4.2. Water Rescue
The average values of maximum heart rate reached during rescue (HR
Rescue) were around 93% of the maximum heart rate, similar to what happened in previous studies with lifeguards [
21], which shows a high energy expenditure and intense cardiovascular demand, as reported by Prieto et al. [
10].
From the heart rate reserve, which shows an almost exact relationship with the VO
2max [
22] it was observed that the average maximum effort during rescue was around 89% of the maximum oxygen uptake reached in the IPTL (VO
2IPTL). Although the intensity at which a rescue should be performed is not stipulated, some authors argue that it should be below 70% of the lifeguard’s maximum power capacity in order to avoid lactate accumulation [
15], thereby reaching a state of metabolic acidosis that could affect other out-of-water activities, such as performing CPR [
23]. However, other authors claim that a well-trained lifeguard should be able to perform quality CPR after a demanding rescue (L > 10 mmol·L
−1) [
19].
Independently of the intensity at which the rescue is performed, the application of basic life support in less than 10 min has been shown to be associated with better survival rates in a drowning victim [
24]. The less time spent on rescue, the greater the chances of survival [
3]. In previous studies, male rescuers completed 150 m rescues without flippers in approximately 260 s [
10,
25]. Salvador et al. [
8] observed that a group of young lifeguards completed a rescue twice the distance, 300 m, in just 288 s, in this case with flippers. In our case, also with flippers, the time for the 200 m rescue was 223 s (3 min and 43 s). This confirms the importance and effectiveness of flippers in the performance of a rescue in natural water spaces [
15,
26,
27].
The data recorded in this study show the possibility that lifeguards with a physical condition and technical mastery similar to those of the lifeguards of our study can perform a rescue of these characteristics in less than 4 min and, although the accumulated fatigue may cause problems when performing other subsequent tasks effectively, we consider that the lifeguard who intervenes in the rescue should do so at maximum intensity, in order to ensure the transfer of the victim to the mainland as soon as possible, and that the lifeguard who has not done the rescue should be the one who should start the cardiopulmonary resuscitation in an effective manner, if necessary [
25].
4.3. Relationship between IPTL and Water Rescue
The heart rate (HR) values showed differences between the values reached in the IPTL (HRIPTL) and those of the rescue (HRRescue) (
p < 0.001). It is possible that during the incremental test, the heart rate increases progressively from the beginning of the test until it ends, but in the water rescue the intensity is maximum as of the first moment. It has often been shown that in short, maximum tests, the slow component causes the heart rate and oxygen uptake values not to reach their maximum at the end of the test. However, it has been shown that with short and intense efforts, especially with duration greater than 3 min, it is possible to achieve maximum heart rate and VO
2max [
28]. Another reason why the maximum HR was not reached could be the intensity applied by the participants, although they were instructed to perform the rescue at maximum intensity from the beginning.
Blood lactate levels were significantly higher in the rescue than in the IPTL (
p < 0.001). It is possible that increased leg work during the transfer of the victim to the mainland is the reason for these differences [
16]. The HR and La values reached, as well as the rescue time (less than 4 min), indicate that anaerobic metabolism is also relevant in the energy contribution during rescue when performed at maximum intensity [
25].
The estimated oxygen uptake of the IPTL (VO2IPTL) showed significant correlations with rescue time (R
2 = 0.37;
p = 0.05), as Veronese da Costa and his collaborators [
29] showed with amateur swimmers in a 400 m freestyle event (R
2 = 0.55;
p < 0.05). These results are in line with the recommendations of the United States Lifesaving Association on the importance of developing aerobic power in lifeguards [
11].
Recently, Veronese da Costa and his collaborators [
20] confirmed with amateur swimmers the correlation between a 400 m freestyle test and the performance of an incremental pool test. In their study, the heart rate, as well as the maximum duration of the test, was measured before and after the test. The authors verified that the maximum time reached in the incremental test correlated significantly with the performance obtained in the 400 m test (R = −0.79;
p < 0.01). Due to this, they concluded that the performance of this test was related to middle-distance swimming tests, which could also be a tool to design more efficient training and, finally, to evaluate the physical condition of non-expert swimmers.
The results obtained in our study also revealed that the parameter showing the highest correlation with the effectiveness of water rescue is the maximum time reached in the IPTL (TimeIPTL y TimeRescue; R = −0.77; p < 0.001). Based on this correlation, a linear regression model was carried out confirming the relationship between the performance reached in the IPTL and the effectiveness in the rescue (R2 = 0.59; p < 0.001).
The similarities between the two tests (the swimming style and the material used) made it easier to estimate the effectiveness of the rescue. In the IPTL, as in the first part of the rescue, front crawl swimming was used, a style recommended in a water rescue [
30] and with which an energy expenditure similar to that obtained during the transfer of a victim is achieved [
31]. At the same time, both tests used flippers, one of the best-known and recommended materials for the performance of the lifeguard’s work [
26].