Strength Training in Swimming

his narrative review deals with the topic of strength training in swimming, which has been a controversial issue for decades. It is not only about the importance for the performance at start, turn and swim speed, but also about the question of how to design a strength training program. Different approaches are discussed in the literature, with two aspects in the foreground. On the one hand is the discussion about the optimal intensity in strength training and, on the other hand, is the question of how speci c strength training should be designed. In addition to a summary of the current state of research regarding the importance of strength training for swimming, the article shows which physiological adaptations should be achieved in order to be able to increase performance in the long term. Furthermore, an attempt is made to explain why some training contents seem to be rather unsuitable when it comes to increasing strength as a basis for higher performance in the start, turn and clean swimming. Practical

training for swimming, the article shows which physiological adaptations should be achieved in order to be able to increase performance in the long term. Furthermore, an attempt is made to explain why some training contents seem to be rather unsuitable when it comes to increasing strength as a basis for higher performance in the start, turn and clean swimming. Practical training consequences are then derived from this. Regardless of the athlete's performance development, preventive aspects should also be considered in the discussion. The article provides a critical overview of the abovementioned key issues. The most important points when designing a strength training program for swimming are a suf ciently high-load intensity to increase maximum strength, which in turn is the basis for power, year-round strength training, parallel to swim training and working on the transfer of acquired strength skills in swim training, and not through supposedly speci c strength training exercises on land or in the water. Keywords: resistance training; start performance; turn performance; preventive training; elite swimmers 1. Introduction The importance of strength or strength training for swimming performance has been discussed since the early 20th century. It is particularly associated with Robert Kiphuth, who was likely one of the rst swimming coaches in the 1920s–1930s to implement training outside the pool (dry-land training) in the attempt to strengthen the muscles relevant to swimming performance [1,2]. The importance of strength training for swimming has been and still is the subject of debate, and its ability to impact swimming performance is often underestimated by some authors [3]. However, in addition to the performance gains associated with strength training, it is important to consider the injury preventive aspects of integrating strength training into the swimmers' preparations [4]. Obviously, keeping the swimmer healthy is the primary aim but is also a fundamental prerequisite for the realization of the training plan and, based on this, a high level of performance. However, based on the available literature on strength training and swimming, there are contradictory approaches and several arguments for different strength training meth- ods, and their meanings are only partially empirically justi ed.

healthy is the primary aim but is also a fundamental prerequisite for the realization of the training plan and, based on this, a high level of performance. However, based on the available literature on strength training and swimming, there are contradictory approaches and several arguments for different strength training meth- ods, and their meanings are only partially empirically justi ed. For example, Morouço Int. J. Environ. Res. Public Health2022,19, 5369.

Int. J. Environ. Res. Public Health2022,19, 5369 2 of 32 and colleagues [5] write that it is unclear from a scienti c perspective whether strength training helps to increase swimming performance and how such training would have to be designed to optimize performance. Questions about the correct periodization of strength training over the course of the season or the annual training plan are also often completely disregarded. Consequently, there are no concrete recommendations for how strength training should be integrated into the individual season contained within the annual training plan for swimmers. A particular problem for the planning of training in swimming is the development of performance-relevant strength (e.g., maximum strength, rate of force development) in combination with predominantly endurance-oriented water- based training activities because extensive endurance training can negatively in uence optimal strength development [6]. Although simultaneous strength and endurance training provide competing stimuli that trigger differing adaptive mechanisms [7–11], studies on other endurance sports, such as triathlon [12] and cross-country skiing [13], have reported that strength training can be used successfully despite high volumes in endurance training. This problem also applies to the large training volumes that are commonly undertaken in competitive or high-performance swimming. However, a pure volume orientation in endurance training is no longer considered contemporary [14–17], which also applies specif- ically to swimming [18–29]. Several research groups emphasize and/or provide evidence that supports the importance of anaerobic energy supply for competitive swim distances up to 200 m [18,30–34]. The exclusive focus on training volume, which is reportedly up to 110 km per week [35], still prevails in some national swim programs. However, such an approach must be questioned, as it does not consider the metabolic requirements of the different competition distances. Costill and co-workers [24] (p. 376) write on this problem: “Since the majority of the competitive swimming events last less than 3 min, it is dif cult to understand how training at speeds that are markedly slower than competitive pace for 3–4 h d 1 will prepare the swimmer for the supramaximal efforts of competition”. The success of an accompanying strength training program is

(p. 376) write on this problem: “Since the majority of the competitive swimming events last less than 3 min, it is dif cult to understand how training at speeds that are markedly slower than competitive pace for 3–4 h d 1 will prepare the swimmer for the supramaximal efforts of competition”. The success of an accompanying strength training program is likely to depend primar- ily on the optimal combination of the different strength training and endurance training strategies integrated into the swimmers training program, whereby it is not possible to avoid interactions due to the large number of performance factors to be triggered. In the following article, we rstly provide an evidenced-based overview on the importance of strength training for swimming. This is followed by the basic requirements for the design of strength training so that it can produce the desired adaptations. 2. Aims of Strength Training in Swimming The primary objectives of integrating strength training into the preparation practices of swimmers is to prevent the degenerative changes in the active and passive musculoskeletal system and the improvements in various strength parameters (e.g., maximum strength, rate of force development) that in uence competition performance. In addition to the in uence of strength training on the generation of impulses in the swimming movement, improvements in performance at the start and during the turns are of particular importance for competition success. 2.1. Preventive Aspects of Strength Training for Swimmers The need for early and regular strength training arises from the observation of overuse injuries typical of swimming. The regions of the body affected are primarily the spine[ , shoulders [35–41,43,45,47–53] and knees [36–38,40,41,43,54–56]. The causes of these issues are, in particular, orthopedically unfavorable movement sequences (e.g., the leg kick in breaststroke with the consequences of overtraining the medial collateral ligament and/or chondromalacia of the patella, medial compartment synovitis, inflammation and fibrosis of the synovial plica; shoulder: subacromial or intra-articular impingement, reduced gleno- humeral stability; spine: degenerative disk changes), incorrect techniques (e.g., stretched arm guidance in the recovery phase in crawl and dolphin swimming, increased lordosis

the consequences of overtraining the medial collateral ligament and/or chondromalacia of the patella, medial compartment synovitis, inflammation and fibrosis of the synovial plica; shoulder: subacromial or intra-articular impingement, reduced gleno- humeral stability; spine: degenerative disk changes), incorrect techniques (e.g., stretched arm guidance in the recovery phase in crawl and dolphin swimming, increased lordosis

Int. J. Environ. Res. Public Health2022,19, 5369 3 of 32 during dolphin swimming) and incorrect use of training aids [4]. Various authors link the use of paddles to the occurrence of shoulder injuries [41,49,52]. The following circumstances are associated with these occurrences [35,44,49–51,57,58]: a high volume of training in the water; early entry into the sport; strength training on land with incorrect technique; a rapid increase in swim training volume; a dependence on the styles swum (primarily breaststroke and dolphin); exercises in the water that lead to increased lordosis of the spine while using assistive devices. While several researchers have reported that the bone structure of competitive swim- mers does not differ from that of untrained individuals [59–67], others report signi cantly impaired bone structure (e.g., bone mineral content, bone mineral density) [68–71]. Various studies have reported that adolescent and adult swimmers have a lower bone mineral den- sity than athletes from weight-bearing and strength-based sports [59,60,64,72–77]. These impairments primarily affect the lumbar region of the spine and the lower extremity. Degen- erative changes in the spine have been documented by several research groups [57,78–80]. For example, Kaneoka and colleagues [81] have reported that about two-thirds of all swim- mers studied demonstrate degenerative changes to the spine, which is often associated with self-reported back pain. One factor, which may be associated with reductions in bone density issues, is likely related to the high proportion of weight-relieving training in the water [78]. In this context, the positive in uence of strength training on bone structure should be noted [62,64,65,75,82–93]. Accordingly, resilience can be increased by in uenc- ing the bone structure at an early stage through regular strength training. Apart from classical strength training, any form of “high impact” loading, such as plyometrics, is recommended [61–63,67,75,91,92,94–98]. Both the load intensity and the load volume are of great importance for the development of the bone structure [59–61,99–104]. In addition to the positive effect on bone mineralization, strength training can also improve the stability of knee, hip and shoulder joints. Better joint control could lead to a reduction in joint irritation. However, it

as plyometrics, is recommended [61–63,67,75,91,92,94–98]. Both the load intensity and the load volume are of great importance for the development of the bone structure [59–61,99–104]. In addition to the positive effect on bone mineralization, strength training can also improve the stability of knee, hip and shoulder joints. Better joint control could lead to a reduction in joint irritation. However, it is important to note that strength training must be carefully planned and integrated into the training process. If strength training is simply added to the existing training volume, this would lead to an increase in the total training load and consequently increase the risk of overtraining. As such, strength training should not be started if the swimmer displays any sign of overreaching or overtraining. If strength training is incorporated into the swimmer's training plan, it is important that the remaining swim training volume must be adapted (signi cantly reduced) to account for the new training content. It is important to note that, from a preventive point of view, strength training should be started early in the athlete's long-term development plan as starting strength training before puberty can ensure the athlete establish good bone structures [62,82,98,105–107]. In the case of shoulder problems, training must be critically analyzed, especially where work is carried out against increased resistance from joint angles that are dif cult to stabilize, which is often the case with so-called “speci c” strength training exercises on cable traction devices (e.g., biokinetic swim bench). 2.2. Strength Training to Increase the Strength Abilities of the Muscles Used to Propel the Swimmer In addition to injury prevention effects of strength training, it is also important to consider the performance bene ts of this type of training. Special attention should be paid to both swim starts and turns, as well as the swimming movement itself as this can also bene t from strength training. By increasing the total impulse, resulting from increasing the partial impulses of the arms and legs, the propulsion speed can be increased. 2.2.1. Increase in the Impulse of Swimming Movements What Should Be Called Strength Training? From a biomechanical

both swim starts and turns, as well as the swimming movement itself as this can also bene t from strength training. By increasing the total impulse, resulting from increasing the partial impulses of the arms and legs, the propulsion speed can be increased. 2.2.1. Increase in the Impulse of Swimming Movements What Should Be Called Strength Training? From a biomechanical point of view, an increase in swimming speed can be achieved in two ways. Firstly, this can be achieved by optimizing the cycle frequency and/or lengthening the swim stroke. There is, however, a distance-dependent, optimal relationship

Int. J. Environ. Res. Public Health2022,19, 5369 4 of 32 between cycle path and frequency, as an increase in frequency can lead to a reduction in cycle path and vice versa. Lengthening of the cycle path can be achieved in two ways: rstly, by reducing the braking force (negative acceleration: e.g., inhibiting water resistance) and secondly, by increasing the propulsive forces. Strength training can positively in uence both the cycle frequency and the cycle path (by increasing the propulsive force) [108,109]. The extent of the effect of strength training depends on the level of performance and the competition distance. To increase the overall propulsive force is the result of increasing the force of a single movement, which can be achieved by developing maximum strength. In addition, in the case of repetitive cyclic loading over time, the reduction in impulses must be kept as low as possible. This is mainly carried out by training the competition-speci c metabolic situation. The term “strength endurance” is often used in this context [110]. Strength endurance refers to the ability of the neuromuscular system to realize the highest possible sum of impulses during a given time period against higher resistances. Impulse: P Total= n å i=1 t i2Z t i1 F i(t)dt (1) Impulse consists of the magnitude of the single force impact and the ability to keep the reduction of these force impacts as low as possible (fatigue resistance). It should be noted that the exact border at which strength endurance is distinguished from endurance perfor- mance is not clearly de ned in the literature. This often leads to supposedly contradictory statements regarding the role of strength endurance in swimming. The term strength training should only be used when central nervous adaptations, associated with a high degree of activation (nearly complete activation of the motoneuron pool in a short time frame) and/or morphological adaptations are the long term training goal. Such adaptations are typically linked to the use of high intensity training loads (relative to maximum strength (1 RM)). For the untrained, relatively low load intensities, which should not fall below 50 to 60%

a high degree of activation (nearly complete activation of the motoneuron pool in a short time frame) and/or morphological adaptations are the long term training goal. Such adaptations are typically linked to the use of high intensity training loads (relative to maximum strength (1 RM)). For the untrained, relatively low load intensities, which should not fall below 50 to 60% of the 1 RM, these are initially suf cient. However, no positive adaptations (e.g., for improving bone structure) are to be expected at low load intensities, even for the untrained [91]. Due to the high energy demand and the fact that at intensities above 50–60% of maximum strength, blood ow to the muscle is severely impaired [111,112], the energetic demands are primarily supplied by anaerobic metabolism [85,113]. The further the training load deviates from an intensive activation of the musculature by the central nervous system and a dominant anaerobic energy supply to a more frequent and lower training load, the lower the contribution of strength training to performance. After a maximum of two to three minutes, it can be assumed that aerobic energy supply dominates [114–117]. A distinction between strength and endurance training is physiologically dif cult to justify and is therefore always arbitrary. However, it makes sense to assign training loads with force inputs of less than 50–60% of the maximum force and thus dominantly aerobic metabolic state to endurance training, as they do not lead to neuronal and morphological adaptations that are characteristic of strength training in the long term [118,119]. However, it is important to note that at the beginning of strength training, even lower intensities can be effective for a few months [120,121]. Training with lower intensities tends to lead to long-term metabolic adaptations, which are probably better developed with swim-speci c training in the water. When considering training intensity, it can be assumed that in the long term, use of intensities below 80% of the 1 RM does not further enhance the active (muscle) and passive (e.g., bone) musculoskeletal system, which are often considered to be primary goals of strength training [122]. This also explains

probably better developed with swim-speci c training in the water. When considering training intensity, it can be assumed that in the long term, use of intensities below 80% of the 1 RM does not further enhance the active (muscle) and passive (e.g., bone) musculoskeletal system, which are often considered to be primary goals of strength training [122]. This also explains why training with high numbers of repetitions and low intensities does not further enhance strength gains after a few weeks and months of training and therefore should be considered as ineffective for enhancing high level performances. Based on this line of reasoning, strength endurance training is not advisable for swimmers, even when incorporated as a method of training variation. For athletes with low strength levels, a positive effect of training with low loads on the stroke frequency (i.e., an increase in the number of power

The article provides a critical overview of strength training's importance for swimming performance.