What differentiates rearfoot strike runners with low and high vertical load rates?

Cues to land softly and quietly result in acute reductions in ground reaction force loading rates in runners

BACKGROUND

A common gait retraining goal for runners is reducing vertical ground reaction force (GRF) loading rates (LRs), which have been associated with injury. Many gait retraining programs prioritize an internal focus of attention, despite evidence supporting an external focus of attention when a specific outcome is desired (e.g., LR reduction).

RESEARCH QUESTION

Does an external focus of attention (using cues for quiet, soft landings) result in comparable reductions in LRs to those achieved using a common internal focus (forefoot striking while barefoot)?

METHODS

This observational study included 37 injured runners (18 male; mean age 36 (14) years) at the OMITTED Running Center. Runners wore inertial measurement units over the distal-medial tibia while running on an instrumented treadmill at a self-selected speed. Data were collected for three conditions: 1) Shod-Control (wearing shoes, without cues); 2) Shod-Quiet (wearing shoes, cues for quiet, soft landings); and 3) Barefoot-FFS (barefoot, cues for forefoot strike (FFS)). Within-subject variables were compared across conditions: vertical instantaneous loading rate (LR, primary outcome); vertical stiffness during initial loading; peak vertical GRF; peak vertical tibial acceleration (TA); and cadence.

RESULTS

Vertical LR, stiffness, and TA were lower in the Shod-Quiet compared to Shod-Control p < 0.001). Peak vertical GRF and cadence were not different between Shod-Quiet and Shod-Control. Reductions in stiffness and LR were similar between Shod-Quiet and Barefoot-FFS, and GRF in Barefoot-FFS remained similar to both shod conditions. However, runners demonstrated additional reductions in TA and increased cadence when transitioning from Shod-Quiet to the Barefoot-FFS condition (p < 0.05).

SIGNIFICANCE

These results suggests that a focus on quiet, soft landings may be an effective gait retraining method for future research.

Effect of surface inclination on vertical loading rate and footstrike pattern in trail and road runners

Trail runners have been reported to be more injury prone than road runners. Limited past studies have examined the difference in the running biomechanics between the two groups of runners. More importantly, the effect of surface inclination has not been fully investigated. Hence, this study examined the effect of surface inclination on running biomechanics in trail and road runners. Twenty trails and 20 road runners were recruited in this study. Trail runners appeared to be more experienced and had longer training distance per week (p < 0.001) compared to road runners. All participants ran at a self-selected pace on an instrumented treadmill in three inclination conditions (i.e., level, +10% uphill and -10% downhill) in a random order. Vertical average loading rate (VALR), vertical instantaneous loading rate (VILR) and footstrike angle (FSA) were measured using established methods. Trail runners experienced greater VILR (p = 0.039, Cohen's d = 2.9) with a greater FSA (p = 0.002, Cohen's d = 1.1) during downhill running than road runners. No significant differences in VALR, VILR and FSA were found between the two groups during level and uphill running. Our findings provide potential biomechanical rationale to explain a higher injury incidence among trail runners.

Age differences in running biomechanics during footstrike between preschool children and adults

This study aimed to compare impact loading between two age groups of preschool children (3-4 and 5-6 years old) and one group of young adults representing mature level of running skill (n = 15 per group). Three-dimensional biomechanical data were collected during running barefoot, in minimalist and running shoes. A two-way mixed ANOVA was performed to assess age and footwear differences in vertical instantaneous loading rate (VILR). An interaction was found in VILR. Older (5-6) preschoolers had 30-31% lower VILR than younger (3-4) (p = 0.012, d = 1.02; p = 0.001, d = 1.18) and adults had 51-77% lower VILR than younger preschoolers (p = 0.001, d = 1.85; p = 0.001, d = 2.82) in minimalist and running shoes, respectively. Additionally, adults had lower VILR than older preschoolers in running shoes (p = 0.001, d = 2.68). No differences were found between older children and adults in barefoot and minimalist shoes. Loading decreased with increasing age, particularly in minimalist and running shoes. Unchanged cadence and running speed did not explain the decrease of VILR during preschool age. The explanation likely underlies in lower limb alignment during footstrike and developmental ontogenetic changes.