a b s t r a c t

Purpose: The aim of this study was to analyze the effects of a recovery program based on foam roller with and without vibration on blood Lactate clearance and perceived fatigue after a water rescue.

Methods: A quasi-experimental Crossover design was carried out to compare passive (PR) recovery and a short protocol of foam roller (FR) and vibration foam roller (VFR) recovery after a 100 m water rescue in 7 volunteer lifeguards. Blood lactate and perceived exertion were measured before and after the rescue, and also after the 5-min recovery intervention.

Results: Blood lactate levels decrease significantly with foam roller (p = 0.013; effect size = 0.97) and vibration foam roller recovery (p < 0.001; effect size = 1.62). passive recovery did not show significant differences clearing out blood lactate. Fatigue perceived decrease significantly with all the recovery methods, but foam roller has higher effects on the global fatigue and VFR on the legs.

Conclusion: FR and VFR clear out more blood lactate and decrease fatigue more than PR, with the subsequently increase of the physical conditioning to perform another effort.

(C) 2021 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://

creativecommons.org/licenses/by-nc-nd/4.0/).

1. Introduction

Drowning is a global health problem, causing around 295,210 deaths every year and being one of the leading causes of death among Young people [1]. The drowning process occurs rapidly and it has demon- strated than more than 5 min of submersion decrease the chances of survival [2-4]. Drowning situations at the beach, usually occur between 50 and 100 m from the shore [5]. Prevention is the best strategy to avoid drowning, but when this tasks fail lifeguards have to start the rescue im- mediately and perform it as fast as possible to increase the possibilities of survival [2]. In this sense, interrupt the drowning process is one of the main favorable outcomes factors [4] therefore a fast water rescue has a very high importance [6], but also the physical condition, as a water res- cue requires high levels of intensity [7]. All of this involves an exhausting process with high physiological demands and results in a great elevation of blood lactate concentrations, around 10 mmol.l-1 [8,9]. Moreover, sometimes lifeguards have to solve multiple situations in a day, with more than one water rescue, but maintaining their ability and success [5,10]. Therefore, the effectively recovery between events is considered an important determinant in lifesaving [11,12]. At this re- spect, previous studies have investigated the effectiveness of different

* Corresponding author at: Facultade de Ciencias da Educacion e do Deporte, Campus A Xunqueira, 36005 Pontevedra, Spain.

E-mail address: [email protected] (M. Lorenzo-Martinez).

recovery methods to improve lifeguards performance, such as electrostimulation [11] or foam roller (FR) [12], showing positive effects in recovery with interventions around 20 min, in comparison with the passive recovery (PR). However, these situations are time-dependent and do not allow long Recovery times. Multiple incidents in the aquatic environment occur in a very Short period of time, for example with the entry of series of waves or the appearance strong wind or rip currents [10].

Previous studies investigated how lifeguards could benefit from shorter interventions targeted to the areas involved in the water rescue (i.e. the lower limb) [11,12] or even from new recovery tools such as vibration foam roller (VFR) which has been demonstrated to increase recovery in other populations [13,14]. Therefore, this study aimed to analyze the effectiveness of three recovery modalities: FR, VFR and PR, after a water rescue on blood lactate clearance and perceived exhaustion.

1. Method

A quasi-experimental crossover design was conducted in order to assess the effectiveness of three recovery modalities: PR, FR and VFR on blood lactate clearance and perceived exhaustion in lifeguards after a water rescue (Fig. 1).

https://doi.org/10.1016/j.ajem.2021.04.089

0735-6757/(C) 2021 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Fig. 1. Flow chart outlining the design and intervention.

• 1. Sample

10 lifeguards were voluntarily recruited for this study and after methodological problems 7 subjects completed the 3 recovery modali- ties (28.6% women, age 23.29 +- 1.11 years, height 173.43 +- 8.6 cm, weight 76.57 +- 5.94 kg). All participants carried out the 3 recovery methods after performing a water rescue, in three different days. This investigation was approved by the Ethics Committee of the Faculty of Education and Sport Sciences (08-0721) and developed according to the Declaration of Helsinki. Prior to the study, subjects were informed about all the procedures and signed a written informed consent.

• 1. Water rescue

The water rescue was performed by lifeguards with fins and wetsuits in the estuary of Pontevedra, Galicia, Spain (Latitude: 42.4222432, Longitude: 8.6821066) during November and December 2020 and under similar conditions with calm sea and waves <0.5 m (Douglas scale value 0-2), wind speed <5 m/s, water temperature be- tween 13 ?C and 14 ?C and ambiental temperature between 17.5 ?C and 20.5 ?C. The weather was reported by the local forecast agency (Meteogalicia). The rescue was carried out with a test-approved water rescue manikin [15] and it consisted of swimming 100 m with fins to- wards the manikin, controlling it, towing the manikin 100 m back to the shore and then extract the manikin to the dry sand, [8,11,12].

• 1. Recovery

In this research, 3 recovery modalities were tested to study their in- fluence in blood lactate and perceived exhaustion. FR and VFR have been suggested as appropriate recovery tools after water rescues, and PR was chosen as a control situation. All subjects were instructed in foam rolling with and without vibration before the test. After the water rescue, participants were asked to take off their wetsuits and

start the recovery protocol. The 3 situations were performed by each participant in randomized order, with a total intervention time of 5 min.

• • 1. Passive recovery

During PR, participants remained rested and seated during the whole duration of the recovery period, simulating an immediate return to the watchtower.

• • 1. Foam roller and vibration foam roller recovery

The FR and VFR interventions consisted of rolling with the device on quadriceps and hamstrings of both legs, since they are the main muscle involved in swimming with fins [16]. Participants were trained in foam rolling with and without vibration before the intervention. Each muscle was rolled in two sets: 30 s of rolling, 15 s of rest and 30 s of rolling again for each muscle [17]. The final time of the recovery protocol was 5 min. For both interventions, a high density foam roller was used (Vyper, Hyperice, Irvine, CA, USA) and in the VFR intervention the foam roller was set at 18 Hz, which is within the optimal frequency range to influ- ence musculoskeletal system [18]. Participants were instructed to stay first in a prone position and locate the device on the upper area of the quadriceps, and then compress the muscle while moving across the muscle belly. For hamstrings, subjects locate the foam roller under the ischial tuberosity and compress, moving across the muscle belly. In both interventions, to standardize the amount of pressure exerted on each muscle, a numerical rating scale was used (0 = no discomfort, 10 = maximal discomfort) and participants were asked to perform the interventions with a value of 6 to 7 on this scale [19].

• 1. Variables

The time of the water rescue was recorded in seconds. Blood lactate measurements were taken in 6 different moments: basal conditions (LB), after water rescue (L1), after recovery protocol (L2), 3 min post re- covery (L3), 6 min post recovery (L4) and 9 min post recovery (L5). All measurements were assessed with a capillary device (LactateScout.

SensLab GmbH, Leipzig, Germany) and expressed in mmol/l, with and accuracy of +-3% (minimal standard deviation: +-0.2 mmol/l). The per- ceived fatigue was measured through the Rated Perceived Exertion scale (RPE) after the water rescue and after recovery in five areas: global, arms, chest and legs.

• 1. Statistical analysis

All analyses were conducted using the statistical package SPSS for Macintosh (version 25.0. Armonk, NY: IBM Corp). The normality of dis- tribution for each variable was checked both graphically and using the Shapiro-Wilk test. The descriptive results of these variables are pre- sented by mean +- standard deviation (SD). A repeated-measures anal- ysis of variance (ANOVA) was used to analyze the rescue time of participants according to each type of recovery. The differences in blood lactate measurements and variables of RPE scale were analyzed using a repeated-measures ANOVA with two intra-subject factors (recovery and moment). Partial eta-squared (?²) effect sizes were also calculated for this analysis. A value ?² >= 0.01 indicates a small effect,

p

p

>=0.059 a medium, and >= 0.138 a large effect [20]. Pair-wise comparisons between lactate and RPE measurements were conducted via Bonferroni post-hoc test, using Cohens’ d to calculate effect sizes. These effects were classified as trivial (d < 0.2) small (0.2 < d < 0.5), medium (0.5 < d < 0.8), and large (d >= 0.8) [20]. For all analysis, the significance value was set at p <= 0.05.

1. Results

In this study, 21 water rescues were completed and then 3 different types of recovery were carried out: PR, FR and VFR. Subjects performed the intervention in three different days, one for each recovery modality, with similar conditions. In this regard, there were no significant differ- ences among the different recovery modalities neither in rescue time (PR: 225.43 +- 18.06 s, FR: 229 +- 15.44 s, VFR: 224.71 +- 23.13 s; p >

0.05) nor in baseline blood lactate (PR: 1.83 +- 0.62 mmol.l^-1, FR: 1.74 +- 0.72 mmol.l^-1, VFR: 1.51 +- 0.44 mmol.l^-1; p > 0.05).

Regarding the comparison of blood lactate with the different types of recovery (Table 1), the results of repeated-measures ANOVA showed significant differences according to the moment (p < 0.001; ?² = 0.95, large) but no significant differences according to the recovery (p = 0.97; ?² = 0.005, trivial) or the interaction between moment and recovery (p = 0.707; ?² = 0.11, small). The PR did not show any significant differences in blood lactate levels in the different moments (p > 0.05). However, blood lactate levels decrease significantly with FR (L5 vs L2; p = 0.013; d = 0.97, large) and with VFR (L5 vs L1; p = 0.037; d = 1.24, large / L5 vs L2; p = 0.001; d = 1.62, large / L4 vs L2; p = 0.044; d = 1.24, large).

p

p

p

The fatigue of the participants was measured with the RPE scale after the water rescue and after recovery in 4 different areas: global, arms, chest and legs (Fig. 2). Significant differences were found regarding the moment in global (p < 0.001; ?² = 0.92, large), arms (p = 0.009;

p

?² = 0.70, medium), chest (p = 0.001; ?² = 0.88, large) and legs

found regarding the type of recovery or the interaction between mo- ment and recovery in any area (p > 0.05).

In the pair-wise comparisons, global fatigue decrease significantly post recovery in comparison with post rescue in PR (p < 0.001; d = 2.71, large), FR (p < 0.001, d = 3.01, large) and VFR recovery (p < 0.001, d = 2.16, large). In the arms, fatigue decrease significantly after recovery in comparison with after rescue in PR (p < 0.006; d = 1.62, large), FR (p < 0.047, d = 0.97, large) and VFR recovery (p < 0.028, d = 1.42). In the chest, comparisons showed a significant decrease of chest fatigue with PR (p = 0.001; d = 2.54, large), FR (p < 0.001, d = 1.79) and VFR recovery (p < 0.001, d = 1.68, large). Finally, on the legs a significant decrease of fatigue was described with PR (p < 0.001; d = 1.67, large), FR (p = 0.001, d = 1.75, large) and VFR recovery (p = 0.001, d = 2.74).

1. Discussion

The present study analysed three different recovery modalities per- formed after a water rescue on Physiological parameters such as blood lactate clearance and perceived exertion. Considering that prior re- search with similar purposes and recovery methods completed inter- ventions of about 20 min [11,12], to the best of authors’ knowledge this is the first study assessing a short-time protocol based on active re- covery with foam rolling. Furthermore, the use of vibration in foam rolling is an emerging technique which has been recently tested in other variables or populations [21-23], but to our knowledge this is the first time that foam rolling with vibration is used as a recovery mo- dality in lifeguards after a water rescue.

The main results showed that in 5 min of recovery, lifeguards appear to clear out more lactate with both FR and VFR than with PR. In addition, FR only decreased blood lactate significantly 9 min after recovery in comparison with the post recovery measurement, but VFR obtained a significant clearance of blood lactate 6 and 9 min after recovery in com- parison with post recovery and 9 min after recovery in comparison with post rescue, with higher effects than FR. Thus, FR and VFR could repre- sent valuable aids in the recovery after rescue and improve lifesavers readiness to next rescues. These findings are consistent with previous research and confirm that active recovery forms remove blood lactate more quickly than passive recovery, as it has been demonstrated in pre- vious research with lifeguards [11,12] and other populations [9,24]. Al- though underlying mechanisms supporting the increase in blood lactate removal as a consequence of FR remain unclear, it could be related with their effects on cardiovascular system such as reduction of arterial stiff- ness, increase of blood flow, and improvement of vascular endothelial function [25-27].

In the same vein, active recovery using FR has been recently con- firmed as an adequate recovery tool after great efforts with high muscle fatigue [28,29], such as water rescues, and adding vibration appears to increase its benefits in pain perception after muscle fatigue [13]. Even though there is still a lack of knowledge about physiological recovery re- lated to VFR, it is suggested as a fast and effective method for fatigue

management and could allow rescuers to be in better conditions after

p p

(p < 0.001, ?² = 0.94, large). However, no significant differences were

p

Table 1

Comparison between blood lactate measurements (mean +- SD).

L1	L2	L3	L4	L5
PR 10.24 +- 1.76	10.09 +- 0.94	9.06 +- 0.95	8.04 +- 1.64	7.61 +- 1.93
FR 10.34 +- 2.37	10.47 +- 3.19	9.41 +- 2.24	8.59 +- 2.65	7.63 +- 2.61#
VFR 10.10 +- 2.50	11.31 +- 2.84	9.57 +- 3.07	8.23 +- 2.05#	7.09 +- 2.36?#

PR: passive recovery; FR: foam roller recovery; VFR: vibration foam roller recovery; L1: lactate after water rescue; L2: lactate after recovery; L3: lactate 3 min post recovery; L4: lactate 6 min post recovery; L5: lactate 9 min post recovery.

* Significant difference (p < 0.05) with L1.

^# Significant difference (p < 0.05) with L2.

a water rescue and perform a consequent rescue with as quality and safety as possible.

Conversely, results of the RPE showed that all the variables decrease significantly after recovery in comparison with post rescue in all areas but FR appears to have more effects than other recovery modalities in the global fatigue, probably due to the effects of FR increasing blood flow parameters and muscle oxygen saturation, which have been dem- onstrated to influence the perceived exertion [13,25]. In addition, VFR appears to have a higher effect decreasing the perceived fatigue of the legs in comparison with other recovery methods, suggesting that apart from the effects on blood flow, the vibration could produce a local neurophysiological effect and through the Golgi tendon organs in- duce tissue relaxation in the central nervous system [22]. During water rescues the whole body is involved, but specifically when the rescuer is

Fig. 2. Results of RPE scale.

swimming back to the shore with the victim, the lower limb performs all the effort to tow the victim. Therefore, the decrease of perceived fa- tigue on the legs with a short protocol of VFR could be a helpful strategy to maintain the ability of the lifeguards when performing more than one water rescue or managing a multiple victim situation, using only 5 min to reach a significant decrease in their fatigue.

• 1. Practical applications

In a lifesaving, a fast and safety rescue is a goal for lifeguards, in spe- cial if the prior rescuers conditions are under muscular acidosis. The re- sults of this study present VFR as a new active recovery modality after a water rescue that achieves in 5 min a decrease of 30% in blood lactate and a significant decrease of the perceived fatigue on the legs, so life- guards and other rescuers may benefit from these short-time interven- tions in situations with multiple victims or adverse environmental conditions. Foam rolling is not excessively expensive, as foam rollers can be found from $20 without vibration to $200 with vibration. In com- parison with other common rescue equipment and the relationship be- tween the cost-benefit to the safety does not seem unaffordable for lifeguard teams.

• 1. Limitations

Several limitations should be considered in this study. First, the sam- ple size with 7 lifeguards and 21 water rescues completed made results should be read carefully and future investigations with bigger sample sizes may confirm these findings. The VFR was tested at only one fre- quency (18 Hz), but other frequencies may have produce different results.

1. Conclusion

In conclusion, FR clear out more blood lactate than PR and VFR clear out more blood lactate than PR and FR, and besides decrease the per- ceived fatigue on the lower limb, with the subsequently increase of the physical conditioning to perform another effort.

Funding source

Funding for open access charges: Universidade de Vigo / CISUG

Authors contribution statement

All authors contributed substantially to the development of the work. Alejandra Alonso-Calvete and Anton Lage-Rey participated in the conception and design of the study. Miguel Lorenzo-Martinez and Ezequiel Rey contributed to the methodology and statistical analysis of the data. All authors contributed to the writing of the manuscript and reviewed the final version which is submitted to the journal.

Declaration of Competing Interest

None.

Acknowledgments

Authors want to thank the team of lifeguards involved in this study for their participation and Dr. Roberto Barcala-Furelos for his collaboration.

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