Hill Sprints and Running Economy: Review (Part 2)

   As promised for this week's post -- more on hill sprint training and its potential to improve running economy. Below I have included tid-bits from my review of literature. Yes, the text may be a bit redundant, especially if you read last week's post, but that is the nature of a proposal. I hope this information allows us all to further evaluate the training's potential.

Chapter 2

Review of Literature

Introduction

...Research has shown running economy (RE) to be a critical factor in determining distance running performance in highly trained runners. (J. T. Daniels, 1985; Midgley et al., 2007; Noakes, 1988; Spurrs et al., 2003).  Further, research shows running economy can be improved with traditional heavy-weight resistance training and/or plyometric training (Jung, 2003; McCann & Higginson, 2008; Midgley et al., 2007; Paavolainen et al., 1999; Saunders et al., 2004a; Saunders et al., 2006; Spurrs et al., 2003). Yet, no research has studied the effects of added resistance specifically to the running gait on RE.  Midgley et al. (2007) suggests one way off adding resistance to the running gait is by running uphill.  Adding resistance to movement could potentially improve running economy through the same mechanisms as resistance training and plyometric training...

The Importance of Running Economy

Numerous studies have found RE and performance to be closely associated with one another (Jung, 2003; Midgley et al., 2007; Paavolainen et al., 1999; Saunders et al., 2004a).  RE may be  particularly important to highly trained runners because these athletes have similar VO2max values. In highly trained distance runners with similar VO2max values, differences in RE are likely to explain a large portion of the variability in performance times between elite distance runners.  Daniels (1985) reports running economy can vary by as much as 30% among runners with similar VO2max values.  Further, Noakes (1988) states, VO2max is a poor predictor of performance when considering athletes of similar ability and RE is a better predictor of running performance.  Many others also suggest that RE is better predictor of running performance than VO2max alone in runners with similar VO2max values (Costill, Thomason, & Roberts, 1973; Paavolainen et al., 1999; Spurrs et al., 2003).

Evaluating Running Economy

Running economy has been evaluated with different protocols using both treadmill and over ground running.  Saunders et al. (2004a) state that while treadmill running is slightly different from over ground running, it can still be a reliable indicator of a runner’s economy and RE on a treadmill is still highly correlated with over ground RE.  A major advantage of using treadmill running is that variables in the laboratory such as temperature, humidity, and wind can be controlled for.  Saunders et al. (2006) tested RE at three different steady state running speeds on a treadmill.  After a standardized warm-up the subjects completed three four minute long stages at 14, 16, and 18 km/h. O2 uptake (VO2) was measured in the final minute at each speed.  By testing VO2 at multiple speeds, Saunders et al. were able to evaluate whether a 9 week plyometric training program changed RE at the different speeds tested.  Interestingly, the improvements in RE at higher speeds (16 and 18 km/h) were greater than those observed at slower speed (14 km/h) and the change increased with each increase in speed. In this study, the only statistically significant change in RE was seen at 18 km/h.  A trend found showing greater gains in economy with increased velocity. While it would have been interesting to see whether the changes in RE continued to increase at speeds of 20 km/h and higher, Saunders et al. chose to stop testing at a maximal speed of 18 km/h. This speed was chosen because it is a steady state speed for the athletes. This means that there is a negligible contribution of energy from anaerobic metabolism.  Saunders et al. (2004a) also suggest that RE of highly trained distance runners be tested at speeds eliciting no more than 85% of VO2max to minimize energy contribution from anaerobic metabolism.  Spurrs et al. (2003) used a protocol similar to Saunders et al. (2006) to test highly trained runners, but utilized three minute stages, an incline of 1%, and speeds of 12, 14, and 16 km/h. Interestingly, the results were not consistent with those of Saunders et al.  Spurrs et al. found that largest change seen in RE was at the slowest speed of 12km/h. Paavolainen et al. (1999) used over ground running and a portable O2 analyzer. Pace was controlled using a “light rabbit” on the track and the athletes completed two five minute stages at 3.67 and 4.17 m/s (13.2 and 15.0 km/h). RE was calculated as VO2 over the last minute of each stage.  A major limitation of the study by Paavolainen et al. is having the resources such as an indoor track, a portable VO2 analyzer, and a “light rabbit” to conduct the study.  Mojock et al. (2011) evaluated RE in moderately trained female distance runners, having them run on a treadmill for 30 minutes at 65% VO2max.  RE was determined by measuring total caloric expenditure and VO2 over the thirty minute trial.  Obviously, a limitation to this protocol is the use of only one running speed. This protocol may accurately assess RE at that one speed, but as Saunders et al. (2006) have shown, changes in RE may vary at different running speeds.  By utilizing a protocol that tests RE at multiple speeds, the likelihood of finding a statistically significant difference may be increased and the risk of committing an error decreased.... Others have also utilized performance time trials such as a 5000m run (Paavolainen et al., 1999).  Time trials may be a practical application assessing the training's effect on performance, but performance tests cannot isolate the variable of running economy.  A 5000m time trial would not be able to assess running economy (VO2) because a considerable amount of energy in a 5000m run between 13 and 16 minutes (18.8 to 23.1 km/h) comes from anaerobic metabolism.  Therefore improvements in 5000m time could be the result of improved VO2max, anaerobic capacity, or other variables involved in running performance.  Additionally, performance tests are limited in their ability to eliminate other variables that may also affect performance, e.g., temperature, wind, humidity, pacing.

Training Running Economy – Current Understanding

Running economy can be improved as a result of different training stimuli, and there are multiple mechanisms that influence RE. Altitude training, training in hot climates, resistance training and plyometric training have all been shown to improve RE (Saunders et al., 2004a).  Saunders et al. (2006) is one of many studies that found plyometric training to significantly improve RE.  The authors conclude that plyometric training may improve muscle power characteristics and/or increase the stiffness of the muscle-tendon system, enabling the body to better utilize stored elastic energy. This study is particularly important because it increased RE in highly trained, elite level distance runners.  Spurrs et al. (2003) and Paavolainen et al. (1999) have also demonstrated that that plyometric training improved RE.  A review by Jung (2003) investigated the impact of resistance training on RE,  and concluded that traditional heavy weight resistance training also improves RE – but the effect of long term resistance training has not been studied and may result in hypertrophy and weight gain which could negatively impact RE.

Could uphill running induce similar effects as resistance or plyometric training?

Jung (2003) states resistance training exercises that closely mimic a particular skill result in greater improvements in that particular motor skill. This is known as the rule of specificity.  Following the rule of specificity, performing exercises that most closely mimic the action of running should result in the most favorable improvements in running performance. Therefore, applying resistance to the running stride has the potential to improve running performance. Midgley et al. (2007) states that hills effectively add resistance to running and suggest that high-velocity running exerts similar training effects as resistance training in distance runners.  Potentially, by running at or near maximal velocities with the added resistance of running uphill, one could mimic the stimulus of resistance and/or plyometric training with a very specific application to the running gait and see improvements in RE.  However, no research exists investigating the effects of high-velocity uphill running on RE.  There is only speculation and anecdotal evidence from coaches and athletes on the effectiveness of running uphill intervals improving running economy. Some speculate it may improve anaerobic capacity, but is not applicable to training economy.  Arthur Lydiard was an advocate of hill running in the 1950’s and 60’s.  Lydiard’s athletes were well known for setting world records in 800 and 1500m and winning multiple Olympic gold medals.  Likewise, Jack Daniels, a world renown running coach and physiologist states in his book, Daniels’ Running Formula, that uphill running does indeed improve running economy (J. Daniels, 2005). Despite there being no scientific studies to support the theory, many coaches today still utilize uphill running; believing it strengthens their runners’ legs and improves RE.

Summary

RE is a critical component of distance running performance. Plyometric and resistance training have been proven to effectively increase RE by improving muscle strength and power and also through stiffening of muscles and tendons improving elasticity.  Hills effectively add resistance to running and high-velocity running may induce similar responses in muscles and tendons as resistance training. Logically, high-velocity uphill running may possess the potential to improve RE.  To date, no research has investigated the effects of high-velocity uphill running on RE.

References

Costill, D. L., Thomason, H., & Roberts, E. (1973). Fractional utilization of the aerobic capacity during distance running. Medicine & Science in Sports & Exercise, 5(4), 248-252.

Daniels, J. (2005). Daniels' Running Formula, Second Edition: Human Kinetics.

Daniels, J. T. (1985). A physiologist's view of running economy. Medicine & Science in Sports & Exercise, 17(3), 332-338.

Foster, C., & Lucia, A. (2007). Running Economy. Sports Medicine, 37(4/5), 316-319.

Jung, A. P. (2003). The impact of resistance training on distance running performance. . Sports Medicine, 33(7), 539-552.

McCann, D. J., & Higginson, B. K. (2008). Training to Maximize Economy of Motion in Running Gait. Current Sports Medicine Reports (American College of Sports Medicine), 7(3), 158-162.

Midgley, A. W., McNaughton, L. R., & Jones, A. M. (2007). Training to Enhance the Physiological Determinants of Long-Distance Running Performance. Sports Medicine, 37(10), 857-880.

Noakes, T. D. (1988). Implications of exercise testing for prediction of athletic performance: a contemporary perspective. Medicine & Science in Sports & Exercise, 20(4), 319-330.

Paavolainen, L., Hakkinen, K., Hamalainen, I., Nummela, A., & Rusko, H. (1999). Explosive-strength training improves 5-km running time by improving running economy and muscle power. Journal of Applied Physiology, 86(5), 1527-1533.

Saunders, P. U., Pyne, D. B., Telford, R. D., & Hawley, J. A. (2004). Factors affecting running economy in trained distance runners. Sports Med, 34(7), 465-485.

Saunders, P. U., Telford, R. D., Pyne, D. B., Peltola, E. M., Cunningham, R. B., Gore, C. J., & Hawley, J. A. (2006). SHORT-TERM PLYOMETRIC TRAINING IMPROVES RUNNING ECONOMY IN HIGHLY TRAINED MIDDLE AND LONG DISTANCE RUNNERS. Journal of Strength & Conditioning Research (Allen Press Publishing Services Inc.), 20(4), 947-954.

Spurrs, R. W., Murphy, A. J., & Watsford, M. L. (2003). The effect of plyometric training on distance running performance. European Journal of Applied Physiology, 89(1), 1-7.

     In summary, resistance and plyometric training has been shown to improve RE. Hill sprints could potentially mimic the stresses of resistance/plyometric training, while maximizing specificity and minimizing hypertrophy. Of course, this is theoretical physiology -- and theoretically physiology will not hold much clout in academia.

     Take note of the differences seen in running economy at different speeds in the Saunders study from 2006. This study used a 9 week long plyometric training protocol with highly trained nationally and internationally competitive middle and long distance runners. RE was evaluated at 14, 16, and 18 km/h. They found that RE was significantly increased only at 18 km/h. This equates to a 5:22 mile. But perhaps the most interesting thing was the decrease in VO2 slope with increasing running speed after training. What this means is that as the speed running increased, greater changes in RE were observed. Of course, it would be interesting to see if the trend continued out to 20, 22, 24 + km/h. But... the major limitation to the RE evaluation (steady state VO2 at a certain speed) is that it has to be an aerobic pace to evaluate VO2. So, running at 18 km/h (5:22 mile), these athletes were able to supply all the energy they needed through aerobic metabolism -- this is also consistent with their lactate analysis.

     But, who knows -- If we were somehow able to evaluate RE at non-steady state VO2 paces (20+ km/h), would we see this decreased VO2 slope continue? If so, this type of training could be particularly important to elite level middle distance runners who often complete 5000m in 13:15 at a rate of 22.6 km/h or 800m in 1:45.0 at 27 km/h. But even today, most major marathons are completed in under 2:08 which is 19.8 km/h -- faster than was tested in this study.

     Finally, the decreased VO2 slope after training is consistent to the findings of Cavagna (1964), who concludes that elastic mechanisms prevail at higher speeds.

     In the end, we have no studies to say whether or not hill sprint training improves running economy. We do have anecdotal evidence to suggest running hills improves running performance -- in the past and present some of the greatest coaches and athletes have incorporated some sort of hill training into their regime. I also do hill sprints, and have my athletes perform them. Why? Maybe it improves running economy by improving power/recruitment, maybe it improves lactic capacity (one's ability to create lactate). Either one, or a combination of the two could lead to an improvement in performance. And theoretically...

     This leads me to my next post: Next week I hope to discuss topics like lactate, lactate threshold, acidosis and why lactate capacity/threshold training is crucial to middle and long distance running performance from 800m to the marathon.

Feel free to leave me a question or comment. I'll need some topics for future blog posts...