Dostan, A. | Search bioRxiv

bioRxiv2026

Edge-First Ground Reaction Force Estimation with Consumer Smartwatches

Ground reaction force (GRF) measurement remains largely confined to instrumented laboratories, limiting longitudinal monitoring in daily life. This article presents an edge-first wearable system for estimating vertical GRF from consumer smartwatches. Two Apple Watch Series 6 devices worn at the wrist and waist stream 12-channel inertial data at 100 Hz to an iPhone, where preprocessing, storage, and inference occur locally without cloud dependence. The proposed GRFNet-MultiScale model is a compact temporal convolutional network with four dilated residual blocks and a global context branch. Under leave-one-subject-out evaluation on 539 stance windows from 10 healthy participants, the dual-sensor system achieved a mean Pearson correlation of 0.798 with an RMSE of 257 N, while a wrist-only configuration retained 82.5% of dual-sensor correlation. Temporal attribution remained stable across validation folds and identified early-stance wrist acceleration as the dominant reproducible signal. The system is strongest for cyclic locomotion.

bioengineering↗

bioRxiv2025

A biomechanical investigation of stair descent in postmenopausal women: A regression analysis considering walking speed and T-score

IntroductionPrevious studies have examined gait biomechanics during stair descent in older adults, but limited evidence exists on how bone mineral density (BMD) influences these mechanics in postmenopausal women, a group at increased risk of falls and fractures. This study investigated the relationship between self-selected stair descent speed and femoral neck BMD (T-score) with gait biomechanical parameters in postmenopausal women across a wide range of T-scores, from normal to osteoporotic. MethodsForty-five postmenopausal women (mean {+/-} SD age: 67.3 {+/-} 1.5 years) descended a five-step, custom-built staircase at a self-selected speed, without using handrails. Three-dimensional kinematics and ground reaction force (GRF) data were collected using motion capture and force plates. Multiple linear regression models assessed how stair descent speed and femoral neck T-score influenced stair descent gait parameters. ResultsThe participants mean stair descent speed was 0.80 {+/-} 0.21 m{middle dot}s-{superscript 1}. Speed significantly explained variance in temporal-spatial, kinematic, GRF, joint moment, and joint power parameters (R{superscript 2} = 7% to 49%, P [≤] 0.01). The inclusion of femoral neck T-score in the regression models further improved the explanatory power of the model in anterior pelvic tilt (R{superscript 2} = 21%, P [≤] 0.01), hip adduction (R{superscript 2} = 11%, P [≤] 0.01), hip extension (R{superscript 2} = 29%, P [≤] 0.01), knee flexion (R{superscript 2} = 21%, P [≤] 0.01), ankle dorsiflexion (R{superscript 2} = 19%, P [≤] 0.001), mid-stance vertical GRF (R{superscript 2} = 20%, P [≤] 0.01) during the forward continuance phase, and the second vertical GRF peak (R{superscript 2} = 15%, P [≤] 0.01). ConclusionThis study demonstrates that stair descent speed and femoral neck T-score significantly influence lower limb biomechanics, accounting for up to 29% of the variance in key variables, particularly during the controlled lowering phase. Postmenopausal women with low BMD adopted altered movement strategies, such as increased frontal plane motion at the hip and pelvis, which may serve to maintain balance but could also elevate the risk of falls. The substantial eccentric muscle demands during stair descent contribute to mechanical loading of the lower limb skeleton, underscoring its potential not only as a complex functional task but also as an osteogenic stimulus. These findings highlight the value of targeted interventions aimed at improving eccentric strength and trunk control to enhance stair negotiation safety and support both musculoskeletal function and bone health in individuals with low BMD.

physiology↗