Cooling

Cooling has been suggested to have a number of effects, including decreased muscle temperature, muscle damage and postexercise inflammation,12 reduced heart rate and cardiac output,13 peripheral vasoconstriction and reduced peripheral oedema formation12^–14 and analgesic effects.15 The actual mechanisms underlying the potential benefits of cooling interventions are still unclear.16 The effects of cooling on recovery have been reported to be larger for weight-bearing sports (ie, eccentric exercise) than for non-weight-bearing sports (cycling, swimming).17 Although no gold standard temperature protocol has been established, a typical recommendation by multiple researchers and practitioners is to cool the water to 10–15°C.17 ,18 In a meta-analysis of 21 studies (using a range of 5–15°C), the average improvement in performance measures (endurance, strength, sprint and jump activities) were 2–3%.19 A 2–3% improvement in tennis performance can significantly aid an athlete during a tournament, but also can help in the day-to-day improvements during practice. The higher the level of competition, the more important this small improvement becomes. Although many different cooling methods exist, the best outcomes have been found with cold water immersion techniques (typically between 5°C and 15°C19) over other forms of cooling (ice packs, ice vests, ice towels, etc).19 Immersion is a highly efficient method of cooling and decreases body core temperature at a rate of 0.15–0.35°C/min.20 ,21

In addition to temperature changes in muscle, another mechanism to explain the possible benefit of cooling on postexercise recovery is the effect of hydrostatic pressure.22 Hydrostatic pressure increases cutaneous interstitial pressure, causing a fluid shift from the interstitial to the intravascular space,23 which may reduce oedema and possibly secondary tissue damage.22 This process also increases intracellular–intravascular osmotic gradients, enhancing the clearance of waste products and possibly improving muscle contractile function.24 ,25 The increase in hydrostatic pressure results in a rise of central blood volume and cardiac output,26 increasing blood flow and the clearance of waste products. It is interesting to note that these responses increase as the depth of water immersion increases.22 Cooling packs or cooling vests have not shown benefits for recovery parameters, possibly because the body area cooled was too small to elicit hydrostatic pressure changes.19

A rather new whole body cooling technique, called a cryogenic chamber, is becoming more popular as a recovery tool for competitive athletes. Studies have investigated the influence of two sets of 3 min in a cryochamber (−110°C) at 24 and 26 h postexercise27 or three sets of 3 min in a cryochamber (−110°C) immediately postexercise and 24 and 48 h postexercise.28 These two studies showed vast differences in recovery measures. Cryotherapy performed 24 h after exercise was ineffective in alleviating muscle soreness or enhancing muscle force recovery,27 whereas when cryotherapy was started immediately postexercise28 improvements were found. The delay in cryotherapy by 24 h may have reduced the ability to improve recovery metrics. Although limited studies currently exist on cryotherapy chambers, and significantly more research is needed in this area, the use of −110°C chambers in short durations (∼3 min) immediately postexercise may have some positive effects on recovery.19 In an interesting study in tennis using this modality, 5 days of whole-body cryotherapy chamber exposure in conjunction with moderate-intensity training considerably improved the blood cytokine profile and physical performance of professional tennis players (ATP ranked between 150 and 900).29 However, cryotherapy chambers are significantly more costly than cold water immersion treatments and more data comparing the two methods are needed to determine if any greater benefits in recovery may be achieved.

Timing

Tennis requires athletes to perform multiple matches or practices in a single day. Some research has investigated the influence of cooling techniques used between these types of activities. If recovery time is less than 60 min the benefits of cooling techniques are suggested to be less about recovery and more related to precooling for the next exercise bout.17 When 2–3 h of recovery time is allowed between exercise bouts only negligible effects of cooling on performance have been found. It is interesting to note that cold water immersion techniques may be more effective the longer the timeframe between bouts. In a meta-analysis,30 the authors concluded that the largest effects of cooling on recovery can be expected 2–4 days after exercise.19 Effects of cooling were larger when repeatedly applied (usually once per day), so from a practical perspective, it has been suggested that cooling should take place immediately after exercise, and also on a daily basis following strenuous exercise.17

Hot water immersion

Throughout history, warm and hot water treatments have been used for muscle relaxation after physical exertion. Immersion of the body in 34–36°C water results in marked changes in the circulatory, pulmonary, renal and musculoskeletal systems as a result of increased hydrostatic pressures.11 ,22 The effects have been shown to be most pronounced for whole body (head out) immersion rather than partial immersion as increased pressure is proportional to the size of the immersed body surface area parts. Some studies have attempted to evaluate the influence of warm or hot water immersion of whole body24 ,31 or legs only32 on postexercise recovery. The legs-only immersion study found negligible effects on recovery parameters and were inferior compared with whole body immersion. Although hot water immersion showed benefits for whole body immersion, these benefits were inferior for recovery compared with cold water immersion. Alternating from cool to warm water immersion can accelerate clearance of blood lactate33 ,34 and creatine kinase.35

Rehydration

During tennis play, metabolic heat production from exercise and heat gain from the environment cause an increase in body core temperature. Consequently, fluid loss through sweating occurs to dissipate body heat and regulate core temperature. Sweating rates in tennis players have been reported to range from less than 0.5 to over 2.5 L/h.53 ,54 The composition of sweat includes electrolytes, particularly sodium, which ranges from approximately 20–80 mEq/L of sweat.53 The wide range in sweating rates and sweat sodium concentration among players is due to differences in genetics, maturation, body size, training/match intensity, environmental conditions and/or heat acclimatisation status. When fluid intake is less than sweat loss, a body water deficit, or dehydration, occurs. There is a paucity of data regarding the effect of hypohydration on tennis-specific performance. However, hypohydration has been found to impair aerobic performance, postural balance,55 cognitive performance, mood and mental readiness,56 ,57 which are all important components of tennis performance. Although some individuals may be more or less sensitive to hypohydration, the level needed to induce performance degradations approximates >2% decrease in body mass56 ,57 There is also evidence that further body water deficits result in further deteriorations in sport/exercise performance.56 ,58 ,59 Competitive tennis is typically played in warm-hot environments. Thus, it is important to note that the detrimental effect of hypohydration on aerobic performance is exacerbated when combined with heat stress.56 Furthermore, hypohydration impairs the body's heat dissipating mechanisms (ie, skin blood flow and sweating), leading to increased core temperature and risk of heat illness.56 Therefore, fluid replacement to ameliorate the deterioration in physiological function and performance that accompanies hypohydration is an important aspect of recovery from tennis play.

It is critical that fluid intake is customised for each individual's hydration needs. Body mass assessments can be used to gauge a player's sweat loss following a workout. Acute body mass change (eg, from before to after <3 h training) represents approximately 1 L of water loss per 1 kg of body mass loss.60 To achieve rapid and complete rehydration, it has been recommended for athletes to drink ∼1–1.5 L of a sodium-containing (20–50 mEq/L) fluid for each kg of body mass lost.56 ,57 ,61 The ingestion of sodium with a fluid replacement beverage helps stimulate more complete rehydration, including better plasma volume restoration and whole body fluid balance compared with ingestion of plain water.62^–65 The increase in serum sodium concentration and osmolality with sodium ingestion stimulates renal water reabsorption, as urine output is inversely related to the sodium content of the ingested fluid.63 Providing a chilled beverage with the addition of flavour and sweetness can improve beverage palatability and voluntary fluid intake.56

Carbohydrate

Owing to the stop-and-go nature of the sport, tennis players use a combination of anaerobic and aerobic energy systems, both of which rely on carbohydrate as the primary fuel source. Tennis practices/matches, especially those of longer duration and intensity, likely decrease glycogen stores. Therefore, carbohydrate intake to replenish liver and muscle glycogen before the next training session/match is an important aspect of recovery for the tennis player.66

The recommendations for carbohydrate intake during recovery are dependent on training/competition demands. When there is less than 8 h of recovery between practices or matches, experts recommend 1.0–1.2 g carbohydrate/kg immediately after the first session. This carbohydrate intake rate should be repeated every hour for 4 h.67 ,68 The timing of carbohydrate intake is especially important if the athlete has two practices or matches in 1 day. However, if there are one or more days between intense training sessions, the timing for glycogen replenishment is less urgent, provided sufficient carbohydrates are consumed during 24 h after the practice or match.69 Daily needs for carbohydrate fuel to support recovery and replenish muscle and liver glycogen stores (ie, in 24 h between tennis play) is 5–7 g carbohydrate/kg/day for moderate training (∼1 h/day) or 6–10 g carbohydrate/kg/day for moderate-to-high-intensity periods of training (1–3 h/day).67 It is important to note that these carbohydrate recommendations are largely extrapolated from endurance exercise studies. However, the same intake recommendations have also been advocated for stop-and-go sports such as tennis.66 ,68 ,70 ,71

The type of recovery food/snack consumed during short recovery periods should be easily digested carbohydrate sources.70 Players should avoid foods that are high in fat, protein and fibre to reduce the risk of gastrointestinal issues during a subsequent event.67 As there can be interindividual differences in gastrointestinal tolerance to certain foods and fluids, players should also take into consideration their individual preferences and previous experiences when selecting the timing, amount and source of carbohydrate to consume.

Protein

Another important nutritional aspect of recovery from tennis play is the ingestion of protein to promote resynthesis of muscle protein and aid in the muscle recovery process. Limited information is available on the postexercise protein needs of tennis players, thus recommendations are largely extrapolated from those targeted towards strength-trained and endurance athletes. The consumption of 20–25 g of protein after exercise is recommended in order to stimulate muscle protein synthesis and possibly lower the rate of muscle protein breakdown.72 Higher rates of protein intake after exercise have not been shown to confer additional benefits.72 The type and timing of protein ingestion are important considerations. A high-quality protein that provides all of the essential amino acids (leucine in particular) is needed for the adaptation to occur.72 The recommended timing for protein ingestion is as soon as possible after exercise, particularly if optimum muscle adaptation and performance are a high priority. To meet daily protein requirements (ie, in 24 h between sessions), it has been recommended that the tennis athlete training at a high intensity and duration on a daily basis consume ∼1.6 g protein/kg/day.66 This is similar to the 1.2–1.7 g protein/kg/day recommended for endurance and resistance-trained athletes.73

It is important to reiterate that tennis coaches and players should take into consideration the individual needs and preferences of the athlete. The nutrition recommendations outlined above are largely extrapolated from endurance-type activity conducted with college-aged individuals. Tennis competition is not only unique in its stop-and-go nature but also in its relatively brief opportunity for nutritional recovery between matches during tournament play. Rapid recovery is especially critical in this situation, thus more tennis-specific research is needed.