Trail running performance and biomechanics: insights to support innovative off-road footwear development

The analysis of trail running performance has gained increasing attention in recent years, as trail running has specific energetic, biomechanical and neuromuscular demands that differ from those of traditional road running. Steep uphill and downhill sections, irregular and unstable ground, and prolonged race durations require athletes to continuously adjust their movement patterns and to tolerate high eccentric loads and cumulative fatigue. However, most of the available knowledge on running comes from level, even-surface conditions, and classical laboratory tests only partially capture the complexity of trail running. Field studies, in turn, often lack detailed control over speed, stride mechanics and terrain properties, making it difficult to isolate the mechanisms underlying performance. For these reasons, there is a need for an integrated approach combining controlled experimentation and ecologically valid race data, with a particular focus on uneven terrain, uphill and downhill segments, sex differences and fatigue-related performance decline (durability). The present thesis was designed within this framework, keeping trail running as the common denominator and addressing its demands from complementary physiological, biomechanical and neuromuscular perspectives. Chapter 1 provides the general background on trail running, outlines the specific constraints imposed by uphill, downhill and uneven surfaces, and summarises current evidence on performance determinants in off-road running, as well as the overall aims and hypotheses of the thesis. Chapter 2 examines the effects of uneven terrain under highly standardised conditions, constraining speed, step frequency and foot placement to investigate how surface irregularity influences the cost of running and lower-limb muscle activation, with a focus on ankle stabiliser muscles. Chapter 3 analyses kinematics and performance in uphill and downhill sections during a Skyrunning race in well-trained and elite male athletes, quantifying the relative importance of ascent and descent to overall race outcome and describing how spatiotemporal parameters differ across performance levels and evolve with fatigue. Chapter 4 addresses sex differences in competitive trail running, comparing female athletes with male counterparts matched for either relative or absolute performance to identify sex-related differences in uphill and downhill performance and running kinematics, and to assess how these differences change after controlling for 5 speed. Chapter 5 investigates the effects of manipulating downhill stride frequency on neuromuscular fatigue, subsequent uphill performance and durability in well-trained and elite trail runners, using an uphill–downhill–uphill protocol to compare preferred versus increased stride frequency during a prolonged steep descent and to explore cardiometabolic decoupling as a marker of durability. Chapter 6 reports the applied work carried out with Treré Innovation, where different trail shoe prototypes were tested to explore how shoe design may influence running biomechanics, comfort and performance in off-road conditions. Chapter 7 presents an exploratory project conducted during an international research stay, where race-to-race performance variability and predictability are explored using a database of elite trail running results from multiple competitions. Finally, Chapter 8 presents a general discussion of the main findings, addresses the principal limitations of the work and proposes future directions for research on trail running performance and durability.