Strength training resulted in:
- 2-4% increase in time-trial performance.
- 5-7% increase in VO2 max.
- 4-7% increase in running economy
Endurance running performance is primarily dependent on a variety of physiological, psychological and biomechanical factors that intricately interact to sustain continued running locomotion at an effective pace.
In such prolonged-duration sport, even the smallest of improvements can go a long way. Considering this, previous research papers have suggested strength training to provide small increases in running efficiency which can transfer into substantial improvements in running performance.
Therefore, we investigated this by performing a systematic review and meta-analysis, involving nine research papers which examined the effects of strength training on endurance running performance. We also aimed to explore some of the specific aspects of this literature which are not well-understood, such as different training protocols and the neurological and muscular responses produced.
Methodology and Studies
We performed electronic database searches to extract the most valid and up to date studies in this area.
A strict inclusion criterion was followed to ensure the best quality studies were used.
To name a few, this inclusion criteria included: a PEDro score (study quality rating) >4, published >2002 and must be peer-reviewed using a control group.
Runs were analysed from 2km-10km, using ‘trained runners’ only. The strength training interventions were performed concurrent with regular endurance training. Marathon-based studies were not included due to being classed as an ‘ultra-endurance run’.
As a result of this process, we ended with 9 studies in our analysis (see figure 1)
In accordance with the standardised mean difference (SMD) and p-values across all 5 analysed studies, the results of this meta-analysis report a trivial, non-significant improvement (-0.061, P>0.05) in endurance running time-trial performance from the strength training interventions.
Furthermore, the results of this statistical analysis suggest a trivial significant improvement (0.239, P<0.05) in VO2 max from strength training interventions from the 6 used studies.
Study heterogeneity was 99.115%, meaning the differences in outcomes between each study was too great for analysis.
In an attempt to investigate the specific cause of the heterogeneity, each study was individually, observationally analysed in order to find outliers in study variance, in which no outliers were found. Thus, likely due to differences in run distance, the findings of this meta-analysis are limited and are therefore not discussed.
The results of the present observational systematic review determine that strength training can significantly improve endurance running time-trial based performance, with improvements between 2-4% commonly reported.
To put this into perspective, the 3.62% improvement in 5k run time found in Karsten et al (2016) would be enough to drop Mo Farah from first place (13:03) to last place (13:49) at the Rio 2016 Olympics. Therefore, while this percentage difference appears small at first glance, it can make all the difference!
There are also significant improvements in VO2 max following strength training, which is an important finding. Not only is VO2 max the most important contributor to endurance running performance, it is also one of the most fundamental measures of physiological health, with those having a higher VO2 max being at a significantly lower risk of all-cause mortality (Strasser & Burtscher 2018).
The results of this systematic review also show that these improvements in endurance performance can be achieved through both traditional heavy weight training and plyometric training. Additionally, as seen in table 2, various training protocols of differing intensities, rep/set ranges and exercises have successfully elicited similar benefits, suggesting runners to have freedom in successfully implementing strength training of different kinds.
Why is strength training so effective?
The key to the success of strength training is its ability to improve ‘Running Economy’.
Running economy can be defined as the steady-state VO2 required at a given submaximal speed and when improved, is reported to result in more efficient energy usage at submaximal intensities, sparing vital energy (glycogen) stores for crucial stages of the endurance run (i.e a sprint finish).
The importance of running economy in endurance running performance is highlighted in an early study from Conley & Krahenbuhl (1980) who analysed highly trained athletes with similar VO2 max levels in a 10-kilometre run and reported running economy to explain 65.4% of the variability in performance.
There are many ways in which strength training improves running economy:
Firstly, lower limb muscle and tendon stiffness is a proposed adaptation from strength training that enhances endurance running economy. Specifically, at the start of the ground contact phase in a running stride, elastic energy is stored in the muscles, ligaments and tendons. During the second part of the ground contact phase, a partial return of this stored energy occurs, which results in improved energy expenditure efficiency and enhanced mechanical output. Thus, strength training increases muscle and tendon stiffness, resulting in increased utilisation of this stored elastic energy and increased contraction output during a running stride (Vikmoen et al 2016).
Additionally, strength training improves the stretch-shortening cycle. The stretch-shortening cycle is the body reactivating the (lower-limb) muscles to absorb force and reduce the amount of eccentric contraction, resulting in an increased concentric contraction which enhances the final push of phase of a running stride (Vikmoen et al 2016).
Other muscular changes that have been reported to occur with strength training are adjustments to fibre type as strength training is suggested to lead to increases in the proportion of more fatigue-resistant type IIA (ultra-fast twitch) fibres compared to type IIX (fast-twitch) fibres while reducing the reduction of type I fibres which are crucial for endurance running (Staron et al 1994., Sale et al 2003).
Strength training can also result in substantial neural adaptations that are beneficial to running economy and performance. Specifically, strength training can elicit a significant increase in the rate of activation of motor units (Millet et al 2002).
Motor units are comprised of a motor neuron and all of the muscle fibres it innovates; thus, an increased rate of motor unit activation enhances the muscular contraction.
Essentially, as a result of these discussed physiological changes, there is an increase in force-generating capacity when running. As a concequence of this, the runner only needs to use a smaller percentage of their total capacity to carry their body weight when running, thereby increasing running efficiency and therefore performance.
As running economy is improved, it is also important to consider that the longer you run, the greater the benefits of this improvement.
Types of strength training
Our findings show a significant increase in endurance running can be achieved through either dynamic heavy weight training or plyometrics.
Dynamic heavy weight training refers to traditional forms of strength training with external weight, such as squats, lunges, and calf raises. On the other hand, plyometrics is a more unconventional method, generally involving repeat bursts of maximal output jump-based movements.
As both methods appear to be effective, runners/running coaches have options in developing and integrating effective strength training programmes for endurance running performance.
Debunking the myth: ‘Strength training is bad for long-distance running’
Due to the inevitable increases in muscle mass, strength training was previously believed to be negative for endurance running due to carrying extra weight or through detrimental changes in capillary diffusion distances. While these are not far-fetched hypotheses, more recent research has debunked these ideas.
Looking at the studies in the present systematic review, only two of the nine studies found changes in body mass or limb girth, thus suggesting no negative effect from the increased muscle mass. This is believed to be due to an interaction between strength training and aerobic training blunting the hypertrophic response usually observed.
In regard to capillary changes, research from Vikomoen et al (2016) directly measured the hypothesis that strength training increases the diffusion distance between the capillaries and interior of the muscle cell and found no significant changes in capillaries around each fibre or capillaries related to the fibre area for both type I and type II fibres, thus rejecting this hypothesis.
Despite this, there is a potentially negative interaction as aerobic training appears to reduce strength gains, suggesting the utility of a well-designed training programme to separate aerobic training days from strength training days.
The present systematic review highlights the efficacy of strength training for endurance running performance, highlighted through consistent reports of significantly improved time-trial performance, running economy and VO2 max.
These results suggest runners should implement strength training into their routine in the form of dynamic weight training or plyometrics for 2 sessions per week, with flexible choices regarding sets, reps and exercise selection.
Strasser, B. and Burtscher, M. (2018). Survival of the fittest: VO2max, a key predictor of longevity. Front Biosci (Landmark Ed), 23(23), pp.1505-1516.
Conley, D.L. and Krahenbuhl, G.S. (1980). Running economy and distance running performance of highly trained athletes. Med Sci Sports Exerc, 12(5), pp.357-60.
Staron, R.S., Karapondo, D.L., Kraemer, W.J., Fry, A.C., Gordon, S.E., Falkel, J.E., Hagerman, F.C. and Hikida, R.S. (1994). Skeletal muscle adaptations during early phase of heavy-resistance training in men and women. Journal of applied physiology, 76(3), pp.1247-1255.
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Damasceno, M.V., Lima-Silva, A.E., Pasqua, L.A., Tricoli, V., Duarte, M., Bishop, D.J. and Bertuzzi, R. (2015). Effects of resistance training on neuromuscular characteristics and pacing during 10-km running time trial. European journal of applied physiology, 115(7), pp.1513-1522.
Karsten, B., Stevens, L., Colpus, M., Larumbe-Zabala, E. and Naclerio, F. (2016). The effects of sport-specific maximal strength and conditioning training on critical velocity, anaerobic running distance, and 5-km race performance. International journal of sports physiology and performance, 11(1), pp.80-85.
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Vikmoen, O., Raastad, T., Seynnes, O., Bergstrøm, K., Ellefsen, S. and Rønnestad, B.R. (2016). Effects of heavy strength training on running performance and determinants of running performance in female endurance athletes. PloS one, 11(3), p.e0150799.