Stanley Grant

Objective measurement of physical activity and sedentary behaviour: review with new data

Objective methods are being used increasingly for the quantification of the amount of physical activity, intensity of physical activity and amount of sedentary behaviour in children. The accelerometer is currently the objective method of choice. In this review we address the advantages of objective measurement compared with more traditional subjective methods, notably the avoidance of bias, greater confidence in the amount of activity and sedentary behaviour measured, and improved ability to relate variation in physical activity and sedentary behaviour to variation in health outcomes. We also consider unresolved practical issues in paediatric accelerometry by critically reviewing the existing evidence and by providing new evidence.

A comparison of methods of predicting maximum oxygen uptake.

The aim of this study was to compare the results from a Cooper walk run test, a multistage shuttle run test, and a submaximal cycle test with the direct measurement of maximum oxygen uptake on a treadmill. Three predictive tests of maximum oxygen uptake--linear extrapolation of heart rate of VO2 collected from a submaximal cycle ergometer test (predicted L/E), the Cooper 12 min walk, run test, and a multi-stage progressive shuttle run test (MST)--were performed by 22 young healthy males (mean(s.d.) age 22.1 (2.4) years; body mass 72.4(8.9kg)) and the values compared to those obtained by direct measurement on a maximal treadmill test. All of the subjects were regular exercisers. The mean(s.d.) from the various tests in ml.kg-1.min-1 were as follows: treadmill 60.1(8.0), Cooper 60.6(10.3), MST 55.6(8.0), and predictedL/E 52.0(8.4). The Cooper test had a correlation with the treadmill test of 0.92, while the MST and the predictedL/E had correlations of 0.86 and 0.76 respectively. Both the MST and predictedL/E showed systematic underprediction of the treadmill value. On average, the MST was 4.5 ml.kg-1.min-1 (s.e. 0.9) lower than the treadmill VO2max while the predictedL/E was 7.8 ml.kg-1. min-1 (s.e. 1.4) lower than the treadmill VO2max. These findings indicate that, for the population assessed, the Cooper walk run test is the best predictor of VO2max among the three tests.

Effect of socioeconomic status on objectively measured physical activity

Background: A socioeconomic gradient in childhood obesity is known to be present by the age of school entry in the UK. The origin of this gradient is unclear at present, but must lie in socioeconomic differences in habitual physical activity, sedentary behaviour, or dietary intake. Aims: To test the hypothesis that habitual physical activity and/or sedentary behaviour are associated with socioeconomic status (SES) in young Scottish children. Methods: Observational study of 339 children (mean age 4.2 years, SD 0.3) in which habitual physical activity and sedentary behaviour were measured by accelerometry over six days (study 1). In a second study, 39 pairs of children of distinctly different SES (mean age 5.6 years, SD 0.3) were tested for differences in habitual physical activity and sedentary behaviour by accelerometry over seven days. Results: In study 1, SES was not a significant factor in explaining the amount of time spent in physical activity or sedentary behaviour once gender and month of measurement were taken into account. In study 2, there were no significant differences in time spent in physical activity or sedentary behaviour between affluent and deprived groups. Conclusion: Results do not support the hypothesis that low SES in young Scottish children is associated with lower habitual physical activity or higher engagement in sedentary behaviour.

Lactate threshold responses to a season of professional British youth soccer

Objective: To examine the changes in aerobic endurance performance of professional youth soccer players throughout the soccer season. Methods: Nine youth soccer players were tested at six different time points throughout the soccer season by sub-maximal blood lactate assessment, using an incremental treadmill protocol. Whole blood lactate concentration and heart frequency (Hf) were determined at each exercise stage. Running velocities at the first lactate inflection point (v-Tlac) and at a blood lactate concentration of 4 mmol l−1 (v-4mM) were determined. Results: Running velocity at the two lactate thresholds increased from the start of pre-season training to the early weeks of the competitive season, from 11.67 (0.29) to 12.96 (0.28) km h−1 for v-Tlac, and from 13.62 (0.25) to 14.67 (0.24) km h−1 for v-4mM (p<0.001). However, v-Tlac and v-4mM when expressed relative to maximum heart frequency (Hfmax) remained unchanged. The Hf to blood lactate concentration relationship was unchanged after the pre-season training period. The two expressions of lactate threshold did not reveal differences between each other. Conclusion: Running velocity at v-Tlac and v-4mM increased significantly over the pre-season period, but v-Tlac and v-4mM were unchanged when expressed relative to Hfmax. This finding may indicate that increased endurance performance may be mainly attributable to alterations in Vo2max. Although lactate assessment of soccer players is useful for determining endurance training adaptations in soccer players, additional assessment of the other two determinants of endurance performance (Vo2max and running economy) may provide more useful information for determining physiological adaptations resulting from soccer training and training interventions.

A comparison of the anthropometric, strength, endurance and flexibility characteristics of female elite and recreational climbers and non-climbers

There is limited information on the anthropometry, strength, endurance and flexibility of female rock climbers. The aim of this study was to compare these characteristics in three groups of females: Group 1 comprised 10 elite climbers aged 31.3 ± 5.0 years (mean ± s ) who had led to a standard of ‘hard very severe’; Group 2 consisted of 10 recreational climbers aged 24.1 ± 4.0 years who had led to a standard of ‘;severe’; and Group 3 comprised 10 physically active individuals aged 28.5 ± 5.0 years who had not previously rock-climbed. The tests included finger strength (grip strength, finger strength measured on climbing-specific apparatus), flexibility, bent arm hang and pull-ups. Regression procedures (analysis of covariance) were used to examine the influence of body mass, leg length, height and age. For finger strength, the elite climbers recorded significantly higher values ( P < 0.05) than the recreational climbers and non-climbers (four fingers, right hand: elite 321 ± 18 N, recreational 251 ± 14 N, non-climbers 256 ± 15 N; four fingers, left hand: elite 307 ± 14 N, recreational 248 ± 12 N, non-climbers 243 ± 11 N). For grip strength of the right hand, the elite climbers recorded significantly higher values than the recreational climbers only (elite 338 ± 12 N, recreational 289 ± 10 N, non-climbers 307 ± 11 N). The results suggest that elite climbers have greater finger strength than recreational climbers and non-climbers.

The relationship between 3 km running performance and selected physiological variables

The aim of this study was to assess the relationship between a number of physiological variables and running velocity at 3 km (v-3km) in a group of male runners. Sixteen well-trained middle- and long-distance runners (mean +/-s: age 22.4 +/- 4.2 years, body mass 63.5 +/- 6.2 kg, VO2 max 73.3 +/- 6.7 ml kg-1 min-1) underwent laboratory treadmill tests to determine their maximum oxygen uptake (VO2 max), running economy at three submaximal velocities (12.9, 14.5 and 16.1 km h-1 or 14.5, 16.1 and 17 km h-1), predicted velocity at VO2 max (v-VO2max), velocity (v-Tlac) and VO2 (VO2-Tlac) at the lactate threshold and their velocity (v-4mM) and VO2 (VO2-4mM) at a blood lactate concentration of 4 mM. Distance running performance was determined by 3 km time-trials on an indoor 200 m track for which the average time was 9.46 +/- 0.74 min. The mean (+/-s) velocities for v-Tlac, v-4mM and v-VO2max were 16.0 +/- 1.8, 17.1 +/- 1.9 and 20.7 +/- 2.1 km h-1 respectively, all significantly different on average (all P < 0.05) from that for v-3km (19.1 +/- 1.5 km h-1). Many of these physiological variables were found to be individually (and significantly at 5%) related to v-3km. The best single predictors of v-3km were v-Tlac and v-4mM (both with a sample correlation, r2 of 0.93), while v-VO2max was slightly poorer (r = 0.86). Neither VO2 max nor running economy was strongly correlated with v-3km. A stepwise multiple-regression analysis revealed that v-Tlac alone was the best single predictor of v-3km and explained 87% of the variability in 3 km running velocity, while the addition of any of the other physiological variables did not significantly improve the prediction of v-3km. We conclude that, in a group of well-trained runners, the running velocity at the lactate threshold was all that was required to explain a large part of the variability in 3 km running performance.

Randomized controlled trial of quadriceps training after proximal femoral fracture

Objective: To determine whether systematic progressive high-intensity quadriceps training increases leg extensor power and reduces disability in patients rehabilitating after proximal femoral fracture. Design: Open parallel group randomized controlled trial comparing the addition of six weeks quadriceps training (40 patients) with standard physiotherapy alone (40 patients). The training group exercised twice weekly, with six sets of 12 repetitions of knee extension (both legs), progressing up to 80% of their one-repetition maximum. Setting: Orthogeriatric unit, and community follow-up. Subjects: Eighty patients rehabilitating after proximal femoral fracture. Main outcome measures: Measurements of leg extensor power (Nottingham Power Rig), functional mobility (elderly mobility score), disability (Barthel Index) and quality of life (Nottingham Health Profile) were made at baseline, after six weeks (at the end of the intervention) and at 16 weeks. Results: Leg extensor power increased significantly in the quadriceps training group (fractured leg mean improvement at six weeks 157% (standard error 16), nonfractured leg 80% (12)) compared with the control group (63% (11) and 26% (8) respectively, unpaired Students t-test p = 0.007 and p = 0.01 for between-group comparisons). Significant benefits were maintained at 16 weeks. Quadriceps training resulted in a greater increase in elderly mobility scale score compared with standard rehabilitation (between-group difference of 2.5 (95% CI 1.1,3.8) at week 6 and 1.9 (0.4,3.4) at week 16). Barthel score increased significantly from week 0 to 6 in the quadriceps training group compared with controls (Mann–Whitney U-test p = 0.05). Patients in the quadriceps training group scored significantly better in the energy subscore of the Nottingham Health Profile at the end of follow-up (Mann–Whitney U-test p = 0.0185). Conclusions: Progressive high-intensity quadriceps training in elderly proximal femoral fracture patients increased leg extensor power and reduced disability. This was accompanied by an increase in energy as measured by the Nottingham Health Profile. This intervention may provide a simple practical way of improving outcome in these patients.

The effect of towing a range of relative resistances on sprint performance

The aim of this study was to compare sprint performance over 10 and 20 m when participants ran while towing resistances, weighing between 0 and 30% of body mass. The sample of 33 participants consisted of male rugby and soccer players (age 21.1 ± 1.8 years, body mass 83.6 ± 13.1 kg, height 1.82 ± 0.1 m; mean ± s). Each participant performed two sets of seven sprints over 20 m using a Latin rectangular design. The times were recorded at 10 and 20 m using electronic speed gates. The sprints of 13 players were video-recorded to allow calculation of stride length and frequency. For both sprints, a quadratic relationship was observed between sprint time and resistance as sprint time increased from 2.94 s to 3.80 s from 0 to 30% resistance. This relationship was statistically significant but considered not to be meaningful for performance because, over the range of resistances used in this study, the quadratic model was never more than 1% (in terms of sprint time) from the linear model. As resistance increased, the stride length shortened, with mean values of 1.63 ± 0.13 m at 0% body mass and 1.33 ± 0.13 m at 30% of body mass. There was no significant change in stride frequency with increasing resistance. The results show that in general there is an increase in sprint time with an increase in resistance. No particular resistance in the range tested (0 – 30%) can be recommended for practice.

A comparison of physiological responses and rating of perceived exertion in two modes of aerobic exercise in men and women over 50 years of age.

Objectives: To compare the physiological responses and ratings of perceived exertion to aerobic dance and walking sessions completed at a self selected pace. Methods: Six women and six men with a sample mean (SD) age of 68 (7) years completed aerobic dance and walking sessions in random order. A treadmill test was performed by each subject from which peak oxygen uptake (V̇o2) and maximum heart rates (HRmax) were determined. During the aerobic dance and walking sessions, heart rate and V̇o2 were measured continuously throughout. Rate of perceived exertion (RPE) was measured every three minutes throughout the session. Results: The sample means (SD) for %peak V̇o2 were 67 (17)% for the aerobic dance sessions and 52 (10)% for the walking sessions, and the %HRmax sample means (SD) were 74 (12)% for the aerobic dance sessions and 60 (8)% for walking sessions. The sample mean (SD) RPE for the aerobic dance sessions was 11 (2), and for the walking sessions it was 10 (2). Conclusions: %peak V̇o2, %HRmax, and RPE were significantly higher for aerobic dance than for walking. However, both the aerobic dance and walking sessions were of adequate intensity to improve aerobic fitness in most subjects. Further investigation into the relation between RPE and %peak V̇o2 in a field setting over representative exercise time periods would be useful.

Resting heart rate definition and its effect on apparent levels of physical activity in young children.

PURPOSE Heart rate monitoring is widely used to measure physical activity in children, but it may be dependent on the definition of resting heart rate used and the protocol used to measure or derive resting heart rate (RHR). The aim of this study was to determine the effect of RHR definition on activity levels assessed by PAHR-25 (% time at >25% of RHR), PAHR-50 (% time at >50% of RHR), and activity heart rate (AHR; mean HR minus RHR). METHODS Minute-to-minute heart rates were measured over 3 d in 20 healthy preschool children aged 3-4 yr. Resting heart rate was measured for 5 min after a 10-min rest and was also derived from the following different but commonly used protocols: 1) mean of lowest heart rate plus all heart rates within three beats; 2) mean of lowest 5; 3) lowest 10; 4) lowest 50. This gave five different definitions of RHR. Differences in RHR and in the derived indices of activity among definitions were tested for agreement using a Bland-Altman analysis, and by rank order correlation. RESULTS Differences in RHR among all definitions were statistically significant. These resulted in significant differences in apparent physical activity levels: PAHR-25 varied 10-50% depending on the protocol used to define RHR; PAHR-50 varied by 16-65% as a function of the protocol used to define RHR. However, the different definitions of RHR had no significant influence on physical activity level when children were rank ordered. CONCLUSION Choice of method for defining RHR has a profound effect on the apparent level of activity of children. This does not alter the relative assessment of activity by rank order. A consensus definition of RHR is desirable if comparisons of activity levels between samples or populations are to be made and if the adequacy of physical activity levels is to be assessed using heart rate.