Validation and comparison of ActiGraph activity monitors

Objective: To compare activity counts from the ActiGraph GT3X to those from the ActiGraph GT1M during treadmill walking/running. A secondary aim was to develop tri-axial vector magnitude (VM3) cut-points to classify physical activity (PA) intensity. Methods: Fifty participants wore the GT3X and the GT1M on the non-dominant hip and exercised at 4 treadmill speeds (4.8, 6.4, 9.7, and 12 km h⁻¹). Vertical (VT) and antero-posterior (AP) activity counts (counts min⁻¹) as well as the vector magnitudes of the two axes (VM2) from both monitors were tested for significant differences using two-way ANOVA's. Bland–Altman plots were used to assess agreement between activity counts from the GT3X and GT1M. Linear regression analysis between VM3 counts min⁻¹ and oxygen consumption data was conducted to develop VM3 cut-points for moderate, hard and very hard PA. Results: There were no significant inter-monitor differences in VT activity counts at any speed. AP and VM2 activity counts from the GT1M were significantly higher (p < 0.01) than those from the GT3X at 4.8, 9.7 and 12 km h⁻¹. High inter-monitor agreement was found for VT activity counts but not for AP and VM2 activity counts. VM3 cut-points for moderate, hard, and very hard PA intensities were 2690–6166, 6167–9642, >9642 counts min⁻¹. Conclusion: Due to the lack of congruence between the AP and VM2 activity counts from the GT1M and the GT3X, comparisons of data obtained with these two monitors should be avoided when using more than just the VT axis. VM3 cut-points may be used to classify PA in future studies.     

The match-to-match variation of match-running in elite female soccer

Objectives

The purpose of this study was to examine the match-to-match variation of match-running in elite female soccer players utilising GPS, using full-match and rolling period analyses.

胸腰椎纵向撞击伤机制及影响因素探讨

目的 研究纵向撞击下胸腰椎的损伤阈值及其影响因素。 方法 将T₁₂~L₂和L₂~L₅脊柱标本各分为3组,分别施以3个能量段的撞击。撞击前后分别拍X线片和CT扫描。 结果 撞击力峰值和撞击速度随撞击能量的增加而提高,力的作用时间减少,冲量值不变。撞击后标本的最大加速度、最大速度及位移均增大。X线及CT示在低能量撞击后个别标本骨折,中能量撞击全部骨折,高能量撞击产生爆裂性骨折。 结论 撞击能量、撞击速度、撞击力峰值及标本撞的加速度、速度及最大位移可作为评价胸腰椎标本损伤与否及损伤程度的指标。     

A mechanical protocol to replicate impact in walking footwear

Impact testing is undertaken to quantify the shock absorption characteristics of footwear. The current widely reported mechanical testing method mimics the heel impact in running and therefore applies excessive energy to walking footwear. The purpose of this study was to modify the ASTM protocol F1614 (Procedure A) to better represent walking gait. This was achieved by collecting kinematic and kinetic data while participants walked in four different styles of walking footwear (trainer, oxford shoe, flip-flop and triple-density sandal). The quantified heel-velocity and effective mass at ground-impact were then replicated in a mechanical protocol. The kinematic data identified different impact characteristics in the footwear styles. Significantly faster heel velocity towards the floor was recorded walking in the toe-post sandals (flip-flop and triple-density sandal) compared with other conditions (e.g. flip-flop: 0.36 ± 0.05 m s⁻¹ versus trainer: 0.18 ± 0.06 m s⁻¹). The mechanical protocol was adapted by altering the mass and drop height specific to the data captured for each shoe (e.g. flip-flop: drop height 7 mm, mass 16.2 kg). As expected, the adapted mechanical protocol produced significantly lower peak force and accelerometer values than the ASTM protocol (p < .001). The mean difference between the human and adapted protocol was 12.7 ± 17.5% (p < .001) for peak acceleration and 25.2 ± 17.7% (p = .786) for peak force. This paper demonstrates that altered mechanical test protocols can more closely replicate loading on the lower limb in walking. This therefore suggests that testing of material properties of footbeds not only needs to be gait style specific (e.g. running versus walking), but also footwear style specific.     

The effect of choice reaction task on impact of single-leg landing

This study aimed to investigate attentional demand during single-leg landing after a jump. The experiment was set up as dual-task test. Twelve healthy male participants were instructed to make a two-leg jump with right-leg landing as softly as possible. The flight time of the jump was set to 300 ms through sufficient practice. As a cognitive task, the participants were asked to push the right or left custom-made button as soon as a go-signal was presented. The timing when the go-signal presented varied from 0 to 300 ms from the take-off. Catch trials in which the go-signal was not presented were randomly inserted. The results showed that the maximum vertical ground reaction force after touchdown was greater under the dual-task condition than in the single-task condition. Increase in the maximum vertical ground reaction force was consistent regardless of the timing of presenting the go-signal, and the same effect was observed in the catch trials. These results indicate that the effect of dual tasking was caused by attentional allocation to the choice reaction time task. Athletes may be exposed a large ground reaction forces during landing while performing cognitive tasks.     

Primarily hip-borne load carriage does not alter biomechanical risk factors for overuse injuries in soldiers

Objectives

To determine the effects of different body armour types, carried loads, and walking speeds on trunk and lower-limb joint biomechanics.

Variability of within-step acceleration and daily wellness monitoring in Collegiate American Football

Objectives

It is commonplace to consider accelerometer load and any resultant neuromuscular fatigue in training programs. With these data becoming accepted in sport alongside wellness questionnaires this study aimed to investigate if a deeper analysis of the accelerometry data can provide actionable insight into training-induced disruptions.

Injury risk-workload associations in NCAA American college football

Objectives

To determine injury risk-workload associations in collegiate American Football.

The influence of sleep and training load on illness in nationally competitive male Australian Football athletes: A cohort study over one season

Objectives

To determine the incidence of illness, and identify the relationship between sleep, training load and illness in nationally competitive Australian football athletes. Second, to assess multivariate effect between training load and/or sleep variables.

The reproducibility of signals from skin-mounted accelerometers following removal and replacement

Signals from skin-mounted accelerometers may contain measurement error when compared to those obtained from bone-mounted sensors. While this error may be minimized through various techniques, additional error may arise as a result of accelerometer removal from the skin and subsequent replacement. The purpose of this experiment was to determine if skin-mounted accelerometer signals remain similar before and after sensor replacement when sensors are stimulated within a consistent vibration environment. The spines of five porcine and five human cadavers were vibrated non-invasively and the resulting response measured using accelerometers glued to the skin overlying the vertebrae of interest (T-9 in porcine cadavers, L2-L4 in human cadavers). Accelerometers were removed, then replaced, to their perceived original positions. Accelerometer signals showed high repeatability within an original placement, however, once replaced, pre- and post-replacement signals were statistically dissimilar in all cadavers tested. Specifically, the similarity of pre- and post-replacement signals was poor for different skin types (porcine and human) and did not improve with accelerometer proximity to the vibration source. From these data, we conclude that accelerometers adhered to the skin overtop spinous processes are able to obtain highly repeatable signals for a given placement, however, signals change significantly after sensor replacement. When skin-mounted accelerometers are used in gait and other studies, investigators should consider performing test/re-test analyses to ensure that sensor data are not affected if sensor replacement is required by design or by accident.     

Equating accelerometer estimates of moderate-to-vigorous physical activity: In search of the Rosetta Stone

No universally accepted ActiGraph accelerometer cutpoints for quantifying moderate-to-vigorous physical activity (MVPA) exist. Estimates of MVPA from one set of cutpoints cannot be directly compared to MVPA estimates using different cutpoints, even when the same outcome units are reported (MVPA min d^–1). The purpose of this study was to illustrate the utility of an equating system that translates reported MVPA estimates from one set of cutpoints into another, to better inform public health policy. Secondary data analysis. ActiGraph data from a large preschool project (N = 419, 3–6-yr-olds, CHAMPS) was used to conduct the analyses. Conversions were made among five different published MVPA cutpoints for children: Pate (PT), Sirard (SR), Puyau (PY), Van Cauwengerghe (VC), and Freedson Equation (FR). A 10-fold cross-validation procedure was used to develop prediction equations using MVPA estimated from each of the five sets of cutpoints as the dependent variable, with estimated MVPA from one of the other four sets of cutpoints (e.g., PT MVPA predicted from FR MVPA). The mean levels of MVPA for the total sample ranged from 22.5 (PY) to 269.0 (FR) min d⁻¹. Across the prediction models (5 total), the median proportion of variance explained (R²) was 0.76 (range 0.48–0.97). The median absolute percent error was 17.2% (range 6.3–38.4%). The prediction equations developed here allow for direct comparisons between studies employing different ActiGraph cutpoints in preschool-age children. These prediction equations give public health researchers and policy makers a more concise picture of physical activity levels of preschool-aged children.     

Validation of a pouch-mounted activPAL3 accelerometer

The activPAL accelerometer is a commonly used device for the assessment of physical activity in cross-sectional and intervention research. These devices are usually attached directly to the skin; however, recent studies report problems such as skin irritation associated with this attachment method and therefore adequate alternate methods are needed. The aim of this study was to validate the use of an elasticised pouch to secure an activPAL3c (PAL Technologies, Glasgow, UK) accelerometer for the assessment of sedentary and physical activity behaviours during laboratory and free-living conditions. Twenty-eight healthy adults wore two activPAL3c accelerometers, one secured in an elasticised pouch, and one directly attached to the skin, on the anterior surface of the right thigh during laboratory-based walking at a self-selected pace, treadmill walking at 0.89 m s⁻¹, 1.56 m s⁻¹ and running at 2.2 m s⁻¹, and during free-living conditions. Paired samples t-tests and intraclass correlation coefficients were used to investigate the difference and agreement between accelerometer outputs. No statistically significant difference in step count between pouch-mounted and skin-mounted activPAL3c accelerometers was evident during walking at any speed under laboratory conditions. No statistically significant difference in step count, upright time, sitting time or postural transitions was found between pouch-mounted and skin-mounted activPAL3c accelerometers during free-living conditions. Intraclass correlation coefficients showed a high to very high level of agreement between pouch-mounted and skin-mounted activPAL3c accelerometers for each outcome variable. The use of an elasticised pouch to secure the activPAL3c accelerometer appears to be a valid method of attachment and may offer advantages over direct skin mounting.