Fundamentals or Icing on Top of the Cake? A Narrative Review of Recovery Strategies and Devices for Athletes

he sport and athletic performance industry has seen a plethora of new recovery devices and technologies over recent years, and it has become somewhat dif cult for athletes, coaches, and practitioners to navigate the ef cacy of such devices or whether they are even required at all. With the increase in recovery devices and tools, it has also become commonplace for athletes to overlook more traditional, well-established recovery strategies. In this narrative review, we discuss recovery strategies in relation to the hierarchy of scienti c evidence, classifying them based on the strength of the evidence, ranging from meta-analyses through to case studies and reports. We report that foam rolling, compression garments, cryotherapy, photobiomodulation, hydrotherapy, and active recovery have a high level of positive evidence for improved recovery outcomes, while sauna, recovery boots/sleeves, occlusion cuffs, and massage guns currently have a lower level of evidence and mixed results for their ef cacy. Finally, we provide guidance for practitioners when deciding on recovery strategies to use with athletes during different phases of the season. Keywords:compression; ice baths; cold water immersion; sport performance; massage guns 1. Introduction The selection of recovery devices and technologies available for use by athletes has experienced substantial growth in recent years as athletes seek effective, time-ef cient, and often portable methods to improve physical recovery after training

on recovery strategies to use with athletes during different phases of the season. Keywords:compression; ice baths; cold water immersion; sport performance; massage guns 1. Introduction The selection of recovery devices and technologies available for use by athletes has experienced substantial growth in recent years as athletes seek effective, time-ef cient, and often portable methods to improve physical recovery after training and competition. New devices and strategies become rapidly popular and publicised on social media, while “recovery centres” charge a premium for access to a variety of devices, aimed at both athletes and the public alike. With this increased focus on “recovery” and these various devices and tools, it has become somewhat dif cult for athletes, coaches, and practitioners to navigate the ef cacy of such devices and determine if there is any risk of harm. It has also become commonplace for athletes to overlook more traditional, well-established recovery strategies like sleep and appropriate nutrition practices, contributing to a mismatch between what coaches rate as effective recovery strategies and what athletes rate as being the most effective [1]. Among the various assertions made by manufacturers of recovery devices, the primary objective is typically to alleviate muscle soreness, mitigate overall feelings of fatigue, and enhance an athlete's capacity to tolerate their training workload. Some strategies or devices may concomitantly target other aspects of recovery that may aid physiological (e.g., increased blood ow and reduced metabolic waste), biomechanical (e.g., increased range of motion), neurological (e.g., reduced central nervous system fatigue), or psychological (e.g., increased mood, motivation, and readiness to train) factors, but essentially, a key component of most of these devices is to reduce the perception of soreness and increase feelings of recovery. At present, it is dif cult to establish the validity of these claims, as the popularity of such devices precedes clear evidence from experimental research. This narrative review will discuss the purpose of recovery strategies and the funda- mentals of recovery (sleep, nutrition, and training periodisation), before categorising other Sports2023,11, 213.

of these claims, as the popularity of such devices precedes clear evidence from experimental research. This narrative review will discuss the purpose of recovery strategies and the funda- mentals of recovery (sleep, nutrition, and training periodisation), before categorising other Sports2023,11, 213.

Sports2023,11, 213 2 of 15 recovery strategies by their current level of evidence. Additionally, this review will discuss the chronic use of recovery strategies and future considerations in this eld of research. 2. The Purpose of Recovery Put simply, training is the application of acute physical challenges to the body over time in order to maximise physiological capability [2]. Recovery, therefore, is the time outside of training where these improvements in physiological capability will actually transpire, and must be carefully balanced with training stress to optimise performance while avoiding maladaptation, injury, or illness [3]. Recovery modalities are implemented to act across various physiological, biomechanical, neurological, or psychological domains [4] (summarised in Table), though athletes primarily report reducing muscle soreness as the main purpose of implementing recovery strategies [1,5]. Muscle soreness results from mechanical disruption and in ammation of the muscle bres, which causes the release of enzymes that sensitize the nerves within the muscle, producing pain when the muscle contracts or is stretched [6]. The in ammation and microtrauma that occur in the muscle cell are essential for the muscle tissue to strengthen and adapt, allowing them to produce force again without the same degree of damage occurring (the “repeated-bout effect”) [7]. While muscle soreness is unlikely to signi cantly impact athletic performance, excessive levels of muscle soreness may discourage athletes from engaging in further exercise or lead them to reduce intensity in subsequent training sessions [8]. Although, it should be noted that muscle soreness and delayed-onset muscle soreness (DOMS) in particular are usually associated with intense, unfamiliar, or eccentric-based exercise [8], rather than regular training. As such, it may be problematic to extrapolate the ndings of recovery research conducted on lesser-trained participants to elite or highly-trained athletes who complete regular, familiar training [7]. Table 1.Proposed effects of recovery modalities on various domains perturbed during exercise and examples of recovery modalities that purport to act upon these domains.Example Recovery Modalities Physiological Improved blood ow Reduced heart rate Increased heart rate variability Decreased blood pressure Reduced skin and core body temperatures Hormonal changes (e.g., reduced cortisol and increased growth hormone) Reduced

regular, familiar training [7]. Table 1.Proposed effects of recovery modalities on various domains perturbed during exercise and examples of recovery modalities that purport to act upon these domains.Example Recovery Modalities Physiological Improved blood ow Reduced heart rate Increased heart rate variability Decreased blood pressure Reduced skin and core body temperatures Hormonal changes (e.g., reduced cortisol and increased growth hormone) Reduced oedema Improved removal of metabolic by-products Active recovery; compression garments; cryotherapy chambers; electromyostimulation; hydrotherapy; occlusion cuffs; photobiomodulation; sauna Biomechanical Improved muscle–tendon compliance Improved limb/joint range of motion Restoration of isometric strength and peak torque Decreased active and passive stiffness Decreased tissue adhesion Compression garments; foam rolling; stretching; massage guns; recovery boots/sleeves Neurological Reduced muscle tension and spasm Reduction in neuromuscular excitability Reduced pain response Compression garments; cryotherapy chambers; electromyostimulation; oat tanks; foam rolling; massage guns Psychological Improved mood state Reduced anxiety Reduction in feelings of fatigue Increased feelings of relaxation Decreased perceived muscle soreness Compression garments; oat tanks; hydrotherapy; occlusion cuffs; photobiomodulation; recovery boots/sleeves; sauna

Sports2023,11, 213 3 of 15 Regular training is a necessary part of being an athlete, and without any recovery interventions, individuals will naturally recover at their own rate following exercise. How- ever, the underlying theory behind utilising recovery interventions is that they have the potential to expedite this process [7]. Incorporating different recovery strategies might permit athletes to minimise the deleterious effects of muscle soreness and perceived fatigue, ultimately allowing for maintenance of subsequent training and competition performance. If a particular strategy alleviates muscle soreness, for example, this may in turn allow an athlete to train sooner, with greater quality and/or with a higher volume/intensity. This is based on the theory of supercompensation, whereby acute central and peripheral fatigue induced by an exercise bout can be restored by a period of recovery, allowing for physiological adaptations to take place and ultimately restoring or improving physiological capacity and athletic performance [3]. 3. The Fundamentals of Recovery Athletes' perceptions of recovery methods often do not align with current scienti c evi- dence [5], and as such, athletes may overlook some of the more well-established methods of recovery in favour of new or novel recovery technologies. While research evidence is weak or sparse on many of these newer technologies like massage guns, occlusion cuffs, and recovery boots/sleeves, there is a greater level of empirical support for the fundamental recovery strategies of sleep, nutrition, and periodisation and their role in athletic recov- ery. These fundamentals (“the cake”; Figure) have a much greater overall contribution to athletic recovery and performance than any potential marginal improvements from added devices/tools (“the icing”) and must therefore be monitored and optimised before considering the implementation of further strategies or devices.Sports 2023, 11, x FOR PEER REVIEW 4 of 16 Figure 1. The fundamentals and examples of some “icing on top of the cake” strategies for recovery in athletes. 3.1. Sleep Sleep is an essential process for the optimal maintenance of an athlete’s health and plays a critical role in the psychophysiological recovery of an athlete when many restora- tive bodily functions and processes take place. It is well recognised

Figure 1. The fundamentals and examples of some “icing on top of the cake” strategies for recovery in athletes. 3.1. Sleep Sleep is an essential process for the optimal maintenance of an athlete’s health and plays a critical role in the psychophysiological recovery of an athlete when many restora- tive bodily functions and processes take place. It is well recognised that sleep loss impairs numerous functions, including cognition, memory consolidation, immunity, and, im- portantly, athletic performance [9]. Despite this, elite athletes in the professional era are facing more intensive physical training loads, competition loads, and high levels of mental stress on a regular basis, resulting in several factors that could have an influence on sleep disturbances. Alongside this, various studies have identified that athletes may struggle to obtain the recommended 7–9 hours of sleep per night due to different sport- (e.g., early morning training) and non-sport-related factors (e.g., study commitments), therefore compromising their recovery [9]. Yet, increasing nightly sleep duration can improve sprint time, reaction time, aerobic capacity, and body composition [10,11]. The importance that sleep has on the health, recovery, and performance of athletes is clearly highlighted by the rapid increase in research regarding sleep in athletic popula- tions, with over 80% of the overall journal articles published in this field in the last decade [12]. Technological advancements in sleep measuring and monitoring have also advanced this field of research as wearable technologies approach the accuracy of research-grade actigraphy for detecting sleep and wake [13]. However, caution should be taken when using data from these wearables for other purposes, such as informing training, accurately identifying sleep phases, or diagnosing sleep disorders [14]. Simple sleep diaries or ath- lete-specific sleep questionnaires [15,16] can provide insight into areas for improvement, while sleep hygiene education may yield short-term improvements in sleep quality and duration in athletes [17–19]. SLEEP NUTRITION PERIODISATION EMS Float Tanks Massage Guns Compression Garments Foam Rolling Occlusion Cuffs Cryotherapy Chambers Hydrotherapy Photobiomodulation Therapy Active Recovery Stretching Saunas Massage Inflatable Sleeves Figure 1. The fundamentals and examples of some “icing on top of the cake” strategies for recovery in athletes.

sleep hygiene education may yield short-term improvements in sleep quality and duration in athletes [17–19]. SLEEP NUTRITION PERIODISATION EMS Float Tanks Massage Guns Compression Garments Foam Rolling Occlusion Cuffs Cryotherapy Chambers Hydrotherapy Photobiomodulation Therapy Active Recovery Stretching Saunas Massage Inflatable Sleeves Figure 1. The fundamentals and examples of some “icing on top of the cake” strategies for recovery in athletes.

Sports2023,11, 213 4 of 15 3.1. Sleep Sleep is an essential process for the optimal maintenance of an athlete's health and plays a critical role in the psychophysiological recovery of an athlete when many restorative bodily functions and processes take place. It is well recognised that sleep loss impairs nu- merous functions, including cognition, memory consolidation, immunity, and, importantly, athletic performance [9]. Despite this, elite athletes in the professional era are facing more intensive physical training loads, competition loads, and high levels of mental stress on a regular basis, resulting in several factors that could have an in uence on sleep disturbances. Alongside this, various studies have identi ed that athletes may struggle to obtain the recommended 7–9 h of sleep per night due to different sport- (e.g., early morning training) and non-sport-related factors (e.g., study commitments), therefore compromising their recovery [9]. Yet, increasing nightly sleep duration can improve sprint time, reaction time, aerobic capacity, and body composition [10,11]. The importance that sleep has on the health, recovery, and performance of athletes is clearly highlighted by the rapid increase in research regarding sleep in athletic populations, with over 80% of the overall journal articles published in this eld in the last decade [12]. Technological advancements in sleep measuring and monitoring have also advanced this eld of research as wearable technologies approach the accuracy of research-grade actigraphy for detecting sleep and wake [13]. However, caution should be taken when using data from these wearables for other purposes, such as informing training, accurately identifying sleep phases, or diagnosing sleep disorders [14]. Simple sleep diaries or athlete- speci c sleep questionnaires [15,16] can provide insight into areas for improvement, while sleep hygiene education may yield short-term improvements in sleep quality and duration in athletes [17–19]. 3.2. Nutrition Maintaining adequate dietary energy intake is paramount for athletes to promote energy availability for training and reduce the risk of injury and illness. Strategies for recov- ery nutrition will be sport- and sex-dependent [20], but the fundamentals are considered to be the following: (i) refuelling (replacing carbohydrates after exercise), (ii) rebuilding (intake of protein to aid

athletes [17–19]. 3.2. Nutrition Maintaining adequate dietary energy intake is paramount for athletes to promote energy availability for training and reduce the risk of injury and illness. Strategies for recov- ery nutrition will be sport- and sex-dependent [20], but the fundamentals are considered to be the following: (i) refuelling (replacing carbohydrates after exercise), (ii) rebuilding (intake of protein to aid in muscle repair and growth), and (iii) rehydrating (maintaining uid intake, especially in the summer months) [21]. Meeting these primary needs and ensuring adequate nutritional intake (macro- and micro-nutrients) to meet overall energy requirements should be rst and foremost in nutrition planning [22]. The use of certain nutritional supplements may also be encouraged to support training and competition de- mands, with guidance from previous reviews that have categorised the available evidence on these supplements [23–25]. 3.3. Periodisation Structured physical training is based upon the principles of progressive overload and adaptation, whereby an increasing training stimulus is applied over time to elicit phys- iological adaptations and improvements in performance [3]. Training load—comprised of training volume, intensity, and frequency—must be manipulated appropriately over microcycles (weeks), mesocycles (months), and macrocycles (seasons) to maintain or im- prove physiological capabilities [26]. Planning recovery within and across these cycles is necessary and should consider the characteristics of individual training sessions (e.g., metabolic demand), individual variations in the recovery process, and desired physical adaptations [26]. Time away from the sport/training environment, rest, social recovery, and downtime are all important factors that need to be considered in the overall periodised plan. Insuf cient recovery will not only impact an athlete's performance in subsequent training bouts but will also curtail the potential physiological adaptations from the initial training bout and thereby fail to meet the basic purpose of the training process [3]. The type and duration of recovery periods can be manipulated across a competitive season depending on the desired outcome; for example, withholding or limiting structured

Sports2023,11, 213 5 of 15 recovery interventions during a pre-season phase to promote physical adaptations to maximal training stress [27]. However, continuing to overload training volume (or any aspect thereof) while limiting recovery can place athletes at risk of non-functional over- reaching or overtraining [28]. The latter represents a chronic imbalance between training and recovery, manifesting primarily as a prolonged performance decrement, though other symptoms can be apparent [28]. This underlies the importance of athlete monitoring (including both objective and subjective measures) to capture an individual's response to training load over time and inform acute adjustments to training as required [29]. 4. Categorising Recovery Strategies To evaluate the ef cacy and usefulness of various recovery strategies, the hierarchy of scienti c evidence can be applied (Figure). This system of grading scienti c evidence recognises that different study designs in uence the reliability and validity of study results; however, it may overlook the overall feasibility of an intervention [30]. This is relevant when considering that some of the new or emerging recovery tools have only been evaluated in case studies or small-sized experimental trials (if at all), and therefore a meta-analysis or systematic review is not warranted. As such, this hierarchy for evaluating the quality of evidence can be seen as a guideline and a suitable starting point for assessing different recovery devices and strategies. The next section will discuss this hierarchy of evidence in two parts (as indicated by 1 and 2 in Figure recovery strategies/devices that fall under these categories. We acknowledge that there are other recovery strategies and devices that are used by athletes that are not covered in this review, and it is beyond the scope of this paper to discuss all recovery modalities; however, based on previous literature [1,31–33], we have selected some of the most popular strategies implemented by athletes.Sports 2023, 11, x FOR PEER REVIEW 6 of 16 modalities; however, based on previous literature [1,31–33], we have selected some of the most popular strategies implemented by athletes. Figure 2. Hierarchy of scientific evidence to consider when evaluating different strategies and their efficacy. 4.1. High-Level

previous literature [1,31–33], we have selected some of the most popular strategies implemented by athletes.Sports 2023, 11, x FOR PEER REVIEW 6 of 16 modalities; however, based on previous literature [1,31–33], we have selected some of the most popular strategies implemented by athletes. Figure 2. Hierarchy of scientific evidence to consider when evaluating different strategies and their efficacy. 4.1. High-Level of Evidence The most rigorous level of evidence for a particular topic is often established through meta-analyses and systematic reviews, which summarise individual studies and the qual- ity of these studies according to specific criteria. The following recovery strategies, which have been the subject of meta-analyses and/or systematic reviews, will be discussed in this section: foam rolling, compression garments, EMS, cryotherapy chambers, photobiomod- ulation, hydrotherapy, active recovery, and stretching. It is important to note that while certain strategies may have a high level of evidence (e.g., via meta-analyses and systematic reviews), that does not mean that the evidence is positive for that particular strategy. 4.1.1. Foam Rolling Foam rolling is a form of self-massage that is purported to enable myofascial release and improve flexibility and range of motion [34], and it has been the subject of a number of meta-analyses and reviews. Overall, it appears that foam rolling is an effective method of improving range of motion (ROM) following exercise [34], with the optimal “dose” being 90–120 seconds of rolling per muscle group [35]. As well, foam rolling appears to reduce DOMS and increase pressure-to-pain thresholds after exercise and therefore may optimise recovery from training [35]. While the ROM and DOMS benefits seem relatively consistent across studies and there appears to be no detrimental effect on recovery, the actual performance recovery benefits are less clear. Very few studies have shown that in- creased ROM or decreased DOMS translates to athletic performance (e.g., isokinetic strength, jumping, or agility) following foam rolling as a recovery strategy [36,37]. Figure 2. Hierarchy of scienti c evidence to consider when evaluating different strategies and their ef cacy. 4.1. High-Level of Evidence The most rigorous level of evidence for a particular topic is often established through

This review discusses recovery strategies and devices for athletes, evaluating their efficacy and evidence levels.