Battery lifetime continues to be a top complaint about smart phones. Dynamic voltage and frequency scaling (DVFS) has existed for mobile device CPUs for some time, and provides a trade off between energy and performance. Dynamic frequency scaling is beginning to be applied to memory as well to make more energy-performance tradeoffs possible. We present the first characterization of the behavior of the optimal frequency settings of workloads running both, under energy constraints and on systems capable of CPU DVFS and memory DFS, an environment representative of next-generation mobile devices. Our results show that continuously using the optimal frequency settings results in a large number of frequency transitions which end up hurting performance. However, by permitting a small loss in performance, transition overhead can be reduced and end-to-end performance and energy consumption improved. We introduce the idea of inefficiency as a way of constraining task energy consumption relative to the most energy-efficient settings, and characterize the performance of multiple workloads running under different inefficiency settings. Overall our results have multiple implications for next-generation mobile devices exposing multiple energy-performance tradeoffs.

Core stability is considered critical for the successful execution of rehabilitative and athletic tasks. While no consensus definition exists, different components related to core stability have been identified. An important component is the domain of motor control. There are few clinical tests assessing the motor control component of core stability (MCCS). To evaluate the interrater reliability and known-groups validity of a novel test of MCCS, the in-line half-kneeling test. The test is aimed at assessing MCCS by challenging the ability to maintain a static position with minimized contributions from the distal extremities over a minimized base of support. Cross-sectional group comparison study. Laboratory. 75 participants (25 individuals with a history of anterior cruciate ligament reconstruction, 25 uninjured Division 1 collegiate athletes, and 25 uninjured controls) were recruited from a university community. Participants were video recorded while performing the in-line half-kneeling test for 120 seconds bilaterally. Three observers independently viewed each video to determine if individuals broke form during each test using 2 dichotomous criteria. Cohen’s Kappa was used to assess interrater reliability, and Chi Square tests of independence were used to compare break rates between groups. Good-excellent interrater reliability (0.732 – 0.973) was seen between the 3 observers. Chi Square tests of independence revealed different break rates between all 3 groups. Compared to break rate for the reference control group (11/25 – 44%), those with a history of anterior cruciate ligament reconstruction broke at a higher rate (18/25 - 72%), while the uninjured collegiate athletes broke at a lower rate (4/25 - 16%). The in-line half-kneeling test is a reliable test between raters that can differentiate between groups expected to differ in MCCS.

Asymmetries are common during squats following anterior cruciate ligament reconstruction (ACLR). This study examined interlimb loading differences between squat phases at 6 months post-ACLR. Thirty-five participants performed bodyweight squats at self-selected speed and were analyzed using 3D motion capture. Vertical ground reaction force impulse (vGRFi), external knee flexion moment impulse (KFMi) and hip-to-knee flexion moment impulse ratio (HKRi) were calculated, along with interlimb ratios (ILR). Squat phase durations were also recorded. Paired t-tests and ANCOVA (controlling for time) were used to compare biomechanical variables across squat phases. Greater asymmetry was observed during ascent for vGRFi ILR (p = 0.045), KFMi ILR (p < 0.001) and HKRi ILR (p = 0.006). The ascent phase was faster than descent (p = 0.036). After adjusting for time, phase-related differences in ILRs were no longer significant. These findings suggest that greater limb and knee-specific loading asymmetries occur during the ascent phase of squats but may be influenced by movement speed. Importantly, significant knee-specific loading asymmetries persisted regardless of squat phase. At 6 months post-ACLR, addressing neuromuscular control and movement speed during rehabilitation may help reduce biomechanical imbalances during closed kinetic chain exercises.