Sports Med https://doi.org/10.1007/s40279-018-0862-z REVIEW ARTICLE The Importance of Muscular Strength: Training Considerations 1 2 3 Timothy J. Suchomel • Sophia Nimphius • Christopher R. Bellon • Michael H. Stone4 Ó Springer International Publishing AG, part of Springer Nature 2018 Abstract This review covers underlying physiological exercises, plyometric exercise, unilateral exercise, and characteristics and training considerations that may affect kettlebell training may be limited in their potential to muscular strength including improving maximal force improve maximal strength but are still relevant to strength expression and time-limited force expression. Strength is development by challenging time-limited force expression underpinned by a combination of morphological and and differentially challenging motor demands. Training to neural factors including muscle cross-sectional area and failure may not be necessary to improve maximum architecture, musculotendinous stiffness, motor unit muscular strength and is likely not necessary for maxi- recruitment, rate coding, motor unit synchronization, and mum gains in strength. Indeed, programming that com- neuromuscular inhibition. Although single- and multi- bines heavy and light loads may improve strength and targeted block periodization models may produce the underpin other strength-power characteristics. Multiple greatest strength-power benefits, concepts within each sets appear to produce superior training benefits compared model must be considered within the limitations of the to single sets; however, an athlete’s training status and the sport, athletes, and schedules. Bilateral training, eccentric dose–response relationship must be considered. While 2- training and accentuated eccentric loading, and variable to 5-min interset rest intervals may produce the greatest resistance training may produce the greatest comprehen- strength-power benefits, rest interval length may vary sive strength adaptations. Bodyweight exercise, isolation based an athlete’s training age, fiber type, and genetics. Weaker athletes should focus on developing strength before emphasizing power-type training. Stronger athletes may begin to emphasize power-type training while maintaining/improving their strength. Future research should investigate how best to implement accentuated eccentric loading and variable resistance training and examine how initial strength affects an athlete’s ability to improve their performance following various training & Timothy J. Suchomel methods. [email protected] 1 Department of Human Movement Sciences, Carroll University, Waukesha, WI 53186, USA 2 Centre for Exercise and Sports Science Research, Edith Cowan University, Joondalup, Australia 3 Department of Exercise Science, LaGrange College, LaGrange, GA 30240, USA 4 Department of Exercise and Sport Sciences, Center of Excellence for Sport Science and Coach Education, East Tennessee State University, Johnson City, TN 37614, USA 123 T. J. Suchomel et al. 2 Literature Search Methodology Key Points Original and review journal articles were retrieved from Muscular strength development is underpinned by a electronic searches of PubMed and Medline (EBSCO) combination of morphological and neural factors databases. Additional searches of Google Scholar and rel- including muscle cross-sectional area and evant bibliographic hand searches with no limits of lan- architecture, musculotendinous stiffness, motor unit guage or year of publication were also completed. The recruitment, rate coding, motor unit synchronization, search strategy included the search terms ‘periodization’, and neuromuscular inhibition. ‘muscular strength’, ‘hypertrophy’, ‘cross-sectional area’, ‘bodyweight training’, ‘machine resistance training’, Bilateral training, eccentric and accentuated ‘weightlifting’, ‘weightlifting derivatives’, ‘plyometric eccentric training, and variable resistance appear to training’, ‘eccentric training’, ‘postactivation potentiation’, offer some advantages in producing the greatest ‘unilateral resistance training’, ‘variable resistance train- comprehensive strength adaptations. Bodyweight ing’, ‘kettlebell training’, ‘training to failure’, ‘training exercise, isolation exercises, plyometrics, unilateral status’, ‘rest interval’, ‘inter-repetition rest interval’, and exercise, and kettlebell training may be limited in ‘cluster sets’. The search concluded in July 2017. their potential to improve maximal strength but are Muscular strength may be expressed in several different still relevant to strength development by challenging forms including maximal dynamic strength, isometric time-limited force expression and differentially strength, and reactive strength [1]. This review primarily challenging motor demands. focuses on improving maximal dynamic strength. How- Weaker athletes should focus on developing a ever, it should be noted that by improving maximal foundation of strength before emphasizing power- dynamic strength, an athlete may also enhance maximal type training; however, stronger athletes may begin isometric strength [4, 5] and reactive strength characteris- to emphasize power-type training while maintaining tics [6–8]. A number of RT methods are discussed in this or improving their strength levels. article and those discussed were found to be the most prevalent within the existing literature. 3 Physiological Factors Affecting Muscular Strength 1 Introduction Muscular strength development is underpinned by a com- A recent review highlighted the importance of muscular bination of several morphological and neural factors. strength with regard to general and specific sport skills and However, the mechanisms that improve muscular strength their underpinning force characteristics, in addition to are considered multifactorial and can be influenced by reducing injury rates [1]. Given the relationship that other confounders such as initial strength [9], training strength (i.e., the ability to produce force against an status [10], and genetics [11]. The following provides a external resistance [2, 3]) has with a variety of attributes, brief overview of the morphological and neural factors that information regarding how to improve strength and the may combine to affect muscular strength. Understanding underpinning physiological factors that affect muscular these factors before discussing training considerations sets strength appears vital. If practitioners seek to improve their the context for the variety of responses in each of these athletes’ strength, they must first understand what physio- underpinning factors that culminate to elicit muscular logical changes have occurred or may occur in order to strength improvements. Although a thorough discussion is effectively prescribe resistance training (RT) progressions. beyond the scope of this review, it should be noted that an With a variety of training methods to choose from, it is athlete’s history of muscle contraction (e.g., fatigue, post- important that practitioners consider the literature that is activation, temperature, etc.) may influence the expression available in order to make informed programming deci- of muscular strength [12, 13]. sions to produce the best programs relative to the indi- vidual characteristics and needs of their athletes. The 3.1 Muscle Hypertrophy and Architecture purpose of this review is to identify underlying physio- logical factors and other training considerations (i.e., Evidence indicates that residual effects from previous methods, loading strategies, set configurations, and training training phases carry-over into future training phases status) that may affect muscular strength development. 123 The Importance of Muscular Strength: Training Considerations [14, 15]. Therefore, increasing hypertrophy in an effort to tension, etc.) may affect the hypertrophic response, a subsequently improve one’s strength has to do with thorough discussion of training methods is beyond the potentiation and residual training effects [16–18]. Thus, it scope of this review. For further information, readers are appears that there is a sequence or progression of training directed to a series of recent systematic reviews and meta- that, when followed, elicits the greatest benefits from RT. analyses that discuss best training practices for improving Specifically, evidence suggests that an order of first muscle hypertrophy [27–31]. increasing the muscle’s cross-sectional area (CSA) (i.e., hypertrophy) and work capacity (i.e., force production 3.2 Musculotendinous Stiffness capacity) [17–19], followed by a subsequent phasic pro- gression [20, 21], can produce superior strength-power Inherent to force production, and the subsequent force gains. Alterations in skeletal muscle hypertrophy can expression as a measure of strength, is the concept of our greatly impact a muscle’s ability to produce force and tissues expressing spring-like behavior which influences power. Simple observation offers some evidence as to the subsequent muscle performance [32]. Indeed, increased importance of larger CSAs in creating greater absolute tissue stiffness (i.e., the relationship between a given force force production; indeed, sports with body weight classes, and the amount of stretch the tissue undergoes [33]) can such as powerlifting and weightlifting, support this obser- enhance force transmission. Therefore, tendon stiffness vation. The rationale behind this is that a greater muscle adaptations [34], as well as the structures within the muscle fiber CSA, particularly type II fibers, may