Final answer:
PNF stretching requires a partner or trainer to be effective. It involves both stretching and contracting the muscle groups gradually and should be done repeatedly throughout the week following a proper warm-up.
Step-by-step explanation:
PNF Stretching Requirements
For Proprioceptive Neuromuscular Facilitation (PNF) stretching to be effective, it must meet certain conditions. Contrary to quick movements, PNF stretching involves a gradual process that includes stretching and contracting the targeted muscle groups. It is also not a one-time weekly routine but is often recommended to be done several times a week for optimal results. It requires a partner or trainer to provide resistance against the muscle's contraction, which is an essential component of PNF stretching techniques. Lastly, an effective PNF stretching routine should follow a proper warm-up to prepare the muscles and reduce the risk of injury.
Therefore, the correct answer to the initial question is that PNF stretching requires a partner or trainer. Regarding warm-ups and injury prevention, although not the answer to the specific question, PNF stretching could play a role. The probability (P) an athlete stretches before exercising could be influenced by factors such as past injuries, and the likelihood of stretching given no injury in the last year might indicate a routine or preventative approach to their overall fitness strategy.