Strength

Muscle strength refers to the ability to produce force against an external resistance.[reference|url=https://pubmed.ncbi.nlm.nih.gov/29372481|title=The Importance of Muscular Strength: Training Considerations.|published=2018-Apr|authors=Suchomel TJ, Nimphius S, Bellon CR, Stone MH|journal=Sports Med|] It is often divided into specific types of strength, such as lower body strength or upper body strength.

Strength is commonly assessed using dynamic resistance exercise,[reference|url=https://pubmed.ncbi.nlm.nih.gov/26838985|title=The Importance of Muscular Strength in Athletic Performance|published=2016 Oct|authors=Suchomel TJ, Nimphius S, Stone MH|journal=Sports Med|] which includes concentric (muscle shortening) and eccentric (muscle lengthening) muscle actions. The most popular method is a 1-repetition maximum (1RM) test,[reference|url=https://pubmed.ncbi.nlm.nih.gov/24497158|title=A brief review of strength and ballistic assessment methodologies in sport.|published=2014-May|authors=McMaster DT, Gill N, Cronin J, McGuigan M|journal=Sports Med|] which involves lifting as much weight as possible for one repetition using either free weights or an exercise machine. A higher-repetition maximum test (i.e., a 2–6 RM) may also be used to assess strength and estimate 1RM strength.[reference|url=https://pubmed.ncbi.nlm.nih.gov/26838985|title=The Importance of Muscular Strength in Athletic Performance|published=2016 Oct|authors=Suchomel TJ, Nimphius S, Stone MH|journal=Sports Med|]

Another option is an isometric strength test, which involves producing a maximal force against an immovable resistance.[reference|url=https://pubmed.ncbi.nlm.nih.gov/8819238|title=The use of isometric tests of muscular function in athletic assessment.|published=1996-Jul|authors=Wilson GJ, Murphy AJ|journal=Sports Med|] Unlike dynamic resistance exercise, the muscle length does not change during an isometric muscle action. Strong correlations have been reported between maximum dynamic and isometric strength.[reference|url=https://pubmed.ncbi.nlm.nih.gov/24497158|title=A brief review of strength and ballistic assessment methodologies in sport.|published=2014-May|authors=McMaster DT, Gill N, Cronin J, McGuigan M|journal=Sports Med|]

In accordance with the principle of specificity — which states that training adaptations are specific to the demands imposed on the body — heavy loads (≥ 80% of 1RM) are superior to lighter loads for increasing 1RM strength.[reference|url=https://pubmed.ncbi.nlm.nih.gov/35015560|title=Muscle hypertrophy and strength gains after resistance training with different volume-matched loads: a systematic review and meta-analysis.|published=2022-Apr|authors=Carvalho L, Junior RM, Barreira J, Schoenfeld BJ, Orazem J, Barroso R|journal=Appl Physiol Nutr Metab|][reference|url=https://pubmed.ncbi.nlm.nih.gov/33433148|title=Resistance Training Load Effects on Muscle Hypertrophy and Strength Gain: Systematic Review and Network Meta-analysis|published=2020 Dec 26|authors=Pedro Lopez, Regis Radaelli, Dennis R Taaffe, Robert U Newton, Daniel A Galvão, Gabriel S Trajano, Juliana Teodoro, William J Kraemer, Keijo Häkkinen, Ronei S Pinto|journal=Med Sci Sports Exerc|] Training to muscular failure (i.e., the point at which another concentric repetition cannot be completed with proper form) is not necessary to increase muscle strength.[reference|url=https://pubmed.ncbi.nlm.nih.gov/33497853|title=Effects of resistance training performed to repetition failure or non-failure on muscular strength and hypertrophy: A systematic review and meta-analysis.|published=2022-03|authors=Grgic J, Schoenfeld BJ, Orazem J, Sabol F|journal=J Sport Health Sci|] In fact, ending each set a few reps shy of failure appears to be superior to training to failure for maximizing gains in 1RM strength.[reference|url=https://pubmed.ncbi.nlm.nih.gov/35038063|title=The Effect of Load and Volume Autoregulation on Muscular Strength and Hypertrophy: A Systematic Review and Meta-Analysis.|published=2022-Jan-15|authors=Hickmott LM, Chilibeck PD, Shaw KA, Butcher SJ|journal=Sports Med Open|][reference|url=https://osf.io/preprints/sportrxiv/v3tr9/||title=The effects of different intra-set velocity loss thresholds on lower-limb adaptations to resistance training in young adults: A systematic review and meta-analysis|authors=Gantois et al|published=2021-06] Also, rest intervals between sets should be at least 3 minutes.[reference|url=https://pubmed.ncbi.nlm.nih.gov/36157335|title=Manipulating Resistance Training Variables to Induce Muscle Strength and Hypertrophy: A Brief Narrative Review.|published=2022|authors=DE Camargo JBB, Brigatto FA, Zaroni RS, Trindade TB, Germano MD, Junior ACT, DE Oliveira TP, Marchetti PH, Prestes J, Lopes CR|journal=Int J Exerc Sci|][reference|url=https://pubmed.ncbi.nlm.nih.gov/19204579|title=American College of Sports Medicine position stand. Progression models in resistance training for healthy adults|published=2009 Mar|authors=American College of Sports Medicine|journal=Med Sci Sports Exerc|]

Supplements marketed to enhance muscle strength typically claim to do so through one of the following mechanisms or a combination of them: increasing muscle contractile efficiency (e.g., by improving calcium handling in the sarcoplasmic reticulum), delaying muscular fatigue, increasing the availability of fuel sources (e.g., carbohydrate), and/or stimulating muscle protein synthesis.[reference|url=https://journals.lww.com/nsca-scj/Abstract/2020/10000/Emerging_Nutritional_Supplements_for_Strength_and.7.aspx|title=Emerging Nutritional Supplements for Strength and Hypertrophy: An Update of the Current Literature|authors=Gonzalez et al\journal=Strength and Conditioning Journal|published=2020-10]

The most effective supplements for increasing muscle strength appear to be creatine,[reference|url=https://pubmed.ncbi.nlm.nih.gov/34199588|title=Creatine for Exercise and Sports Performance, with Recovery Considerations for Healthy Populations.|published=2021-Jun-02|authors=Wax B, Kerksick CM, Jagim AR, Mayo JJ, Lyons BC, Kreider RB|journal=Nutrients|] protein,[reference|url=https://pubmed.ncbi.nlm.nih.gov/28698222|title=A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults|published=2018 Mar|authors=Morton RW, Murphy KT, McKellar SR, Schoenfeld BJ, Henselmans M, Helms E, Aragon AA, Devries MC, Banfield L, Krieger JW, Phillips SM|journal=Br J Sports Med|] and caffeine.[reference|url=https://pubmed.ncbi.nlm.nih.gov/34291426|title=Effects of Caffeine on Resistance Exercise: A Review of Recent Research.|published=2021-11|authors=Grgic J|journal=Sports Med|] Other supplements that have been studied for muscle strength include nitrate, citrulline malate, HMB, alpha-GPC, taurine, ashwagandha, and omega-3 fatty acids.

Nutrition plays an important role in increasing muscle strength through fueling exercise and promoting recovery and exercise-induced adaptations. These processes are mainly influenced by protein and carbohydrate intake. Evidence suggests that a total daily protein intake of about 1.6 grams per kilogram of body weight is ideal for supporting increases in strength.[reference|url=https://pubmed.ncbi.nlm.nih.gov/21660839|title=Nutrition guidelines for strength sports: sprinting, weightlifting, throwing events, and bodybuilding.|published=2011|authors=Slater G, Phillips SM|journal=J Sports Sci|][reference|url=https://pubmed.ncbi.nlm.nih.gov/28698222|title=A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults|published=2018 Mar|authors=Morton RW, Murphy KT, McKellar SR, Schoenfeld BJ, Henselmans M, Helms E, Aragon AA, Devries MC, Banfield L, Krieger JW, Phillips SM|journal=Br J Sports Med|]

Muscle glycogen is a primary fuel source during resistance exercise,[reference|url=https://pubmed.ncbi.nlm.nih.gov/12076177|title=Fatigue during high-intensity intermittent exercise: application to bodybuilding.|published=2002|authors=Lambert CP, Flynn MG|journal=Sports Med|] and glycogen depletion is associated with muscle fatigue and impaired muscle contraction efficiency,[reference|url=https://pubmed.ncbi.nlm.nih.gov/33900579|title=Muscle Glycogen Metabolism and High-Intensity Exercise Performance: A Narrative Review|published=2021 Sep|authors=Jeppe F Vigh-Larsen, Niels Ørtenblad, Lawrence L Spriet, Kristian Overgaard, Magni Mohr|journal=Sports Med|] so consuming at least 3–5 grams of carbohydrate per kilogram of body weight per day is recommended to maximize strength gains.[reference|url=https://pubmed.ncbi.nlm.nih.gov/21660839|title=Nutrition guidelines for strength sports: sprinting, weightlifting, throwing events, and bodybuilding.|published=2011|authors=Slater G, Phillips SM|journal=J Sports Sci|]

With that said, many studies have not found differences in strength gains between higher- and lower-carbohydrate diets,[reference|url=https://pubmed.ncbi.nlm.nih.gov/35215506|title=The Effect of Carbohydrate Intake on Strength and Resistance Training Performance: A Systematic Review.|published=2022-Feb-18|authors=Henselmans M, Bjørnsen T, Hedderman R, Vårvik FT|journal=Nutrients|] particularly when the resistance exercise routine includes low volumes (< 10 sets per workout), high loads (≥ 80% of 1-repetition maximum), and long rest periods (≥ 3 minutes of rest between sets). However, there is a lack of evidence demonstrating benefits of lower-carbohydrate diets for muscle strength.

Differences in muscle strength between individuals seem to be mostly explained by differences in muscle mass,[reference|url=https://pubmed.ncbi.nlm.nih.gov/34617822|title=Behavior of motor units during submaximal isometric contractions in chronically strength-trained individuals.|published=2021-Nov-01|authors=Casolo A, Del Vecchio A, Balshaw TG, Maeo S, Lanza MB, Felici F, Folland JP, Farina D|journal=J Appl Physiol (1985)|][reference|url=https://pubmed.ncbi.nlm.nih.gov/32187154|title=Performance and Anthropometrics of Classic Powerlifters: Which Characteristics Matter?|published=2022-Apr-01|authors=Ferrari L, Colosio AL, Teso M, Pogliaghi S|journal=J Strength Cond Res|][reference|url=https://pubmed.ncbi.nlm.nih.gov/11990746|title=The role of FFM accumulation and skeletal muscle architecture in powerlifting performance.|published=2002-Feb|authors=Brechue WF, Abe T|journal=Eur J Appl Physiol|][reference|url=https://pubmed.ncbi.nlm.nih.gov/19153760|title=Anatomical predictors of maximum isometric and concentric knee extensor moment.|published=2009-Apr|authors=Blazevich AJ, Coleman DR, Horne S, Cannavan D|journal=Eur J Appl Physiol|][reference|url=https://sciendo.com/article/10.2478/v10078-010-0040-3|title=Correlations of Anthropometric and Body Composition Variables with the Performance of Young Elite Weightlifters|authors=Siahkouhian and Hedayatneja|journal=Journal of Human Kinetics|published=2009-01] which is supported by the mechanistic rationale that a larger muscle has greater force-generating capacity.[reference|url=https://pubmed.ncbi.nlm.nih.gov/31016546|title=Exercise-Induced Myofibrillar Hypertrophy is a Contributory Cause of Gains in Muscle Strength|published=2019 Jul|authors=Taber CB, Vigotsky A, Nuckols G, Haun CT|journal=Sports Med|] Other contributors to muscle strength include neural factors,[reference|url=https://pubmed.ncbi.nlm.nih.gov/29372481|title=The Importance of Muscular Strength: Training Considerations.|published=2018-Apr|authors=Suchomel TJ, Nimphius S, Bellon CR, Stone MH|journal=Sports Med|] such as the threshold at which motor units are recruited and the motor unit discharge rate, and genetics.[reference|url=https://pubmed.ncbi.nlm.nih.gov/34366884|title=Effects of Genetic Variation on Endurance Performance, Muscle Strength, and Injury Susceptibility in Sports: A Systematic Review.|published=2021|authors=Appel M, Zentgraf K, Krüger K, Alack K|journal=Front Physiol|] Additionally, simply practicing the test used to examine strength (e.g., a back squat 1-repetition maximum) can promote increases in strength.[reference|url=https://pubmed.ncbi.nlm.nih.gov/28463902|title=Practicing the Test Produces Strength Equivalent to Higher Volume Training.|published=2017-Sep|authors=Mattocks KT, Buckner SL, Jessee MB, Dankel SJ, Mouser JG, Loenneke JP|journal=Med Sci Sports Exerc|][reference|url=https://pubmed.ncbi.nlm.nih.gov/27875635|title=Muscle adaptations following 21 consecutive days of strength test familiarization compared with traditional training.|published=2017-Aug|authors=Dankel SJ, Counts BR, Barnett BE, Buckner SL, Abe T, Loenneke JP|journal=Muscle Nerve|]