Anaerobic performance in 5- to 7-yr-old children of low birthweight.

PURPOSE: This study was intended to determine whether anaerobic muscle performance is deficient in 5- to 7-yr-old children of extremely low birthweight (ELBW, 500-999 g) and very low birthweight (VLBW, 1000-1499 g). METHODS: Fourteen ELBW and 20 VLBW children were compared with 24 normal birthweight (NBW, >2500 g) term controls. Peak (PP) and mean (MP) muscle power were determined by the Wingate anaerobic test. Bioimpedance analysis and anthropometry were done to assess fat-free mass (FFM) and lean cross-sectional area of the thigh and calf. RESULTS: The ELBW group had significantly lower MP and PP, compared with the VLBW and, in particular, with the NBW group. This lower performance was apparent also when values were corrected for total body mass (MP) and FFM (MP and PP), but not when corrected for cross-sectional area of thigh and calf. CONCLUSION: The lower anaerobic muscle performance in ELBW children may be partly due to their smaller muscle mass, but may also reflect a low percentage of fast-twitch muscle fibers, low muscle phosphagen content, or deficiency in motor control.

Impact of a single exercise bout on energy expenditure and spontaneous physical activity of obese boys.

The main objective of the present study was to determine whether a structured, laboratory-based exercise task would modify the energy expenditure (EE) and the pattern of spontaneous physical activity (PA) of obese boys on the day of an exercise laboratory visit and on the following day. Fourteen 10- to 15-y-old moderately obese (36.6+/-3.3% fat) boys volunteered. They each had three laboratory visits, I wk apart. In one visit, they performed a strenuous 50-min cycling task; in another, a 30-min medium-intensity cycling task; and in another (which served as placebo), they did not exercise. PA was monitored the day before (d 1), during (d 2), and after (d 3) each laboratory visit by use of a heart rate monitor and a 12-h recall interview. EE was calculated from minute-by-minute heart rate and each child's predetermined relationship between oxygen uptake and heart rate. EE and PA were analyzed from 1300 to 1900 h each day using 15-min intervals. EE tended to decrease (p < 0.087) in the afternoon of all d 2 compared with d 1, and it increased on d 3 after the medium-intensity exercise (p < 0.0005). EE during d 2 and 3 combined, compared with d 1, decreased after the high-intensity exercise (534.2 versus 564.3 kJ/h, p < 0.05). It increased after the medium-intensity exercise (561.8 versus 526.7 kJ/h, p = 0.052) and was not affected after the placebo visit (589.4 versus 574.3 kJ/h). Time spent outdoors was consistently reduced on the day of laboratory visit compared with the day before and after the visit, regardless of the contents of intervention. In conclusion, a single laboratory visit is followed by a reduction in EE and PA on the day of intervention. However, its effect on EE the following day may be dose dependent: medium-intensity exercise induces an increase in EE, but high-intensity exercise causes a decrease in EE. One implication is that intervention by physical training should employ medium-intensity exercise to enhance the EE of obese boys.

Glucose ingestion matched with total carbohydrate utilization attenuates hypoglycemia during exercise in adolescents with IDDM.

There are currently no guidelines regarding the carbohydrate (CHO) dosage required to prevent exercise-induced hypoglycemia in children with insulin-dependent diabetes mellitus (IDDM). To prevent hypoglycemia by matching glucose ingestion with total-CHO utilization, 20 adolescents with IDDM attended 2 trials: control (CT; drinking water) and glucose (GT; drinking 6-8% glucose). Participants performed 60 min of moderate-intensity cycling 100 min after insulin injection and breakfast. CT's total-CHO utilization during exercise was determined using indirect calorimetry. In GT, participants ingested glucose in the amount equal to total CHO utilization in the CT. A total of 9 participants had BG < 4.0 mmol/L in CT compared to 3 in GT (p < .05). In conclusion, glucose ingestion equal to total-CHO utilization attenuates the drop in blood glucose and reduces the likelihood of hypoglycemia during exercise in adolescents with IDDM.

Neuromotor ability in 5- to 7-year-old children with very low or extremely low birthweight.

This study was intended to determine the effects of extremely low birthweight (ELBW, 500 to 999 g) and very low birthweight (VLBW, 1000 to 1499 g) on neuromotor ability in 5- to 7-year-old children. Fourteen ELBW and 20 VLBW children were compared with 24 term control children of normal birthweight (NBW, >2500 g). Using quantitative assessment instruments, the following data were collected: maximal cycling speed during 30 seconds of cycling at 'zero' resistance, simple reaction time of the legs, and performance on components of a whole-body coordination test. The main findings were a slower reaction time, lower maximal cycling speed, and lower coordination scores in the ELBW group compared with the NBW group and, for some variables, with the VLBW group. The reduced motor performance in these children appears for the most part to be a reflection of impaired neuromotor control and motor development, rather than merely a smaller body or muscle size.

Cocontraction and phasic activity during GAIT in children with cerebral palsy.

Simultaneous activity of agonist and antagonistic muscles during a task is known as cocontraction. The primary aim of the present study was to use a cocontraction index (CI) to quantify differences in EMG activity between a group of CP and control children at two different walking speeds. The secondary aim was to compare the amount of time the muscles were activated ("on" thresholds) between the groups. Seventeen subjects volunteered for the study. One group consisted of 9 (7M, 2F) children with CP (age 12.7 +/- 2.8 years, mean +/- SD). The second group consisted of 8 able-bodied controls (7M, 1F). The discontinuous submaximal treadmill walking protocol had two 4min stages at 0% gradient. Speeds selected were 3 km.h-1 and 90% of the pre-determined fastest walking speed (FWS). Two sites of CI were measured from the EMGs of tibialis anterior and soleus (leg) and vastus lateralis and hamstrings (thigh). Significantly (p < 0.05) higher CI values were noted for the CP subjects compared to the controls, irrespective of speed or cocontraction site and there was a significant (p < 0.05) increase in CI values with increased walking speed for both CP and control subjects. Phasic analyses for 5% max EMG and 10% max EMG "on" thresholds demonstrated significant (p < 0.05) main effects for group (CP subjects had a longer time period of muscle activation than controls) and speed (muscles were active longer at 90% FWS than 3 km.h-1). The precise mechanisms by which cocontraction contributes toward abnormal gait and wasted mechanical energy require further research incorporating both electromyographic and kinematic analysis.