BRIEF REVIEW EFFECTS OF STRENGTH TRAINING ON RUNNING ECONOMY IN HIGHLY TRAINED RUNNERS:A SYSTEMATIC REVIEW WITH META-ANALYSIS OF CONTROLLED TRIALS CARLOS BALSALOBRE-FERNA ´ NDEZ, 1 JORDAN SANTOS-CONCEJERO, 2 AND GERASIMOS V. GRIVAS 3 1 Department of Physical Education, Sport and Human Movement, Autonomous University of Madrid, Madrid, Spain; 2 Department of Physical Education and Sport, University of the Basque Country UPV/EHU, Vitoria-Gasteiz, Spain; and 3 Department of Physical Education and Sport Science, University of Thessaly, Trikala, Greece ABSTRACT Balsalobre-Ferna ´ndez, C, Santos-Concejero, J, and Grivas, GV. Effects of strength training on running economy in highly trained runners: a systematic review with meta-analysis of con- trolled trials. J Strength Cond Res 30(8): 2361–2368, 2016— The purpose of this study was to perform a systematic review and meta-analysis of controlled trials to determine the effect of strength training programs on the running economy (RE) of high-level middle- and long-distance runners. Four electronic databases were searched in September 2015 (PubMed, SPORTDiscus, MEDLINE, and CINAHL) for original research articles. After analyzing 699 resultant original articles, studies were included if the following criteria were met: (a) participants were competitive middle- or long-distance runners; (b) partic- ipants had a V _ O 2 max .60 ml$kg 21 $min 21 ; (c) studies were controlled trials published in peer-reviewed journals; (d) stud- ies analyzed the effects of strength training programs with a duration greater than 4 weeks; and (e) RE was measured before and after the strength training intervention. Five studies met the inclusion criteria, resulting in a total sample size of 93 competitive, high-level middle- and long-distance runners. Four of the 5 included studies used low to moderate training inten- sities (40–70% one repetition maximum), and all of them used low to moderate training volume (2–4 resistance lower-body exercises plus up to 200 jumps and 5–10 short sprints) 2–3 times per week for 8–12 weeks. The meta-analyzed effect of strength training programs on RE in high-level middle- and long-distance runners showed a large, beneficial effect (stan- dardized mean difference [95% confidence interval] = 21.42 [22.23 to 20.60]). In conclusion, a strength training program including low to high intensity resistance exercises and plyo- metric exercises performed 2–3 times per week for 8–12 weeks is an appropriate strategy to improve RE in highly trained middle- and long-distance runners. KEY WORDS elite athletes, distance running, performance, resistance training, plyometrics INTRODUCTION S ustained running performance is reliant on a com- plex interaction of factors that lead to efficient mus- cular work and should result in a fast and effective running gait (25). Among the factors that may pre- dict middle- and long-distance running performance, running economy (RE), commonly defined as the steady-state V _ O 2 required at a given submaximal speed, has garnered the most attention over the last decade, although it is often still referred to as “being relatively ignored in the scientific literature” (12). Traditionally, biomechanical factors (30,50), muscle fiber distribution (7,38), age (28), sex, (8) and anthropometric fac- tors (32) have been found to account for interindividual var- iability in RE. However, RE is also largely influenced by training strategies, including a wide range of forms of strength training such as low-resistance training, high-resistance train- ing, explosive training, and plyometric training (3). These dif- ferent strength training modalities have been reported to improve RE not only in recreational runners but also in mod- erately trained and highly trained runners (3,4,58). Running economy improvements, a consequence of strength training interventions, have been attributed to improved lower- limb coordination and muscle coactivation, which would ultimately increase muscle stiffness and decrease ground contact times (37). Similarly, strength training interventions have been suggested to increase type I and type II fibers’ strength (53), resulting in less motor unit activation to produce a given force (3). This increase in strength may also improve biomechanical efficiency and muscle recruitment patterns (43), thus allowing a runner to run more efficiently at a given running speed. Address correspondence to Carlos Balsalobre-Ferna ´ndez, carlos. balsalobre@icloud.com. 30(8)/2361–2368 Journal of Strength and Conditioning Research Ó 2015 National Strength and Conditioning Association VOLUME 30 | NUMBER 8 | AUGUST 2016 | 2361 Copyright © National Strength and Conditioning Association Unauthorized reproduction of this article is prohibited.