A Multiphase Analysis of Next-generation Trail Footwear (NEXTGENTRAIL)

Trail running involves substantial variations in terrain, gradient, and surface characteristics, creating physiological and biomechanical demands that differ from road running. Footwear may influence these responses through characteristics such as midsole foam properties, cushioning, and stack height. However, evidence regarding advanced footwear technology in trail running remains limited, particularly regarding whether laboratory findings translate to real-world trail conditions and whether footwear characteristics influence the maintenance of running performance during prolonged exercise.

The objective of this study is to investigate the effects of different advanced-foam trail-running footwear configurations on running economy, performance, comfort, biomechanical responses, and fatigue under laboratory and field-based trail-running conditions. The study will also examine whether footwear configuration influences durability, defined in this project as the maintenance of running economy and physiological efficiency during prolonged exercise.

The study will recruit approximately 30 competitive trail runners with experience in technical trail running who have been free from musculoskeletal injury for at least six months. Written informed consent will be obtained from all participants.

The study will use a two-phase experimental design.

In Phase 1, participants will be evaluated under three footwear conditions in randomized order:

1. High-stack advanced-foam shoe prototype: approximately 38.5 mm stack height, 6-mm drop, and 220 g.
2. Medium-stack advanced-foam shoe prototype: approximately 28.5 mm stack height, 6-mm drop, and 180 g.
3. Conventional-foam footwear: approximately 31.5 mm stack height, 6-mm drop, and 300 g.

If necessary, shoe mass will be standardized by adding weight to the lighter footwear configurations to help isolate the effects of foam characteristics.

Laboratory running economy will be assessed using 5-minute running trials under uphill and downhill conditions. Uphill running will be performed at 8 km/h with a 6% positive slope, and downhill running at 16 km/h with a 6% negative slope. Oxygen uptake and carbon dioxide output will be measured breath-by-breath using a metabolic gas analysis system. Biomechanical variables will also be recorded, including step frequency and ground contact time.

Following the laboratory assessment, participants will complete field-based running economy trials on a real trail surface. Each footwear condition will be tested in randomized order during 5-minute running trials at a controlled speed of 12 km/h. Speed will be controlled using acoustic signals. Oxygen consumption and carbon dioxide production will be measured using a portable metabolic system, while spatiotemporal gait variables will be recorded using an inertial measurement device. Participants will subsequently complete a short time trial to establish a representative running pace for the subsequent durability assessment.

In Phase 2, participants will complete prolonged trail-running sessions using the two advanced-foam footwear configurations. Each footwear condition will be assessed during a separate visit. The sessions will consist of repeated running on a 15-km trail course comprising five 3-km loops and approximately 375 m of elevation gain. Running intensity will be based on the pace obtained during the Phase 1 time trial, according to the final study protocol.

Running economy will be assessed repeatedly during the prolonged exercise sessions using portable metabolic measurements. Changes in physiological efficiency and fatigue will be evaluated across the running session. GPS-based measurements will also be collected to monitor pacing and changes in running performance.

The main physiological outcome is running economy, assessed through oxygen consumption and energy cost relative to running speed. Additional physiological, biomechanical, and perceptual outcomes include heart rate, step frequency, step length, ground contact time, rating of perceived exertion, perceived comfort, perceived performance, and pacing-related measures.

The study is designed to determine whether footwear-related differences in running economy identified under controlled laboratory conditions are maintained during real-world trail running. It will also investigate whether advanced-foam footwear configurations influence the deterioration of running economy and fatigue during prolonged trail-running exercise. The findings are intended to contribute to the scientific understanding of interactions between trail-running footwear, biomechanics, physiological responses, and endurance performance.