The Role of Resistance Training in Distance Running

Transcription

1 Original article The Role of Resistance Training in Distance Running Philip Tan, BSc (Sports Science) Department of Sports Medicine, Changi General Hospital, Singapore Abstract The main determinants of distance running performance include V O 2 max, lactate threshold (LT), and running economy (RE). The conventional way to achieve improvements in these areas is through endurance training due to the principle of training specificity. Some physiologists believe that the addition of resistance training is beneficial to distance running in the form of injury prevention and preparing runners for pace surge and sprint finishes. To date, it is consistent among findings that resistance training does not improve nor compromise V O 2 max in trained distance runners while LT improvements are only found in untrained individuals. RE has been shown to improve significantly post resistance training possibly due to neuromuscular changes including a shortening of the stretch-shortening cycle and an increase in muscle stiffness. The primary purpose of this review is to understand the impact of resistance training on the various factors known to affect distance running performance and to recommend resistance training guidelines for the distance runner to adhere to. Keywords: endurance running, plyometrics, running economy, strength/power training Introduction In distance running, runners have traditionally focused their training on improving cardiovascular and muscle endurance due to the principle of training specificity, which indicates that improvement in endurance performance may be achieved most effectively through aerobic training. However, good evidence suggests that anaerobic work capacity may be a determining factor in performance for well-trained runners in the forms of hill climbs, surges in pace and sprint finishes 1. This would indicate the need to include strength training if elite performance is desired as strength training, in the form of resistance training, typically involves high loads (often near maximal) and low repetitions that enhances the anaerobic energy production and force capacity of those specifically recruited muscle fibres 2. Resistance training may also be beneficial in regard to injury prevention, based on the assumption that stronger tissues from resistance training sustain damage less often 3. Despite the supposedly beneficial role of resistance training in enhancing distance running performance, the addition of strength/power training in the prescription of training programme for distance runners is often an issue of debate among coaches. Such worry is due to the conflicting demands of each type of activity and the possible antagonism of the training responses they elicit 4. The contrasting physiological demands of strength and endurance training may lead to interference, meaning that the training effect for one type of training negates the other. Consistent findings from literature do reflect that concurrent strength and endurance training impedes strength development but not endurance training adaptations 5,6. It is also of particular interest how resistance training impacts the primary factors affecting distance running performance, namely maximum oxygen uptake (V O 2 max), the lactate threshold (LT) and running economy (RE) 7. Jeopardising any of these factors is likely to have a detrimental effect on the individual s performance outcome. Thus, the purpose of this paper is to examine the role of resistance training in distance running as it relates to V O 2 max, LT, RE and any other variables that may 183

2 Original Article impact running performance. Different types of resistance training will also be addressed, including circuit training, traditional heavy resistance training and explosive training in the form of plyometrics. For the purpose of this article, the generic term resistance training will refer to any training specifically designed to increase muscular strength, power, endurance and/or promote neural adaptations. Specific types of resistance training will be described throughout the paper. Maximum Oxygen Consumption (V O 2 max) V O 2 max refers to the highest rate at which the body can consume and utilise oxygen during aerobic exercise 8. Commonly known as aerobic power, it is well recognised as one of the main predictors of successful distance running performance 9, with athletes who perform well in endurance activities typically possessing high V O 2 max values. Thus, a goal of many distance runners is to improve V O 2 max and most choose to avoid resistance training for fear of hindering their performance due to the physiological adaptations occurring from resistance training. Resistance training may increase body mass, promote the use of non-endurance, fast twitch muscle fibres, or decrease the activity of oxidative enzymes, any of which may hinder distance running performance by negatively impacting relative V O 2 max 10. Resistance training may also result in a reduction in mitochondrial volume density or decrease in capillary density which can result in an individual s ability to deliver and/or effectively utilise available oxygen 6. However, studies seem to dispel the myth that resistance training will hinder aerobic performance, with all the endurance athletes studied performing resistance training without causing a reduction in V O 2 max 11,12. On the other hand, data also appears to be quite consistent across studies that improvements in V O 2 max as a result of resistance training are unlikely to happen in aerobically trained or untrained subjects 12,13. For example, a study by Hickson et al demonstrated that cycling and running performances, as well as V O 2 max were unaltered following a 10-week resistance training programme where a group of well-trained (V O 2 max = 60mL/kg/min) male subjects performed parallel squat, leg press and calf raise 3 times per week [3 5 sets x 5 Repetitions Max (RM)] 14. This is not surprising, considering that an acute bout of resistance training elicits oxygen consumption values of less than 50% of V O 2 max 15. In fact, an upper and lower body resistance training workout consisting of 8 12 exercises was shown to result in an average oxygen consumption that was similar to that of walking on a treadmill at about 6.4km/hr 16. This is hardly a substantial stimulus for improving aerobic capacity in all but most sedentary of people. Lactate Threshold Lactate threshold (LT) refers to the point during exercise where there is a sudden dramatic increase in blood lactate concentration 17. LT has been shown to be an important predictor of performance in distance running 8 as a runner with a high LT is able to run at a high percentage of V O 2 max before the lactate production rate exceeds lactate removal rate. Theoretically, resistance training would be able to improve an individual s LT. Following a resistance training programme, both Type 1 and Type II muscle fibres are capable of producing more absolute force; therefore the fibres would work at a lower percentage of maximum strength during endurance exercise, compared with pre-training. This decrease in effort may have resulted in a decrease in anaerobic energy production, resulting in a decrease in blood lactate concentration 18. The decrease in relative force production per fibre may also decrease blood flow occlusion, which may have an effect on lactate production and/or clearance. However, till date, only one study 18 has displayed positive results whereby the subjects experienced a 12% increase in LT following a 12-week circuit-type training programme which involved performing common resistance training exercises such as bench press, knee extension and leg press. Such a finding, however, can be attributed to the fact that in the study, the subjects were untrained and not involved in a regular exercise programme hence allowing greater room for improvement compared to a trained population. Thus, evidence from literature is clear that endurance-trained athletes would not improve LT as a result of resistance training 11,19. It should also be noted that resistance training does not hinder LT, suggesting that distance runners could include resistance training as part of their training regime without a concomitant decrease in LT

3 The Role of Resistance Training in Distance Running Running Economy and its associated neuromuscular changes Running Economy (RE) is defined as the energy demand for a given velocity of sub-maximal running, and is determined by measuring the steady state consumption of oxygen and the respiratory exchange ratio 20. Runners with good RE use less energy and hence less oxygen than runners with poor RE at the same velocity. Thus, performance can be improved through running a set distance at a higher velocity or being able to run longer at a set velocity. Resistance training has been shown to improve economy in distance-runners by an average of 5 8% with no deleterious effects to V O 2 max or running performance 21. This would translate to a 21% increased time to exhaustion (from min) during treadmill running at a speed corresponding to 100% V O 2 max 22 or 3.1% in 5km running performance (from min) in welltrained runners (V O 2 max of 68 ml/min/kg) 11. The potential mechanism for the improved RE could be neuromuscular based with greater muscle activity prior to and the initial phase of ground contact 23. A key component of RE is the ability to use the stretch-shortening cycle (SSC) during ground contact 24 with preparatory muscle function being an important function of the SSC. The SSC involves improved concentric force and rate of force development following an eccentric concentration when the lower limb joints flex on ground contact. The increase in preparatory muscle activity with higher running speeds was suggested to be a mechanism to tolerate higher impact loads, regulate landing stiffness and improve running economy 25. Greater duration of muscle co-activation of the bi-articular leg muscles during stance also contributes to the modulation of leg stiffness during running, which increases the utilisation of stored elastic energy at no additional metabolic cost 26. Improving this mechanism via resistance training that is highly explosive and rapid in nature decrease ground contact time and hence improving RE 27. Adaptations to the nervous system may allow better inter-muscular coordination of all relevant muscles, leading to greater net force 4. Muscular adaptations could also account for enhanced RE, as strength training could cause increased strength of the slow-twitch fibres 21, thus requiring less motor-unit activation to produce a given force. Mechanical efficiency, muscle coordination and motor recruitment patterns would hence be improved 4 and these improvements in the neuromuscular system would influence running style to enhance running mechanics. Additionally, improved mechanical efficiency and greater muscle coordination may allow for a reduction in relative workload 19. This combination of improved running mechanics and neuromuscular efficiency may result in a decrease in oxygen consumption, thereby improving economy 21. Muscle Fibre Conversion It has been well-documented that the common muscular adaptation that occurs with both resistance training and endurance training would be the increase in percentage of Type IIa muscle fibres at the expense of Type IIb fibres 28. Since Type IIa fibres are more oxidative than Type IIb, an increase would indicate an improvement in the oxidative capacity of the muscles, which theoretically, could lead to an improved distance running performance by increasing the capacity for aerobic energy production. Findings by Coyle, et al, however, refuted this, demonstrating that RE was unchanged throughout a period of detraining despite a large shift from Type IIa to IIb fibres. This would suggest that muscle fibre conversion has little or no impact on oxygen uptake or economy of motion 29. Effects of the different types of resistance training on distance running To fully understand the role of resistance training for distance runners, a discussion of the impact of the different types of resistance training is necessary. The most commonly debated area would be whether to utilise high-load (H-load) or high-repetition (H-rep) resistance training to enhance distance running performance. Coaches usually prescribe light load but high repetition (15 40RM) training to distance runners on the basis that such is good for muscle endurance and aerobic sports 30. Yet consistent findings from literature suggest that H-load training with loads at % of 1RM performed with rapid actions improves endurance performance instead 11,31. A recent pilot study comparing the effect of H-load against H-rep training on endurance 185

4 Original Article training demonstrated that H-rep is as effective as H-load resistance training in improving rowing performance 32. However, it should be noted that the subjects were rowers, not distance runners. Moreover, the authors also observed that H-load resistance training was more effective for the more highly trained while the novice rowers improved to a greater degree and responded more to the H-rep training compared to the H-load training. Such findings are consistent with the theory that pretraining status dictates the magnitude of potential adaptation 33 and that periodised training with adequate loads may result in optimal adaptations for those with a higher pre-training status 34. Circuit training, which involves a variety of resistance training exercises performed with minimal rest (approximately 30 seconds) between sets, has been shown to improve endurance performance, including distance running, in untrained individuals 35. The mechanisms behind the improvements in V O 2 max and LT are perhaps due to a high heart rate response (about 80% maximum heart rate) during exercises and the limited rest between exercises, resulting in higher than average lactate levels 18. However, no current evidence suggests that circuit training would improve performance in trained distance runners. On the other hand, traditional resistance training such as squats and bench press has been shown to improve both long-term endurance (time to exhaustion at 80% V O 2 max and short-term endurance (time to exhaustion at 100% V O 2 max in trained and untrained subjects following a period of heavy resistance training 14,21. A final type of resistance training involves explosive movements in the form of plyometrics. Literature has shown that the addition of plyometric training to a distance runner s training programme can increase running economy 12. This will be discussed in greater details later in this paper. While the evidence from studies is convincing that a variety of types of resistance training have potential benefits to distance runners, more research is needed before it can be concluded which form of resistance training, if any, is superior. Plyometrics Towards a better economy While RE has been improved in distance-runner using traditional strength training 12, literature evidence also suggests that explosive resistance training in the form of plyometrics may be more beneficial in increasing RE of trained subjects. A recent study by Saunders et al demonstrated a 4.1% improvement in RE in 15 highly trained (V O 2 max = 70mL/kg/min) distance-runners, who underwent 9 weeks of plyometric training (3 x 30 minutes per week) 36. Similarly, Spurrs, et al demonstrated that 6 weeks of plyometric training improved the RE of moderately trained ( V O 2 max= 55mL/kg/min) runners as well 37. As stated earlier, the mechanisms behind the improvement in RE through plyometric training may be due to neuromuscular changes including a shortening of the SSC and an increase in muscle stiffness, which aid to increase the recovery of elastic energy from the eccentric phase of muscular contraction during running. It is suggested that plyometric training improves the ability of the lower limb joints to act stiffer on ground contact, thereby reducing the delay between the eccentric and concentric contractions 37. This makes the SSC action more efficient during each footfall, leading to a more economical running style. Increased musculotedinous stiffness after plyometric training had also been recorded 36 and Dalleau et al demonstrated through a theoretical study on RE that increasing the stiffness of the propulsive leg provided a lower energy cost per footfall 38. This would imply that athlete with greater reactive strength are more economical on each stride. However, it is likely that an optimal level of stiffness exists for SSC performance 39, hence the trade-off between stiffness and running performance needs to be considered. Unnecessarily increased stiffness results in shorter stride length 40, and consequently in decreased running performance. Therefore, although resistance training has the potential to enhance distance running, care needs to be given to the structure of the training programme such that stiffness can be increased to the point at which it assists the rebound action but does not impede the stride length. Practical recommendations for the coach/clinician/athlete All athletes, regardless of the event distance, should undergo a thorough needs analysis prior to design of a resistance training programme such that the individual s strengths and weaknesses 186

5 The Role of Resistance Training in Distance Running Objective Training Load Table 1: A 4-phase resistance training plan for the distance runner. Phase 1: Active Rest Phase 2: Off-season Phase 3: Pre-competition Phase 4: Competition Recovery from competitive season. Aim at developing muscular endurance 1 2 sessions per week Develop basic strength in preparation for higher intensity resistance training during precompetition season 2 3 sessions per week Increase strength and power to improve running economy 2 3 sessions per week. Maintain strength and power At least 1 session per week 1 3 sets of repetitions at 50 70% of 1RM 1RM = 1 repetition maximum. 2 3 sets of 10 repetitions at 60 70% of 1RM 2 3 sets of 10 repetitions at 60 70% of 1RM 1 2 sets of 6 8 repetitions at > 80% of 1RM can be recognised. A common fault among coaches in their prescription of resistance training programmes for distance runners is that the resistance training tends to involve high repetitions at low intensities throughout the year, for fear that muscle mass may be unnecessarily increased and that heavy lifting may hinder V O 2 max. While a specific one programme fits all distances training plan is impossible, the resistance training should parallel the pattern of the running programme 41, whereby the off-season involves lowintensity high volume distance running and as the competitive season approaches, a higher quality and lower volume of interval training is performed. Choices of exercises should be both upper and lower body. Upper-body strength is needed for arm and symmetrical movements of the body during running while the runner needs develop lower limb strength, as the lower limbs are subjected to loads of 3 5 times body weight during ground contact for running 42. Plyometric training should begin with lower-intensity drills such as squat jumps and vertical jumps and progressing to more intense exercises such as drop jumps and bounds by the end of pre-season. Hence, a training table (Table 1) towards the periodisation of resistance training programme in hand with the distance running programme is still feasible 43. Finally, in an ideal situation, resistance and distance running training should be performed on separate days but this may be impractical for the runner as endurance training sessions usually take place every day. While little research has been conducted to examine the acute effects of strength training on endurance performance, studies 44 recommend that resistance training should be performed first with at least up to 8 hours of recovery duration between resistance and endurance sessions to avoid interference effects. Conclusion Although there are limited studies done on exploring the influence of resistance training on distance running performance, evidence across literature seems to suggest that resistance training may improve V O 2 max and LT only in aerobically unfit individuals but not for the trained distance runners as the stimulus is not intense enough to challenge the aerobic system of the athlete. But a common consensus to be drawn is, resistance training has never been shown to have a negative influence on distance running performance. It is, however, well-documented that various forms of resistance training especially in the form of explosive movement training such as plyometrics, are able to improve running economy and distance running performance. This is achieved through neuromuscular adaptation, including a reduced time of the SSC and/or increase in muscle stiffness. Finally, more future research should be done on the impact of resistance training on race time or time trial performance as V O 2 max, LT, RE and other characteristics for endurance performance, despite being valuable measurements, would mean very little without an improved race performance. References 1. Bulbulian R, Wilcox AR, Darabos BL. Anaerobic contribution to distance running performance of trained cross-country runners. Med Sci Sports Exerc. 1986;18(1): Laursen PB, Chiswell SE, Callaghan JA. Should endurance athletes supplement their training program with 187

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