Why do some people respond better to advanced footwear technology, but others do not?

This is a randomised crossover trial with repeated measures performed in a laboratory. Participants will be required to attend two sessions within a week, where each session should be around 90 to 120 minutes each. The aim of the study is two fold: 1) identify whether intrinsic variables (namely participant characteristics, plantarflexion function, and running biomechanics) contribute to running economy responses in advanced footwear technology. Second, we aim to identify whether plantarflexion fatigue influences the running economy responses to advanced footwear technology. Session one. After informed consent and baseline data collection (height, mass, running participation, injury history, own shoe characteristics), participants will complete a series of standardised assessments: These measurements include: baseline information like age, height, mass, and running experience; foot width, foot length, and foot height while standing and sitting; Achilles tendon moment arm length and plantarflexion gear ratio; Foot Posture Index 6; triceps surae muscle, plantar fascia, and Achilles tendon stiffness; 1st metatarsophalangeal joint range of motion in standing; plantarflexion isometric strength in standing and sitting, weighted power, and strength-endurance; ankle inversion, ankle eversion, and toe flexor isometric strength; vertical hopping stiffness; and VO2peak running on a treadmill in their own shoes. The incremental VO2peak test will be conducted at the end of the session running on a treadmill using an incremental speed protocol. The starting speed will be individualised in the aim to have the test finish within 10-15 minutes. The VO2peak test will set the speed for running during the main intervention: running in a control and running in a shoe with advanced footwear technology in session 2. Session 2 is the main experimental session as running economy tests will be performed in an advanced footwear technology (AFT) shoe (Salomon S/Lab Phantasm 2) and a control shoe (Salomon Aero Glide 2). These data will be used to determine the running economy responses of runners to advance footwear technology. After rating their perceived calf muscle soreness and fatigue on 100 mm visual analog scale (VAS), participants will warm up for 6 minutes running on a treadmill in their own shoes at a self-selected speed for the first 3 minutes and at 70% of the speed founf to elicit VO2peak for the last 3 minutes. Participants will complete shoe visual analogue scale measures and baseline lactate will be recorded. Baseline weighted plantarflexion power will be assessed. Participants will then complete 4x 6 minute running economy tests using the experimental shoes. The ordering of the shoes used will be either AFT, Control, Control, AFT or Control, AFT, AFT, Control. Running speed on the treadmill will be 70% of the speed found to elicit VO2max in session 1. During each running trial, footstrike patterns and contact and flight time from the right leg will be gathered from 30 seconds of running in the last minute. After each running economy trial, perceptual readings of comfort and running experience, we well as lactate, will be collected while sitting down with shoes removed. Runners will have 5 minutes seated rest between economy trials. To identify whether plantarflexion fatigue influences running economy responses to AFT, the plantarflexors will be fatigued using dynamic tasks the same day, immediately following the last 5 minutes rest period of the running economy trials. Weighted plantarflexion power will be assessed first (5 seconds), and then participants will complete as many repetitions as possible of concentric-eccentric plantarflexion repetitions on a 10 degree incline (i.e., calf raise test) on the non-dominant and dominant legs until failure. Participants will complete another round of repetitions to fatigue with an additional 30% body mass load until failure, and weighted plantarflexion power will be re-assessed as measure of fatigue. Participants will rate their perceive calf soreness and fatigue on a 100 mm VAS. and participants will complete a further 1x6 minute running economy test immediately after shoes are replaced, either in the order of AFT, Control or Control, AFT. After the first running economy test, the plantarflexion fatiguing procedures will be repeated immediately after lactate recording from the running economy test before assessment of running economy a second time. A final weighted plantarflexion power test will be conducted after the running trial on the dominant leg only. To assess adherence to the fatigue intervention, videos of the foot will be recorded to determine how many repetitions are completed during the fatigue test. Furthermore, visual analogue scales on perceived soreness and fatigue will be used to monitor reaching subjective perceptions of fatigue. The weighted power test is completed before and after the fatiguing protocol to quantify the level of dynamic fatigue.