Clasificación de los ataques inalámbricos.

2.8.1 Physiological effects of heat application

The application of superficial heat can have a number of physiological effects including increased subcutaneous and muscle temperatures (Myrer et al., 1994, Myrer et al., 1997), increased heart rate and cardiac output and decreased total peripheral resistance (Bonde- Petersen et al., 1992). These effects can subsequently increase short term blood flow (Song, 1984) due to peripheral vasodilation (Cochrane, 2004, Wilson et al., 2002). Following 5 min of heat application (hot-pack) to the calf, both muscle (0.74°C) and subcutaneous (8.13°C) temperatures increased substantially (Myrer et al., 1997). Similarly, muscle temperature increased substantially (2.83°C) throughout 20 min of immersion in hot water (40°C) (Myrer et al., 1994). Such increases can lead to increased skin and muscle blood flow (Figure 2.18) (Song, 1984) and are likely to occur due to an increase in vasodilation. Following a bout of either whole-body or local heating, cutaneous vascular conductance increased substantially in both groups (whole-body 380%, local 361%) with the increase determined to be evidence of a vasodilation response (Wilson et al., 2002). This response is thought to occur as a result of the increase in local temperature decreasing sympathetic nerve drive and increasing vessel diameter (Cochrane, 2004).

Figure 2.18: Change in leg skin and muscle blood flow resulting from exposure to different hot temperatures. Adapted from (Song, 1984).

Heart rate and cardiac output increased while total peripheral resistance decreased as a result of 15-20 min immersion in 43.8°C water (Figure 2.19) (Bonde-Petersen et al., 1992). The increase in blood flow is thought increase oxygen delivery which may assist in tissue repair and recovery (Cote et al., 1988, Wilcock et al., 2006a).

Figure 2.19: Change in heart rate (HR), cardiac output (CO) and total peripheral resistance per 100g of tissue (TRPPRU) resulting from passive rest (A) and hot water immersion (B). Adapted from (Bonde-Petersen et al., 1992). * P<0.05

Several contraindications exist with the use of hot water. High temperatures can lead to skin burns (Prentice, 1999) while compared to cold, heat can increase swelling and the

inflammatory response (Figure 2.20) (Cote et al., 1988). In turn, this may increase recovery time from damaging exercise. For AF players or other team sport athletes experiencing high physical contact or high eccentric loads causing damage, an increase in swelling and recovery time would not be desirable and may hamper match/training preparation.

Figure 2.20: Change in ankle volume (swelling) over 3 days of treatment after cold, heat and contrast bathing (Cote et al., 1988).

2.8.2 Physiological effects of contrast water therapy

During CWT, athletes alternate between hot and cold water immersion at regular intervals (i.e. 3:1 ratio of hot to cold) (Vaile et al., 2007). It is believed that CWT provides some of the benefits of both cold and hot immersion, including temperature changes which promote vasodilation and vasoconstriction, leading to a ‘vaso-pumping’ action and an increase in blood flow. It is theorised that this pumping action improves venous return and can potentially reduce the oedema/swelling associated with injury (Fiscus et al., 2005, Prentice, 1999, Starkey, 1999). The effect of CWT on blood flow has been examined (Fiscus et al., 2005). Following a 20 min CWT protocol (4 min at 40o_{C alternating with 1 min at 13}o_{C) lower leg blood flow showed} substantial fluctuations compared to a control group. The increases were attributed to a substantial increase in blood flow over baseline by the hot phase of the protocol, while the cold application reduced blood flow (Figure 2.21). Although the 4:1 ratio indicated substantial blood flow changes resulting from water temperature changes, a ratio of 1:1 or 2:1 hot/cold is much

more common than the 4:1 ratio used by the authors, particularly in a team sport setting (Dawson et al., 1997, Higgins et al., 2011, King and Duffield, 2009, Kinugasa and Kilding, 2009).

Figure 2.21: Change in arterial blood flow during contrast water immersion (Fiscus et al., 2005). Note that baseline indicates the point when blood flow measurements began.

In order for vaso-pumping to occur, muscle temperature and not just skin temperature needs to change (Wilcock et al., 2006a). The effects of CWT on increasing/decreasing muscle temperature has been investigated (Myrer et al., 1994). Muscle temperature following either 20 min of CWT (4 x 4 min hot at 40.6°C followed by 1 min cold at 15.6°C) or hot water immersion (20 min at 40.6°C) was measured. Results indicate that hot water immersion substantially increased baseline muscle temperature, however, during CWT, muscle temperature failed to increase (Figure 2.22) (Myrer et al., 1994). The effects of heat application may be counteracted by the application of cold (i.e. lowering muscle temperature) therefore muscle temperature during CWT may remain unchanged.

Figure 2.22: Change in muscle temperature resulting from contrast water immersion. Adapted from (Myrer et al., 1994).

As the exposure to hot temperatures during typical team sport application is limited to a 1:1 or 2:1 ratio it is possible that the substantial increases in blood flow demonstrated by Fiscus et al., 2005 will not be seen. Vaso-pumping occurs at slow rates (Wilcock et al., 2006a), and as team sport participants typically alter between hot and cold water 2-6 times, pumping may occur only 2-6 times over the total duration of a recovery intervention (Dawson et al., 1997, Higgins et al., 2011, King and Duffield, 2009, Kinugasa and Kilding, 2009). Muscle temperatures do not change greatly during CWT and if athletes spend limited time in hot water, it seems probable that vaso-pumping would play only a minor role in reducing exercise/contact induced oedema and assisting recovery.

The effects of hydrostatic pressure however may help to explain why CWT may be effective in oedema reduction. Following an eccentric leg press protocol, effectiveness of 15 min CWT (1 min at 8-10°C alternating with 2 min at 40-42°C) on reducing thigh volume over 72 h (Vaile et al., 2007) was compared to a passive recovery. Contrast water therapy produced smaller increases and faster reductions in thigh circumference compared to the passive treatment after 24 (CWT 3.2%, PAS 6.2%), 48 (3.1%, PAS 6.6%) and 72 h (1.0%, PAS 3.9%). As subjects were exposed to short periods of hot water during the 2:1 hot/cold recovery protocol, it is likely

that hydrostatic pressure played a larger role in reducing oedema than vaso-pumping. Similarly, following an eccentric leg press protocol, 14 min of CWT (1 min at 15° C alternating with 1 min at 38° C) ameliorated increases in thigh circumference/swelling after 24 (CWT 0.35%, PAS 1.4%), 48 (CWT 0.2%, PAS 1.4%) and 72 h (CWT 0.2%, PAS 1.1%) (Vaile et al., 2008c).

Contrast water therapy is a commonly used modality in athletic settings and even though it can help to reduce swelling and oedema, athletes will be primarily concerned with the ability of the modality to restore physical function. This will be discussed below.