Background: Although lower-body strength is correlated with sprint performance, whether increases in lower-body strength transfer positively to sprint performance remain unclear.
Objectives: This meta-analysis determined whether increases in lower-body strength (measured with the free-weight back squat exercise) transfer positively to sprint performance, and identified the effects of various subject characteristics and resistance-training variables on the magnitude of sprint improvement.
Methods: A computerized search was conducted in ADONIS, ERIC, SPORTDiscus, EBSCOhost, Google Scholar, MEDLINE and PubMed databases, and references of original studies and reviews were searched for further relevant studies. The analysis comprised 510 subjects and 85 effect sizes (ESs), nested with 26 experimental and 11 control groups and 15 studies.
Results: There is a transfer between increases in lower-body strength and sprint performance as indicated by a very large significant correlation (r = −0.77; p = 0.0001) between squat strength ES and sprint ES. Additionally, the magnitude of sprint improvement is affected by the level of practice (p = 0.03) and body mass (r = 0.35; p = 0.011) of the subject, the frequency of resistance-training sessions per week (r = 0.50; p = 0.001) and the rest interval between sets of resistance-training exercises (r = −0.47; p ≤ 0.001). Conversely, the magnitude of sprint improvement is not affected by the athlete’s age (p = 0.86) and height (p = 0.08), the resistance-training methods used through the training intervention, (p = 0.06), average load intensity [% of 1 repetition maximum (RM)] used during the resistance-training sessions (p = 0.34), training program duration (p = 0.16), number of exercises per session (p = 0.16), number of sets per exercise (p = 0.06) and number of repetitions per set (p = 0.48).
Conclusions: Increases in lower-body strength transfer positively to sprint performance. The magnitude of sprint improvement is affected by numerous subject characteristics and resistance-training variables, but the large difference in number of ESs available should be taken into consideration. Overall, the reported improvement in sprint performance (sprint ES = −0.87, mean sprint improvement = 3.11 %) resulting from resistance training is of practical relevance for coaches and athletes in sport activities requiring high levels of speed.
Alex’s Notes: Okay, I fully admit this study is more of a common sense confirmation. Using our critical thinking skills, it is easy to think that having greater lower body strength would translate to greater speed and velocity during sprints assuming all else constant because more strength means greater peak force and rate of force production with every stride. Outside of critical thinking, broscience confirms this idea with, “dude have you seen elite sprinters? Especially compared to their marathon counterparts, they are feaking ripped.” No doubt, sprinters have significant muscle mass, and science has come to the rescue again by showing significant correlations between back squat 1RM and sprint performance.
While it is clear that strength is important for sprinters, it is unclear whether resistance-training, per se, improves sprint performance. Moreover, even if the connection was clear, various resistance-training variables such as the duration, volume, intensity, and methodology of training, can influence the transferability of training-induced strength gains to the sprint. Thus,
“The purpose of this systematic review with meta-analysis was to (1) determine whether increases in lower-body strength positively transfer to sprint performance and (2) establish the relative importance of various subject characteristics and resistance-training variables on sprint improvement.”
The review only included randomized controlled trials that used a free-weight back squat (full, parallel, or half) as the strength measurement. Overall, 15 studies were included that underwent effect size (ES) analysis, which for this meta-analysis was the difference between the post- and pre-sprint tests. Not surprisingly, squat strength was significantly correlated with reduced sprint time, while body mass was moderately correlated with increased sprint time (reduced speed). Additionally, the frequency of resistance training sessions performed per week and the average inter-set rest interval length moderately reduced and increased sprint performance, respectively. No correlations between sprint performance and age, height, or training methodology were present.
So it is confirmed that strength benefits sprint performance. But more importantly, the meta-analysis found that resistance training independent of squat strength, improved sprint times by 4% for elite athletes, suggesting it may be a worthwhile investment where everything can ride on a millisecond difference. As for the type of resistance training, although the meta-analysis showed sprint performance being independent of it, the difference almost reached significance with a p=0.06. Thus, it is important to note that the greatest effect sizes were seen with a combination of traditional resistance training and plyometric work. Moreover, the greatest effect sizes for intensity were seen with medium loads corresponding to 60-85% 1RM; but this relationship was not statistically significant (p=0.34).
Finally, training with more sessions per week was detrimental to sprint performance, as was using shorter rest periods. The former is likely due to inadequate recovery in the long-term that inhibited “gains”, while the rest-interval effects are likely because a greater rest time allows for strength maintenance through the session and thus greater strength adaptations.
Bottom line: sprint or speed? Then go lift.