Seasonal variation in the distribution of daily stepping in 11-13 year old school children.

PURPOSE: Seasonality studies in adolescent's physical activity (PA) tend to report total PA (e.g. steps/day) rather than more specific detail such as steps/hour. This study compared the detailed changes in PA between seasons. METHODS: Thirty three adolescents (baseline age 12.2 ± 0.3y) wore the activPAL activity monitor for 8 days on two occasions. RESULTS: Steps/day were higher in summer (Mdn = 12,879) than winter (Mdn = 10,512), p<.001. Steps/hour were significantly higher in summer compared to winter between 17:00 and 21:00 (p<. 044). No steps/day differences were found between boys and girls at either time point (p>.05), however, boys had significantly higher step counts in summer between '13:00-14:00' (p=.023), '19:00-20:00' (p=.032) and '20:00-21:00' (p=.023). CONCLUSION: Total steps/day masked sex differences within specific hours of the day, particularly evening times. Detailed daily patterns of PA are required to fully understand differences between sexes and across seasons.

The prevalence of upright non-stepping time in comparison to stepping time in 11-13 year old school children across seasons.

Evidence suggests that behaviours such as standing are beneficial for our health. Unfortunately, little is known of the prevalence of this state, its importance in relation to time spent stepping or variation across seasons. The aim of this study was to quantify, in young adolescents, the prevalence and seasonal changes in time spent upright and not stepping (UNSt(time)) as well as time spent upright and stepping (USt(time)), and their contribution to overall upright time (U(time)). Thirty-three adolescents (12.2 ± 0.3 y) wore the activPAL activity monitor during four school days on two occasions: November/December (winter) and May/June (summer). UNSt(time) contributed 60% of daily U(time) at winter (Mean = 196 min) and 53% at summer (Mean = 171 min); a significant seasonal effect, p < 0.001. USt(time) was significantly greater in summer compared to winter (153 min versus 131 min, p < 0.001). The effects in UNSt(time) could be explained through significant seasonal differences during the school hours (09:00-16:00), whereas the effects in USt(time) could be explained through significant seasonal differences in the evening period (16:00-22:00). Adolescents spent a greater amount of time upright and not stepping than they did stepping, in both winter and summer. The observed seasonal effects for both UNSt(time) and USt(time) provide important information for behaviour change intervention programs.

Re-attachment of the tuberosities of the humerus following hemiarthroplasty for four-part fracture.

This study evaluated the effect on movement under load of three different techniques for re-attachment of the tuberosities of the humerus using test sawbones. In the first, the tuberosities were attached both to the shaft and to each other, with one cerclage suture through the anterior hole in the prosthesis. The second technique was identical except for omission of the cerclage suture and in the third the tuberosities were attached to the prosthesis and to the shaft. An orthogonal photogrammetric system allowed all segments to be tracked in a 3D axis system. The humeri were incrementally-loaded in abduction, and the 3D linear and angular movements of all segments were calculated. Displacement between the tuberosities and the shaft was measured. The first and second techniques were the most stable constructs, with the third allowing greater separation of fragments and angular movement. Separation at the midpoint of the tuberosities was significantly greater using the latter technique (p < 0.05). The cerclage suture added no further stability to the fixation.

Regression analysis of gait parameters with speed in normal children walking at self-selected speeds.

Dimensionless analysis ensures that differences in sizes (e.g. height and weight) of children have a minimal influence on gait parameters. The results of changes in speed on gait parameters were examined using dimensionless analysis on data from a prospective 5-year study of 16 children. Linear regression analysis of peak and trough values of temporal distance parameters, ground reaction forces, joint angles, moments and powers provide a quantitative description of gait development with normalised speed. These linear relationships can be used to estimate gait parameters from speed measurements for normal subjects. However, caution is advised in using the data to attempt to predict an individual's gait parameters due to the wide spread of data about the regression lines and we do not recommend that the data be used to extrapolate the regression data to wider speed ranges.

Direct comparison of calculated hip joint contact forces with those measured using instrumented implants. An evaluation of a three-dimensional mathematical model of the lower limb.

Characterisation of hip joint contact forces is essential for the definition of hip joint prosthesis design requirements. In vivo hip joint contact force measurements have been made using instrumented hip joint prostheses. However, to allow determination of the range of values of joint contact force and their directions relative to anatomical structures in a range of subject groups sufficient to form an agreed data base it is necessary to adopt a different approach without the use of an implanted transducer. The use of mathematical models of the lower limb to examine the forces in soft tissues and at the joints has provided valuable insight into internal loading conditions. Several authors have proposed mathematical musculo-skeletal models. However, there have been only limited attempts at validation of these models. It is possible to use the results of in vivo force measurements from instrumented prostheses to validate the results calculated using the mathematical models. In this study two subjects with instrumented hip joint prostheses were studied. Forces at the hip joints were calculated using a three-dimensional model of the leg. Walking at slow, normal and fast speeds (0.97-2.01m/s), weight transfer from two to one leg and back again, and sit to stand were studied. Direct comparisons were made between the 'gold standard' measured hip joint contact forces and the calculated forces. There was general agreement between the calculated and measured forces in both pattern and magnitude. There were, however, discrepancies. Reasons for these differences in results are discussed and possible model developments suggested.

Normalisation of gait data in children.

The comparative effect of semi-dimensional (SD) and non-dimensional (ND) normalisation on the results of a longitudinal study of gait in 5-12-year old children was investigated. The use of both height and leg length in the normalisation was examined. Only ND analysis could be used to identify subjects with the same accelerations. ND analysis of the children's gait indicated that there was little change in the combination of step length and cadence used to achieve a particular velocity between 5 and 12. The first peak and mid-stance trough values of the vertical component of ground reaction force did not change with age. We recommend the use of ND normalisation rather that SD to allow comparisons between individuals of differing size and mass.

Hip joint contact forces in normal subjects and subjects with total hip prostheses: walking and stair and ramp negotiation.

OBJECTIVE: To calculate the hip joint contact force in normal subjects and subjects with total hip replacements. DESIGN: An observational study of age matched normal subjects and subjects with hip joint replacements. BACKGROUND: Hip joint contact forces have been calculated using musculo-skeletal models and measured in vivo using instrumented hip prostheses. There are few examples of studies performed on subjects in the 40-60 year age range. This study characterises the forces in both normal subjects and subjects with hip joint replacements for these 'young' subjects. METHODS: Motion analysis and force plate data were used as input to a three-dimensional model of the leg. Five male and six female normal subjects and five male subjects with hip prostheses were studied. Each subject was observed walking and negotiating stairs and a ramp. RESULTS: Hip joint contact forces in both thigh and pelvic-based co-ordinate systems are presented. Subjects cadence, speed and stride length are given. CONCLUSIONS: In general subjects with hip replacements exhibited lower hip joint contact forces than age matched normal subjects. It is suggested that this was the results of the lower speeds, stride lengths and cadences adopted by the subjects with hip replacements. RELEVANCE: The characterisation of hip joint contact forces provides essential information for prosthetic joint design and testing. The comparison of hip joint contact forces in normal subjects with those in subjects with prosthetic joints provides evidence of, not only actual use of joints, but also of possible levels of force that might be applied to hip prostheses if subjects returned to normal use.

Sagittal joint kinematics, moments, and powers are predominantly characterized by speed of progression, not age, in normal children.

Twenty-six healthy 7-year-old children were enrolled in a 5-year longitudinal study to examine the importance of age and speed in the characterization of sagittal joint angles, moments, and powers. In 740 gait trials, children walking at self-selected speeds were examined on the basis of age and normalized speed [speed/(height x g)1/2]. The kinematics and kinetics in these children were characterized predominantly by normalized speed of progression and not age. The clinical relevance of these findings is that normalized speed of walking, rather than age, should be considered when comparing normal with pathologic gait.

Normalized speed, not age, characterizes ground reaction force patterns in 5-to 12-year-old children walking at self-selected speeds.

Twenty-six healthy 5-year-old children were enrolled in a 7-year longitudinal study to examine the importance of age and speed in the characterization of ground reaction forces. One thousand forty gait trials of children walking at self-selected speeds were examined on the basis of age and normalized speed [speed/(height x g)(1/2)]. Results, presented as discrete peak and trough values and as continuous trace plots over the stance phase, indicated that there was little change in ground reaction forces with age, but there were significant changes in vertical force and anterior-posterior force values with normalized speed. The ground reaction force patterns in these children were characterized predominantly by normalized speed of progression and not age. The clinical relevance of these findings is that normalized speed of walking, rather than age, should be considered when comparing normal with pathological gait.