Recreational running has gained immense popularity in recent years. Improving a race performance or time is a motivating factor for a number of recreational runners. It has been proposed that running economy (RE), V̇O₂ₚₑₐₖ, fractional utilisation of V̇O₂ₚₑₐₖ, lactate threshold, and footwear all contribute to running performance. Footwear manufacturing company Nike, Inc. has developed the Nike Vaporfly (VP4) running shoe, shown to improve running economy in elite athletes by ~3 to 4%. No research has explored the effect of VP4 on recreational runners. The aims of this Thesis were to: (1) review articles focusing on running economy, race and time-trial performance, footwear, footstrike, and perception (Chapter One); (2) investigate the energetic cost and time-trial performance in male recreational runners wearing VP4, lightweight racing flats (FLATS), and their own habitual running shoes (OWN) (Chapter Two); (3) summarises the findings of this Thesis, discuss its strengths and limitations, and addresses future research directions (Chapter Three). In Chapter One, research on the relationship between RE, race and time-trial (TT) performance, footwear, footstrike, and perception in relation to running shoes was reviewed. Runners with a superior RE consume less oxygen and run faster than runners with an inferior RE. There is a positive correlation between V̇O₂ₚₑₐₖ, fractional utilisation, lactate threshold, and average race or TT performance. Footwear midsole compliance, resilience, longitudinal bending stiffness, and mass are all key characteristics linked with RE and running performance. Research appears to indicate that rearfoot runners potentially benefit more from wearing VP4 than non-rearfoot runners. Running shoe comfort, brand name, advertising, price, and previous experience all play a role in runners’ perception of running shoes. In Chapter Two, 18 male recreational runners (age: 33.5 ± 11.9 y, V ̇O₂ₚₑₐₖ: 55.8 ± 4.4 mL·kg⁻¹·min⁻¹) completed three sessions to assess their RE and 3-km TT performance in VP4, FLAT, and OWN in a randomised manner. Participants completed 3 x 3-minute bouts at 60%, 70%, and 80% of their V̇O₂ₚₑₐₖ speed, followed by a 3-km TT after a 5-minute rest. Footwear significantly affected RE variables across intensities (P < 0.002). Oxygen consumption was lower in VP4 (3.6 to 4.5%, P ≤ 0.002) and FLAT (2.4 to 4.0%, P ≤ 0.042) versus OWN across intensities, with a non-significant difference between VP4 and FLAT (1.0 to 1.6%, P ≥ 0.325). TT performance was superior in VP4 by 2.4% versus OWN (P = 0.005) and 1.8% versus FLAT (P = 0.032). Times between OWN and FLAT (0.5%, P = 0.747) were similar. Overall, VP4 improved lab-based RE measures in male recreational runners at relative speeds compared to OWN, but improvements in VP4 were not significant versus FLAT. More runners exhibited better treadmill TT performances in VP4 (61%) versus FLAT (22%) and OWN (17%). The variability in individual oxygen consumption (-3.1 to 12.1%) and TT (-3.8 to 8.2%) suggests individualised shoe responses. Chapter Three summaries the findings from Chapter Two. Overall, this Thesis provides evidence that the commercially available VP4 can improve RE and 3- km TT in most male recreational runners using laboratory-based data particularly when compared to OWN. FLAT were also effective in improving RE and enhancing TT performance in some runners, albeit fewer. There was considerable variability between runners and intensities, which support individual rather than generalised benefit of VP4 in recreational runners seeking to improve running performance. Investigating the biomechanical adaptation to VP4, as well as responses to footwear based on footstrike patterns, could shed light on mechanisms that contribute to improved running performance in recreational runners.