Take Home Points
The larger and persistent KE strength losses observed under heat stress are associated with greater levels of central fatigue especially during sustained contractions.
Tennis is an intermittent activity interposed with short bouts (3–10 s) of high-intensity and light activity or rest (20–25 s) for a period of time (1–5 h) (Périard 2014). Repeating this high-intensity movement is noticeable by the development of fatigue and sub maximal performances. From a neuromuscular perspective, fatigue is defined as an exercise-induced decrement in the capacity to produce/maintain maximal force or power (Périard 2014). Fatigue is a complex topic, with contributions from the brain (central fatigue) and muscles (peripheral fatigue). Neuromuscular function decreases during and following (3 h) match-play tennis in different temperate conditions. It was shown that maximal strength of the knee extensors (KE) and plantar flexors (PF) decreases during short maximal voluntary isometric contractions (MVCs). This associates with a decrease in voluntary muscle activation (VA), adjustments in contractile function and the development of low-frequency fatigue, depending on the muscle group.
Périard (2014) analyzed the impairments in lower limb maximal strength and voluntary activation (VA) following match-play tennis in hot and cool conditions. Torque and VA were evaluated during brief (5 s) and sustained (20 s) maximal voluntary isometric contractions of the knee extensors (KE) and plantar flexors (PF) in 12 male tennis players before (pre) and after (post, 24 h and 48 h) ~115 min of play in hot (~37°C) and cool (~22°C) conditions.
The results note higher Rrectal temperature following play in hot than in cool (~39.2 vs ~38.5°C). Torque production decreased from pre match to post match during the brief and sustained contractions in hot (KE: ~22%; PF: ~13%) and cool (KE: ~9%, PF: ~7%). KE strength losses in hot were greater than in cool and persisted for 24 hours. Post-match brief and sustained KE VA was lower in hot than in cool, in which VA was maintained. PF VA was maintained throughout the protocol. Peak twitch torque and maximum rates of torque development and relaxation in the KE and PF were equally reduced post match relative to pre match in hot and cool conditions, and were restored near baseline within 24 h. Neuromuscular system integrity of the lower limbs is compromised immediately following match-play tennis in hot and cool conditions due to the development of peripheral fatigue. The larger and persistent KE strength losses observed under heat stress are associated with greater levels of central fatigue especially during sustained contractions.
This study has suggested that knee-extensor and plantar-flexor muscle strength is changed following match-play tennis in hot and cool conditions. This is due to significant levels of peripheral fatigue. In the knee-extensors, the loss of strength intensifies following play in the heat in association with larger reductions in central neural drive. This continues 24 hour into recovery when performing sustained contraction. These changes in neuromuscular system integrity have the potential to negatively influence the efficiency of on-court movements and stroke proficiency during match-play tennis, as well as in the recovery period (Périard 2014). Match-related physical performance may decrease during prolonged matches and tournament play, especially under heat stress. This can be caused by the progressive development of fatigue in large muscle groups, such as the quadriceps. Given the specific role of the knee-extensors and plantar-flexors in performing tennis movements and actions, fatigue in these muscle groups could impact tournament play.
Périard JD, Girard O, Racinais S. Neuromuscular adjustments of the knee extensors and plantar flexors following match-play tennis in the heat. Br J Sports Med. 2014 Apr;48 Suppl 1:i45-i51.
Written by Chris Barber, CPT