(15) A MULTI-MONTH WILDERNESS BACKPACKING TREK IMPACTS LOWER LIMB NEUROMUSCULAR FUNCTION: A CASE STUDY

Purpose: Observe the consequences of a multi-month, self-supported thru-hiking trek in the wilderness on lower extremity motor control and performance. 

Methods: An experienced backpacker (30.1yrs; 78.3kg; 179.1cm; 20.5% BF; 35.2kg SMM) completed a wilderness-based backpacking trek known as the Appalachian National Scenic Trail northbound thru-hike.  The participant hiked 3,531km with an accumulated elevation gain of 99,643m over 139 days.  Lower body mobility, motor control, and isometric force production data were collected at 4 time points (PRE-, MID-, POST-, and 1-WK-POST) surrounding the thru-hike expedition.  Motor control, symmetry, and mobility of the lower limbs were assessed via the lower quarter Y-balance test (LQYBT). As part of the LQYBT, leg length (LL) was measured from the anterior superior iliac spine (ASIS) to the medial malleolus. The LQYBT requires the participant to maintain single leg stance while reaching their non-stance foot in the anterior (ANT), posterolateral (PTL), and posteromedial (PTM) directions. An isometric mid-thigh pull (IMTP) with a bilateral force plate was used to determine maximal isometric force production and discriminate unilateral contribution.  LQYBT statistical analysis included normalizing composite (NCOMP) scores ((ANT+PTM+PTL/limb length*3)*100) across the 4 time points. Data are reported as percent changes from the pre-trek baseline (PRE).

Results: Left stance (LS) NCOMP scores declined in response to initial trek demands (PRE 96.26cm; MID 89.35cm, Δ-7.18%) and were maintained through trek end and initial recovery (POST 89.54cm, Δ-6.98%; 1-WK-POST 86.18cm, Δ-10.47%). Right stance (RS) performance expressed a more dramatic NCOMP decay pattern (PRE 89.87cm; MID 79.58cm, Δ-11.45%; POST 79.05cm, Δ-12.04%; 1-WK-POST 81.59cm, Δ-9.21%). Left-right (L/R) NCOMP difference expanded with trek duration (PRE 6.39cm; MID 9.77cm, Δ52.90%; POST 10.49cm, Δ64.19%) that improved with non-active recovery (1-WK-POST 4.58cm, Δ-28.28%). LL discrepancy (LLD) increased dramatically (PRE 0.10cm; MID 1.00cm, Δ900.0%; POST 2.10cm, Δ2000.0%) in response to trek demands favoring a rightward shift that did not completely normalize by 1-WK-POST (1.00cm, Δ900.0%). Unilateral force application dominance reversed from left to right over the trek (PRE 121.50N; MID 30.50N, Δ-74.90%; POST -110.00N, Δ-190.53%) and failed to return to baseline 1-WK-POST (-49.00N, Δ-140.33%).

Conclusion: 139-d of self-supported thru-hiking greatly impacts lower body movement capacity, reducing motor control and balance in favor of stability. NCOMP reach distance and NCOMP L/R difference both failed to meet established standards ( >94% LL*3, < 4cm L/R diff) after PRE, if at all, which increases injury risk 6.5x (Plisky et al., 2006; Gonell et al., 2015). Pelvic lateral tilt imbalance (via LLD) was also exacerbated by hiking distance and loading demands. Motor control limitations and pelvic position changes seemed to impact unilateral force application. With sedentary rest, the body began reverting to the previously established neuromuscular performance baseline, but 1-WK proved to be a suboptimal recovery timeline.  PRACTICAL APPLICATION: To minimize injury risk and event dropout, LQYBT and LL measures should be used as pre-trek screening tools to identify motor control and movement discrepancies contributing to force profile imbalances likely to be exacerbated by compounding physical activity density.

Acknowledgements: None