute⁻¹, respectively. There were no differences between Day 1 and Day 2 or Day 1 and Day 3 for any other metabolic or cardiorespiratory variable at any speed. Between-day reliability of most metabolic and cardiorespiratory responses was ~ 0.95. Since there were no Day 1 to Day 3 differences in metabolic variables, Day 1 to Day 3 decreases at 90% FWS in net HR may reflect reduced emotional stress over time and decreases in net VE, an uncoupling of oxygen uptake (V02) and VE. Despite between-day differences, it appears that reliable metabolic and cardiorespiratory data may be obtained in these subjects after one, 12-15-minute treadmill walking practice session. In Study 2 the subjects practiced walking on the treadmill as in Study 1 and, on a different day, they then walked once on the treadmill for three minutes, at 90% FWS. In this case, the purpose of the study was to determine: i) minute-by-minute differences in lower limb antagonist muscle co-activation and stride length during a 3-minute treadmill walk following 12-15 minutes of treadmill walking practice, and ii) if the minute-by-minute pattern of co-activation is affected by site (thigh or lower leg) and lower limb dominance. During the treadmill walk, non-dominant thigh co-activation decreased between minute 1 and a) minute 2 (6%), b) minute 3 (7.2%). Co-activation for the dominant lower leg decreased between minute 1 and minute 3 (11.3%). Non-dominant thigh coactivation was on average 27.3% higher than for the dominant thigh, independent of time. Thigh co-activation was on average 27.7% higher than for the lower leg, independent of dominance or time. Stride length increased between minute 1 and minute 3 by 2.1 %. These data suggest that 12-15 minutes of treadmill walking practice may be sufficient time to obtain stable co-activation and stable stride length by minute 2 of a fast treadmill walk. The data also suggest that dominance and site affect the magnitude of co-activation. The purpose of Studies 3 and 4 was to determine if children and adolescents with mild spastic CP differ from CON in their thermoregulatory responses during exercise in the heat, where such exercise would have the same oxygen (O2) cost for both groups (Study 3) and where such exercise would have a higher O2 cost for those with CP compared to CON (Study 4). Each subject with CP was individually matched to a CON. The CP subject and their CON-match arm-cranked (Study 3) or walked on the treadmill (Study 4) at the same intensity for three, 10-minute bouts in 35 °C, 50% relative humidity. In Study 3, there were no CP-CON differences in \/02 or in thermal strain. In Study 4, V02, body temperatures, and HR were higher in the CP group compared to CON (V02 was 40% higher, rectal temperature was 0.4 °C higher). Those with CP demonstrated greater thermal strain than CON during treadmill walking where they required more metabolic energy, and thus produced more metabolic heat than CON, but not during arm-cranking where their V02 was matched and heat production was therefore similar between the groups. The primary purposes of Studies 5 and 6 were to determine whether there was a relationship between the subjects' level of habitual physical activity (PA) and their 02 cost of walking (Study 5) or their biomechanical walking economy (Study 6). In both studies subjects walked on the treadmill at the same speeds and with the same amount of practice as in Study 1. HR (Study 5) and movement (Study 6) were also monitored over 2 weekdays and 1 weekend day. In Study 5 habitual PA (derived from monitored HR) was related (r = -.70 to -.84) to net V02 at 60 and 75% FWS, to net V02 m-1 , averaged across the three speeds, and to % peak \/02 at all three speeds. PA was not related to net \/02 at 90% FWS. In Study 6, biomechanical walking economy, as measured by the biomechanical economy quotient (SEQ), at 60, 75 or 90% FWS explained about half of the intersubject variance in PA as measured by accelerometer movement counts. A similar relationship was found between SEQ and accelerometer movement counts at or above the 80th and 90th percentile for both the total minutes d-1, and the number of 5-minute bouts d-1. The data from Studies 5 and 6 suggest that PA in these subjects may be related to their walking economy.

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