Time to stability of treadmill running kinematics in novel footwear with different midsole thickness.

Running studies, particularly those examining footwear effects, commonly use warm-up or familiarization periods prior to testing. There is no consensus for how long these familiarization periods should be to ensure stable running kinematics prior to experimental testing in novel footwear. The aim of this study was to assess the time to stability of kinematic variables during treadmill running in novel compared to habitual neutral cushion footwear in distance runners. A cross-sectional analysis of 15 distance runners (seven women, eight men) during 10-minute treadmill running bouts in minimal, neutral cushion, and maximal cushioned footwear was conducted while lower extremity kinematics were recorded for 10 s at the end of each minute. Test-retest intra-class correlation coefficients (ICC, 3, k) were used to detect time to stability in cadence, vertical oscillation, peak dorsiflexion angle, peak eversion angle, and peak knee flexion angle. All kinematic variables were stabilized within two to three minutes (ICC < 0.90) and the type of novel footwear did not influence time to stability. These findings indicate that a two to three minute, ∼310-540 steps, depending on running cadence, familiarization period, regardless of footwear novelty, is sufficient for stabilization of these kinematic variables during treadmill running.

Joint work is not shifted proximally after a long run in rearfoot strike runners.

Distal-to-proximal redistribution of joint work occurs following exhaustive running in recreational but not competitive runners but the influence of a submaximal run on joint work is unknown. The purpose of this study was to assess if a long submaximal run produces a distal-to-proximal redistribution of positive joint work in well-trained runners. Thirteen rearfoot striking male runners (weekly distance: 72.6 ± 21.2 km) completed five running trials while three-dimensional kinematic and ground reaction force data were collected before and after a long submaximal treadmill run (19 ± 6 km). Joint kinetics were calculated from these data and percent contributions of joint work relative to total lower limb joint work were computed. Moderate reductions in absolute negative ankle work (p = 0.045, Cohen's d = 0.31), peak plantarflexor torque (p = 0.004, d = 0.34) and, peak negative ankle power (p = 0.005, d = 0.32) were observed following the long run. Positive ankle, knee and hip joint work were unchanged (p < 0.05) following the long run. These findings suggest no proximal shift in positive joint work in well-trained runners after a prolonged run. Runner population, running pace, distance, and relative intensity should be considered when examining changes in joint work following prolonged running.

Lower Limb Joint Kinetics During Walking in Middle-Aged Runners With Low or High Lifetime Running Exposure.

Aging is associated with a distal-to-proximal shift in joint kinetics during walking. This plasticity of gait is amplified rather than attenuated in old adults with high physical capacity. Because running is associated with greater kinetic demands at the ankle, older individuals with more versus less lifetime running exposure may retain a larger proportion of their ankle kinetics. The purpose of the study was to compare lower-extremity joint kinetics during walking between middle-aged runners with high and low lifetime running exposure. Eighteen middle-aged runners (9 per group) participated. Joint kinetics were calculated from kinematic and ground reaction force data during overground walking at 1.3 m·s-1 and compared between groups. High exposure runners produced 50% greater positive hip work (P = .03; Cohen d = 1.02) during walking compared with low exposure runners, but ankle kinetics were not different between groups. No other differences in joint kinetics or kinematics were observed between groups. These findings suggest that the age-related increase in hip joint kinetics during walking could be a compensatory gait strategy that is not attenuated by lifetime running exposure alone. Finally, the amount of lifetime running exposure did not affect ankle kinetics during walking in middle-aged runners.