A Literature Review done for my Masters in Sports Medicine (MsSpMed), University of Queensland, Australia 2017

• Introduction
• Strength Training Types
• Results
• Discussion
• Markers of Performance
• Strength Diagnostics
• Time Trial Performance
• Running Economy
• VO2Max
• Possible Concerns of Coaches and Athletes
• BMI
• Injury Rates
• Additional Fatigue from Strength training
• Duration of Strength Training
• Preferred Type of Strength Training
• Practical Recommendations
• Conclusion
• References

Introduction

East Africans have dominated elite distance running for the past few decades and their success is frequently attributed to their superior running economy18. Running economy (RE) is the amount of energy expended by the runner when running at a given velocity. Traditionally,  measures such as maximal oxygen uptake (VO2max) and lactate threshold (LT) have been used in the laboratory to predict running performance. However, elite runners with similar VO2max but with different running economies can have drastically different running performances.

It has been shown that adult endurance athletes who participate in endurance training for several years seem to reach an apparent ceiling of VO2max and running performance19 . In these athletes, strength training could be a possible modality to enable further improvements in running economy. This theoretical improvement is thought to occur through several mechanisms such as neuromuscular adaptations (including musculotendinous stiffness, motor unit recruitment and synchronisation, and neural inhibition), which allow more forces to be developed during each running stride.

In the bid to compete with the elite East Africans, one would expect elite runners from other countries to pick up any novel training modality that would result in even marginal improvements in RE. However, for unknown reasons, strength training is a controversial subject among runners. A survey at the 2008 US Olympic Marathon trials found that top American marathoners “included little strength training in their training programmes… and nearly half of the runners did not do strength training at all”17. This may be due to several misconceptions that coaches and athletes have towards strength training.

Strength Training Types

There are 3 main forms of strength training: maximal-strength (MS) training which involves high load, low velocity movements; explosive strength (ES) training that involves high velocity movements with medium to high loads and finally, reactive-strength (RS) training that involves low load high velocity exercises. Each of them target different aspects of strength in muscles. MS targets maximal force development, ES improves rate-of-force development and maximal power output while RS increases musculotendinous stiffness and the stretch-shortening cycle function of muscles.

In addition, a fourth type of strength training involves body weight movements with minimal equipment such as a Swiss Ball. It is not uncommon for runners to engage in these exercises after their runs due to their ease and efficiency without visiting a gym. These exercises focuses mainly on building stronger core muscles, which is argued to provide better core stability during running and thus improve athletic performance and reduce risk of injury28.

The aim of this literature review is to determine the effects of strength training on running performances, specifically in RE and other endurance- specific assessments, as well as to address common misconceptions that coaches and athletes have towards strength training.

Results

A search was performed using PubMed to identify studies that assessed the effect of strength training on running performance in distance runners. 14 recent studies were elicited and several performance markers were used to compare changes in running performance. These include Running Economy (RE), strength diagnostics tests (both open and closed chain exercises), maximal volume of oxygen uptake (VO2max) and time trials over various distances. Most of the studies were randomised trials which had the control group perform only run training while the experimental group included strength training in their regime. 3 of the studies7,9,14 went a step further to compare “running training only” with two different forms of strength training to find out if different types of strength training yielded different benefits.  The results are summarised in Table 1.

Discussion

Results of the studies reviewed strongly suggest positive effects of strength training on running performance, especially in running economy. This discussion will begin by explaining each marker of performance and its weaknesses identified. Thereafter, I will address some of the concerns that coaches and athletes have towards strength training with results from this literature review.

Markers of Performance

Strength Diagnostics

It is evident from the studies that strength training improves muscle force-velocity characteristics. The running movement requires hip, knee and ankle muscles to work in unison to produce force against the ground. Thus, a valid strength test ideally should measure force in the same way, through closed-chain, multi joint exercises such as squats or jump squats. However, some studies2,3,8,13 in this review utilised open-chain, isolated exercises such as knee extension to measure strength which may not accurately correlate to strength performance in multi-joint movements such as that in running.

Future studies should utilise closed-chain, multi joint exercises to measure improvement in strength.

Time Trial Performance

In this review, it is found that strength training can significantly improve 2.4km, 3km and 5km time trial performances in runners2,3,7,11. It can be argued that a time trial carries high ecological validity as participants are in their natural running environment (outdoors) and attempting to complete a fixed distance as fast as they can. However, it is important to note that elite endurance racing success is not just determined by the average pace at which a runner runs over a set distance, but is also affected by racing and pacing strategies. Therefore, time trials may not be a ‘true’ reflection of racing performance15. To overcome this limitation, time trials can be carried out  together with analyses of other performance markers, such as RE to give a more complete picture of the effects of strength training on running performance, as done so by the studies reviewed.

Future studies should also evaluate time trial results with other performance markers to provide a better overall assessment of running performance.

Running Economy

There appears to be a clear trend1,2,3,4,5,6,7,9,10,11,12,14 of an improvement in RE with the addition of MS and RS type strength training into the athlete’s training regime. Some studies did not find any improvement in RE, possibly due to their methodology. For example, Fletcher et al.8 only focused on strengthening the calf muscles which contribute less to the running motion as compared to the hip and thigh muscles. Stanton et al.10 only did core strengthening exercises which may contribute to running performance as much as leg muscles. These findings support the well accepted theory that runners with poor economy may lack musculotendinous stiffness and will benefit from strength training to improve the muscle’s ability to rapidly absorb and utilise elastic energy produced during ground contact20. However, whether strength training improves RE universally  among all runners is still not conclusive.

Firstly, it appears that improvements in RE is velocity-specific. Spurrs et al.3 found a 6.7% and 6.4% significant improvement at speeds of 12km/h and 14km/h respectively but only a 4.1% improvement at 16km/h. Similarly, Saunders et al.4 only found significant improvement at 18km/h in elite international marathoners with no change at 14 and 16km/h. This suggests that the improvement is highly specific at the pace that runners race at, supporting the theory of adaptation specificity21. Thus, it may be possible that studies that do not find positive results have not studied runners running at their specific race velocities. Future studies should take this into consideration when assigning pace and velocities in the assessment of RE.

Secondly, the two genders appear to respond differently towards strength training. Barnes et al.9 found that there was significant beneficial effect on competition performance for females but a possible negative effect for males. Some studies had subjects of both genders but they either did not compare the effects between the genders or did not find any difference among the two.

Knowledge of these differences will impact training practices among coaches and athletes and more studies need to be done to identify them.

VO2Max

Current literature supports that strength training does not impact maximum oxygen uptake (VO2max)  in runners, with none of the studies reviewed showing a positive impact. This confirms the hypothesis that the improvement in RE is due to other mechanisms rather than improved cardiovascular fitness.

Possible Concerns of Coaches and Athletes

BMI

A  reason given by coaches and athletes who avoid strength training is the fear of putting on weight. None of the studies reviewed found a significant increase in BMI after implementation of the strength training program. This suggests that strength training can be considered a viable way of improving running performance without the fear of gaining weight.

Injury Rates

Risk of injuries are a definite concern for coaches and athletes when undertaking a strength training regime. Some argue that RS training in the form of plyometrics which involves jumping from relatively high surfaces appears to increase the risk of injuries. On the contrary, plyometrics have been advocated as a preventive injury strategy22,23 and even as a rehabilitation tool24. However, none of the studies mentioned any drop out rates except for Berryman et al.7 in which 7 participants dropped out but none of them stated injuries from strength training as a reason. Future studies should consider recording injury rates in the strength training group.

Additional Fatigue from Strength training

Another concern that coaches may have is that strength training may lead to additional fatigue for athletes such that they are unable to focus their energies on running itself which they believe is key to the athlete’s performance. The ideal doseage of strength training for elite runners is debatable,  however, it is likely that a short program done twice a week may be beneficial for the athletes’ running performance. At the same time, this would minimise the risk of nonfunctional overreaching which can occur when training load is increased and monotonous27. Future studies can include fatigue monitoring such as that through the measurement of daily heart rate variability to monitor additional fatigue in the experimental group.

Duration of Strength Training

The average intervention period in this review was approximately 8 weeks, with the longest being a 14 week programme12. A few studies examined the long term strength adaptations in athletes from strength and power sports over a period of up to 2 years25 . Unfortunately, none included distance running. Future research in this area can consider long-term strength interventions over 12 – 18 months and subsequent running performance.

Preferred Type of Strength Training

Current literature is not conclusive with regards to which type of strength training yields the most benefits for runners. Based on the studies reviewed, all 3 main forms of strength training – maximal strength, explosive strength and reactive strength – provide beneficial effects on running performance. There is limited literature on the effectiveness of core strengthening with body-weight exercises or those aided by equipment such as the Swiss Ball. Moreover, some studies13 were not distinct in the selection of exercises and had a mixture of strength training from the different domains. In the studies that compared different strength modalities7,9,14, no significant differences between them were elicited.

Future studies can consider a more distinct differentiation in the selection of exercises in the experimental arms to compare the effectiveness of various forms of strength training.

Practical Recommendations

In view of the current literature, it may be advisable for runners to engage in some form of strength training to improve running economy, be it in the form of MS, ES or RS training. Two sessions per week appears to be sufficient to achieve desired effects over a 6-10 week period. However, it is advisable to work with a specific strength and conditioning coach to ensure proper exercise techniques to reduce the risk of injuries. In addition, it may be helpful to implement strength training at the end of the competition season to avoid overtraining16.

Conclusion

Recent research on runners indicate that strength training can be successfully undertaken to enhance running performance. Teams and coaches should consider implementing strength training programs for their athletes, especially in the off season.

References

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2. Paavolainen L, Hakkinen K, Hamalainen I, Nummela A, Rusko H. Explosive-strength training improves 5-km running time by improving running economy and muscle power. Scandinavian Journal of Medicine and Science in Sports. 2003;13(4):272–272.
3. Spurrs RW, Murphy AJ, Watsford ML. The effect of plyometric training on distance running performance. European Journal of Applied Physiology. 2003;89(1):1–7.
4. Saunders PU, Telford RD, Pyne DB, et al. Short-term Plyometric training improves running economy in highly trained middle and Long Distance runners. The Journal of Strength and Conditioning Research. 2006;20(4):947.
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