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Purpose: This study aimed to apply open-source analysis code to raw habitual physical activity data from wrist-worn monitors to: 1) objectively, unobtrusively, and accurately discriminate between "running" and "nonrunning" days; and 2) develop and compare simple accelerometer-derived metrics of external training load with existing self-report measures., Methods: Seven-day wrist-worn accelerometer (GENEActiv; Activinsights Ltd, Kimbolton, UK) data obtained from 35 experienced runners (age, 41.9 ± 11.4 yr; height, 1.72 ± 0.08 m; mass, 68.5 ± 9.7 kg; body mass index, 23.2 ± 2.2 kg·m; 19 [54%] women) every other week over 9 to 18 wk were date-matched with self-reported training log data. Receiver operating characteristic analyses were applied to accelerometer metrics ("Average Acceleration," "Most Active-30mins," "Mins≥400 mg") to discriminate between "running" and "nonrunning" days and cross-validated (leave one out cross-validation). Variance explained in training log criterion metrics (miles, duration, training load) by accelerometer metrics (Mins≥400 mg, "workload (WL) 400-4000 mg") was examined using linear regression with leave one out cross-validation., Results: Most Active-30mins and Mins≥400 mg had >94% accuracy for correctly classifying "running" and "nonrunning" days, with validation indicating robustness. Variance explained in miles, duration, and training load by Mins≥400 mg (67%-76%) and WL400-4000 mg (55%-69%) was high, with validation indicating robustness., Conclusions: Wrist-worn accelerometer metrics can be used to objectively, unobtrusively, and accurately identify running training days in runners, reducing the need for training logs or user input in future prospective research or commercial activity tracking. The high percentage of variance explained in existing self-reported measures of training load by simple, accelerometer-derived metrics of external training load supports the future use of accelerometry for prospective, preventative, and prescriptive monitoring purposes in runners.

Background: Previous research has reported peak vertical acceleration and peak loading rate thresholds beneficial to bone mineral density (BMD). Such thresholds are difficult to translate into meaningful recommendations for physical activity. Cadence (steps/min) is a more readily interpretable measure of ambulatory activity., Objective: To examine relationships between cadence, peak vertical acceleration and peak loading rate during ambulation and identify the cadence associated with previously reported bone-beneficial thresholds for peak vertical acceleration (4.9 g) and peak loading rate (43 BW/s)., Methods: Ten participants completed 8 trials each of: slow walking, brisk walking, slow running, and fast running. Acceleration data were captured using a GT3×+ accelerometer worn at the hip. Peak loading rate was collected via a force plate., Results: Strong relationships were identified between cadence and peak vertical acceleration (r = .96, P < .05) and peak loading rate (r = .98, P < .05). Regression analyses indicated cadences of 157 ± 12 steps/min (2.6 ± 0.2 steps/s) and 122 ± 10 steps/min (2.0 ± 0.2 steps/s) corresponded with the 4.9 g peak vertical acceleration and 43 BW/s peak loading rate thresholds, respectively., Conclusions: Cadences ≥ 2.0 to 2.6 steps/s equate to acceleration and loading rate thresholds related to bone health. Further research is needed to investigate whether the frequency of daily occurrences of this cadence is associated with BMD.

Purpose: The aims of this study were to quantify the relation between ground reaction force (GRF) and peak acceleration from hip- and wrist-worn accelerometers and determine peak acceleration cut-points associated with a loading rate previously demonstrated as beneficial to bone (43 body weights (BW)·s⁻¹) in premenopausal women., Methods: Forty-seven premenopausal women (age, 39.2 ± 5.6 yr; mass, 65.9 ± 11.0 kg; height, 1.67 ± 0.06 m) performed walking (slow, fast, and with bag), floor sweeping, running (slow and fast), jumping (low, <5 cm; high, >5 cm), and box drop (20 cm) trials. Peak accelerations were sampled at 100 Hz by GENEActiv and ActiGraph GT3X+ accelerometers (ActiGraph LLC, Pensacola, FL) worn at the hip (vertical and resultant) and the wrist (resultant). A force plate (960 Hz, AMTI) was used to assess peak vertical GRF and peak loading rate for eight steps per activity. Receiver operating characteristic curves were used to determine the optimal peak acceleration cut-points associated with a loading rate of 43 BW·s⁻¹ in 37 participants, and these cut-points were cross-validated in the remaining 10 participants., Results: For all activities combined, peak accelerations were positively and significantly (P < 0.001) correlated with peak vertical GRF (hip r > 0.8, wrist r > 0.7) and peak loading rate (hip r > 0.7, wrist r > 0.57). Irrespective of monitor type and wear site, peak acceleration discriminated between loading rates above and below 43 BW·s⁻¹ with high levels of accuracy (area under the curve >0.92, P < 0.001). Overall classification agreement was >85% for both monitors worn at either the wrist or hip in the cross-validation sample., Conclusion: GENEActiv and ActiGraph GT3X+ accelerometers worn at the wrist or hip can be used as an unobtrusive tool to identify the occurrence of loading rates likely beneficial to bone in premenopausal women during their daily activity.

Integrated biomechanical and engineering assessments were used to determine how humans responded to variations in turf during running and turning. Ground reaction force (AMTI, 960 Hz) and kinematic data (Vicon Peak Motus, 120 Hz) were collected from eight participants during running (3.83 m/s) and turning (10 trials per condition) on three natural turf surfaces in the laboratory. Surface hardness (Clegg hammer) and shear strength (cruciform shear vane) were measured before and after participant testing. Peak loading rate during running was significantly higher (p < .05) on the least hard surface (sandy; 101.48 BW/s ± 23.3) compared with clay (84.67 BW/s ± 22.9). There were no significant differences in running kinematics. Compared with the "medium" condition, fifth MTP impact velocities during turning were significantly (RM-ANOVA, p < .05) lower on clay (resultant: 2.30 m/s [± 0.68] compared with 2.64 m/s [± 0.70]), which was significantly (p < .05) harder "after" and had the greatest shear strength both "before" and "after" participant testing. This unique finding suggests that further study of foot impact velocities are important to increase understanding of overuse injury mechanisms.

Research suggests that heightened impacts, altered joint movement patterns, and changes in friction coefficient from the use of artificial surfaces in sport increase the prevalence of overuse injuries. The purposes of this study were to (a) develop procedures to assess a tennis-specific movement, (b) characterize the ground reaction force (GRF) impact phases of the movement, and (c) assess human response during impact with changes in common playing surfaces. In relation to the third purpose it was hypothesized that surfaces with greatest mechanical cushioning would yield lower impact forces (PkFz) and rates of loading. Six shod volunteers performed 8 running forehand trials on each surface condition: baseline, carpet, acrylic, and artificial turf. Force plate (960 Hz) and kinematic data (120 Hz) were collected simultaneously for each trial. Running forehand foot plants are typically characterized by 3 peaks in vertical GRF prior to a foot-off peak. Group mean PkFz was significantly lower and peak braking force was significantly higher on the baseline surface compared with the other three test surfaces (p<0.05). No significant changes in initial kinematics were found to explain unexpected PkFz results. The baseline surface yielded a significantly higher coefficient of friction compared with the other three test surfaces (p<0.05). While the hypothesis is rejected, biomechanical analysis has revealed changes in surface type with regard to GRF variables.