Self-optimisation: The interaction between running biomechanics and running economy

I would like to welcome Isabel (Izzy) Moore to the Biomechanics blog. Izzy is a lecturer in Sport and Exercise Medicine at Cardiff Metropolitan University. I only know Izzy via the online world, but have had some great discussions with her via email and Skype about running mechanics and performance. Izzy has fantastic knowledge on this topic, having completed her PhD at Exeter University where she looked at running biomechanics and physiology, with an interest in understanding how running performance is improved or optimised. This has led her to more recently begin exploring the concept of running retraining in both the performance and injury management fields. In this blog, Izzy discusses her own and others work related to the self optimisation of running economy. This is exciting research, and I am even more exited about what future outputs will surely come in this field, particularly from Izzy. Feel free to post questions/comments here or on twitter using Izzy’s twitter handle. Over to you Izzy ……….

Running economy is a key indicator of long distance running performance. Running economy is defined as the rate of oxygen consumed at a given steady-state speed. If an individual consumes less oxygen than another individual at a given speed, they have a better running economy. Improving your running economy has two effects, either you can run further before reaching exhaustion or you can run faster for the same oxygen cost. A number of factors determine an individual’s running economy (see Saunders et al. [1]), one of which is running biomechanics or technique.

Self-optimisation of running economy

Early work by Cavanagh and Williams [2] identified that trained runners produce stride lengths that are near to their mathematically optimal stride length (i.e. they run with stride lengths that result in the lowest possible oxygen consumption). Later work looking at step rate (stride frequency) supports these findings, and also indicates novice runners have a step rate much slower (8%) than their optimal [3]. Figure 1 highlights the differences in stride frequency and running cost (‘economy’) between novices and trained runners.

Self optimising stride frequency

Figure 1 Individual differences (selected-optimal) in stride frequency (A) and running cost (B) for novice (left) and trained runners (right) on both (black and grey bars) test occasions. RCsel and RCopt, respectively, are the running costs at self selected stride frequency (SFsel) and at the stride frequency where running cost was minimal (SFopt). X denotes that optimal stride frequency and, consequently, optimal running cost could not be established in these five trials [3].

Considering the above findings, it is clear that runners can self-optimise or fine-tune the way they run, minimising the oxygen cost of running. Importantly, it appears that this self-optimisation takes time, requiring individuals to build up greater experience and exposure to the stimulus of running.

To specifically examine whether exposing novice runners to running led to self-optimisation, I conducted a study to investigate whether a 10 week running training programme could improve running economy and alter running biomechanics. The training programme was a gradual running programme that involved periods of running and walking during the first few weeks and eventually resulted in participants being able to complete 30 minutes of continuous running at the end of 10 weeks.

During 10 weeks of training, an 8% improvement in running economy, and several changes in lower limb biomechanics (kinematics and kinetics) occurred [4, 5]. What was evident was that biomechanics during propulsion appeared to be important to improved running economy. Specifically, the runners generated greater propulsive force (horizontal force in the direction of the run) and produced greater knee flexion and less ankle plantarflexion at toe-off following the 10 weeks of training (Figure 2). Importantly, this change in the alignment of force and leg orientation was correlated with improved running economy [5].

More horizontal push off

Figure 2 Differences in knee angle and ankle angle at TO (toe-off) between before and after measurements. Pre refers to baseline running biomechanics and post refers to running biomechanics after ten weeks of running whereby beginner runners improved their RE and altered their running [4].

Previous work has highlighted that generating propulsive force is metabolically demanding [6, 7]. Consequently, improving the way runners push-off from the ground could have large implications not just for their running economy, but also their running performance. In my previous work it seems that runners were able to improve their push-off by positioning their lower limb to facilitate a more horizontal push-off. This creates better alignment between the resultant ground reaction force vector and the longitudinal leg axis (vector between the ankle and hip) at the time of peak propulsive force (Figure 3).

Alignment of ground reaction force 2

Figure 3 Resultant ground reaction force (black arrows) and leg axis (white arrows) vectors at time of peak braking and peak propulsive force, pre and post training programme.

Can running economy be improved through running retraining (coaching)?

The question that most want to know the answer to is whether or not an economical running technique can be taught. Unfortunately, the answer is not a simple one and has rarely been investigated well. Firstly, most research has used acute running retraining interventions, and almost always, such acute changes to running technique are found to be detrimental to running economy [8, 9]. Short to mid-term interventions (5 to 12 weeks) have also tried to teach runners to run economically. However, these have not been successful and all have methodological issues such as, inadequate calculation of optimal stride length [10] or basing changes on a theoretical optimal, rather than evidence based, running technique that tries to alter numerous biomechanics at the same time [11]. Furthermore, the long-term effect of running retraining on running performance and economy is unknown. An important point to make is that altering an individual’s running technique should be done with caution as initially performance may drop, due to the worsening of running economy. Therefore, whilst it could be argued that trying to increase a novice runner’s step rate may be beneficial for their running performance, it is likely that in the initial stages running economy would become worse. However, attempting to increase step rate over several weeks may lead to improved running economy and, potentially improved performance – perseverance is needed.

The second reason why the answer is not a simple one is because self-optimisation is likely to be a subconscious process relating to minimising the effort required to run. The ‘effort’ of running is likely to be affected by numerous factors, therefore running technique must vary from person to person. For example, we know that reducing the oxygen cost of running and the muscular activity associated with running have a large influence on running economy [12], but effort will also involve elements such as, stress, anxiety, pain and fatigue. Additionally, the structural alignment or available range of motion will also impact on a runner’s most economical technique.

Instructing runners to alter their running technique in someway is also a cognitively demanding activity, hence why running retraining interventions targeting injury symptoms start with only a few minutes of instructions in the first instance [13, 14]. Therefore, altering a runners technique is a hard process for the runner themselves, which some may struggle with. So, whilst runners may want to push themselves to train harder, faster, for longer or more often (e.g. increasing distance, pace and/or frequency of runs), they do not want the way they run to be hard – that should be the easy part!

Summary

Self-optimisation is believed to be a physiological process that occurs as runners acquire greater running experience. Consequently, trained runners appear to have a more economical running technique than novice runners. A short intervention has shown that only 10 weeks of running exposure can lead to novice runners self-optimising their running technique and improving their running economy. In particular, propulsive biomechanics including more knee flexion and less ankle plantarflexion at toe off were associated with improved running economy. However, there are likely many other biomechanical factors which contribute to running economy, something I am currently formally reviewing – watch this space.

Self-optimisation is likely to be a subconscious process linked to the effort of running. Therefore trying to alter an individual’s running technique through instructions may actually be detrimental to running performance in the initial stages due to the high cognitive demands involved and unfamiliar feeling of a new running technique. However, the longitudinal effect of using instructions to alter running technique on running performance is currently unknown. It is important to note that many factors play a role in determining whether a running technique is economical or not. For example, anthropometrics, previous injury history, shoe degradation, strength and terrain will also play a role. Consequently, prescribing a ‘one size fits all’ economical way of running is unlikely to be the answer due to the interplay of modifiable and unmodifiable factors.

References

1. Saunders PU, Pyne DB, Telford RD, et al. Factors affecting running economy in trained distance runners. Sports Med. 2004;34:465-85.

2. Cavanagh PR and Williams KR. The effect of stride length variation on oxygen uptake during distance running. Med Sci Sports Exerc. 1982;14:30-5.

3. de Ruiter CJ, Verdijk PW, Werker W, et al. Stride frequency in relation to oxygen consumption in experienced and novice runners. European Journal of Sport Science. 2013;doi: 10.1080/17461391.2013.783627.

4. Moore IS, Jones AM and Dixon SJ. Mechanisms for improved running economy in beginner runners. Med Sci Sports Exerc. 2012;44:1756-63. doi: 10.1249/MSS.0b013e318255a727.

5. Moore IS, Jones AM and Dixon SJ. Reduced oxygen cost of running is related to alignment of the resultant GRF and leg axis vector: A pilot study. Scand J Med Sci Sports. 2015;doi:10.1111/sms.12514

6. Chang YH and Kram R. Metabolic cost of generating horizontal forces during human running. J Appl Physiol. 1999;86:1657-62.

7. Chang YH, Huang HW, Hamerski CM, et al. The independent effects of gravity and inertia on running mechanics. J Exp Biol. 2000;203:229-38.

8. Tseh W, Caputo JL and Morgan DW. Influence of gait manipulation on running economy in female distance runners. J Sports Sci Med. 2008;7:91-5.

9. Egbuonu ME, Cavanagh PR and Miller TA. Degradation of running economy through changes in running mechanics. Medicine & Science in Sports & Exercise. 1990;22:S17.

10. Messier SP and Cirillo KJ. Effects of a verbal and visual feedback system on running technique, perceived exertion and running economy in female novice runners. J Sports Sci. 1989;7:113-26.

11. Dallam GM, Wilber RL, Jadelis K, et al. Effect of a global alteration of running technique on kinematics and economy. J Sports Sci. 2005;23:757-64. doi: 10.1080/02640410400022003.

12. Miller RH, Umberger BR, Hamill J, et al. Evaluation of the minimum energy hypothesis and other potential optimality criteria for human running. P Roy Soc Lond B Bio. 2012;279:1498-505. doi: 10.1098/rspb.2011.2015.

13. Willy RW, Scholz JP and Davis IS. Mirror gait retraining for the treatment of patellofemoral pain in female runners. Clinical Biomechanics. 2012;27:1045-51. doi: http://dx.doi.org/10.1016/j.clinbiomech.2012.07.011.

14. Noehren B, Scholz J and Davis I. The effect of real-time gait retraining on hip kinematics, pain and function in subjects with patellofemoral pain syndrome. Br J Sports Med. 2011;45:691-6. doi: 10.1136/bjsm.2009.069112.