Background: Hip and knee flexion joint motions are frequently examined in clinical practice using camera based motion capture (CBMC) systems; however, these systems require elaborate setups and dedicated space. Inertial measurement unit (IMU) based systems avoid these disadvantages but require validation before widespread adoption. Moreover, it is important for clinical practice to determine the stability of these systems for prolonged evaluation periods. The purpose of this study was to assess the validity of a three-sensor inertial measurement unit system for calculating hip and knee flexion angles during gait by comparing with a gold standard CBMC system. Validity was also examined before and after a treadmill walking session. Methods: Twenty healthy participants were tested. Twenty seconds of gait at preferred walking speed were analyzed before and after thirty-two minutes of treadmill walking using previously validated CBMC methods and with a custom IMU model. Measurement validity for the IMU system was evaluated using Bland & Altman 95 percent limits of agreement, linear regression, mean absolute error and root mean square error. The effects of a measurement zeroing calibration strategy were also investigated. Results: Strong measurement agreement was observed for both hip and knee flexion angles, although overall agreement for the hip exceeded that for the knee. Linear regressions between the datasets for each participant illustrated strong (> 0.94) relationships between IMU and CBMC measurements. More significant changes between timepoints were observed for the knee than for the hip. Error values were generally reduced when zeroing calibration was implemented. Conclusion: The IMU system presented in this study is a convenient and accessible technique to measure joint angles. The protocol described in the current study can be easily applied in the clinical setting for evaluation of clinical populations. Additional development work on sensor placement and calibration methods may further increase the accuracy of such methods.

The ability to meet high exercise intensities is limited by the increased risk of injury in some clinical populations. Previous studies have linked large tibia peak positive accelerations resulting from running to increased risk of developing lower-extremity injury. The purpose of this study is to determine the feasibility of using a hip flexion feedback system (HFFS) to meet and maintain different exercise intensities while maintaining low tibia axial accelerations. Ten healthy participants were tested on a HFFS test and an independent walking/running test to meet exercise intensities of 40% and 60% of heart rate reserve (HRR). During the HFFS test, the HFFS controlled in real time the exercise intensity by directing individuals to specific maximum hip flexion targets during walking and providing visual information that assists them in maintaining low tibia peak positive accelerations during the initial contact phase. Maximum hip flexion targets during walking are calculated based on real-time readings of the participant’s heart rate. During the independent test, exercise intensity was controlled independently by the participant using treadmill speed. Compared to the independent test, using the HFFS at 60% HRR resulted in similar heart-rate error but lower tibia peak positive accelerations. No differences were observed for the 40% HRR intensity. This paper describes a novel exercise approach that uses the individual’s heart rate to calculate maximal hip flexion targets that an individual should meet during treadmill walking. The HFFS also provides tibia peak positive peak acceleration cues. Therefore, the HFFS can increase and control exercise intensities while maintaining low tibia accelerations. In particular, the HFFS might be an alternative strategy to meet moderate to vigorous exercise intensities in populations at risk of developing lower-extremity injuries.

Background: Increased hip-flexion gait (HFgait) has been shown to promote increased aerobic demands by increasing peak swing-phase hip-flexion angles while walking at comfortable speeds. Biomechanically, HFgait produces a gait pattern similar to walking, while removing the flight phase from running and reducing tibial accelerations. We sought to identify knee joint contact forces between HFgait and common exercise modalities, including running, walking, and cycling, across intensity levels. Methods: Ten healthy participants completed two bouts (low and high intensity) of four different exercises: treadmill running, walking, HFgait, and cycling. Tibiofemoral joint compressive force (TCF) was estimated using a static optimization-based approach. Results: Peak TCF was greater in running compared to HFgait, walking, and cycling; greater in HFgait compared to cycling; and greater in walking compared to cycling. The integral of TCF (iTCF) was greater in running compared to cycling, greater in HFgait compared to running, walking, and cycling, and greater in walking compared to running and cycling. Conclusions: HFgait produced lower knee joint loading than running, comparable joint loading to walking, and greater joint loading than cycling. Thus, HFgait may serve as an exercise modality for populations where joint loading is of particular concern, while achieving aerobic demands similar to running or increased functional demands compared to stationary cycling.

Background: Previous research has shown that increasing cycling cadence can result in improved post-cycling gait velocity. However, the specific threshold of cycling cadence required to bring about clinically meaningful changes in gait velocity remains unknown. This study aimed to determine the minimum increment in cycling cadence that would lead to a significant improvement in post-cycling gait velocity. Methods: A total of 42 young adults participated in our study and were randomly assigned to one of three groups: TEN, TWENTY, and THIRTY. Each group was assigned to cycle at a cadence at the corresponding percentage higher than the participant’s self-selected gait cadence. Each participant engaged in a 15-min cycling session at their respective assigned cycling cadence. Before and after cycling, participants completed a 10-meter walk test while spatiotemporal parameters of gait, ground reaction forces, lower extremity kinematics, and kinetics were recorded. Results: One-way ANOVA revealed no statistically significant changes in spatiotemporal, ground reaction force, kinematics, and kinetics variables pre- and post-cycling. However, there were both statistically significant (F(2,41) = 3.794, p = 0.031, η² = 0.604) and clinically meaningful changes (0.07 m/s) in post-cycling gait velocity in the THIRTY group only. Conclusions: This suggests that a cycling cadence of 30% or higher is the minimum requirement to produce a clinically significant improvement in gait velocity.