Running performance and running economy can be quantified as the steady-state of oxygen consumption at a given running speed. Running economy can be influenced by long-term interventions such as resistance training and interval training.
Muscle and tendon stiffness does influence running performance, but there are two sides to the story. Evidence suggests a more compliant quadriceps tendon and aponeurosis is associated with better running economy in endurance athletes. On the other hand, stiffer tendons of the plantar flexors and stiffer muscle-tendon units of the hamstrings are also associated with better running economy.
What are the effects of a single bout of stretching on running economy and/or performance prior to an event? Evidence suggests that solely static stretching prior to a running event does not positively influence running performance or economy. If static stretching is applied for up to 90 seconds in combination with a warm-up, it does yield a 54% reduction in acute muscle injuries. Dynamic stretching for up to 220 seconds in total does however positively influence running performance, and targeted dynamic stretching (ie quadriceps where compliance is needed) does improve running economy.
It has been found that the less flexible runner should stretch more frequently than a more flexible athlete. This allows a more economical run as a result of improved joint range of motion.
Konrad, A. et al. (2021). The impact of a single stretching session on running performance and running economy: A scoping review. Frontiers in Physiology. 630282