Andrew Hamilton looks at recent research suggesting that runners need to regularly check the cushioning on their running shoes - even if they feel okay! MORE
Research review: Running shoe choice: a weighty matter
Sports Performance Bulletin looks at new research on how running shoe weight impacts running economy and performance
When it comes to running performance, a key factor that needs to be taken into consideration is muscular efficiency. Muscles that work very efficiently are able to generate more propulsive force while requiring less energy (and therefore less oxygen). This internal type of efficiency is referred to as ‘muscle economy’. Economy refers to how efficient the muscles are (in terms of oxygen usage) at producing force during sub-maximal exercise (ie not flat out). The better the economy of your muscles during exercise, the less oxygen you need to use to propel yourself along at a given speed.
The importance of economy
Why is maximizing economy so important for maximizing race performance? Well, studies unequivocally show that elite athletes have much higher levels of muscle economy than their amateur or recreational counterparts. In other word – muscle economy and high levels of endurance go hand in hand. One study of collegiate cross-country team members discovered that just two factors – maximum aerobic capacity (VO2max) and running economy – could account for 92% of the variance in performance during an 8000m race(1). Also, running economy, like VO2max, has been used to estimate marathon pace in elite runners(2).
Another study comparing elite Eritrean runners with elite Spanish found that the Eritreans comfortably outperformed their Spanish counterparts despite having lower maximum oxygen uptake values. The reason? Testing on both groups revealed that the key physiological difference was the exceptional running economy of the African runners; at 21kmh (13.0mph), the Eritreans needed to consume just 65.9mls of oxygen per kilo per kilometre – compared with 74.8mls of oxygen for the Spanish runners (see figure 1)(3).
Figure 1: Oxygen consumption per kilo per kilometre at 21kmh
The Eritrean runners’ superior running economy meant they needed 13.5% less oxygen per kilo of body weight to maintain a marathon pace. This explained much of their performance advantage over their Spanish counterparts.
Running economy is influenced by multiple factors, most notably metabolic, cardiorespiratory, neuromuscular and biomechanical factors – all of which can be modified over time through training, leading to improvements in running economy. However, running economy can also be modified acutely through interventions such as changes in footwear. This is an area of increasing interest, especially after the recent sub-2-hour marathon attempts in which technological advanced footwear played a pivotal role(4,5) (for a more detailed discussion of what it will take to run a sub-2hr marathon, see this article). The key point here is that if a running shoe can decrease the energy cost of running, an athlete will be able to maintain faster running speeds at any given metabolic rate, which is essential when trying to attain a new PB, or trying to break the marathon world record!
Previous studies on shoe weight and running economy have shown an increase of around 1% in the energy cost per 100 g of added mass per shoe for a given sub-maximal pace(6), leading to a performance reduction of 2% during a 5-km time trial(7). In other words, heavier shoes, increase oxygen demand per mile run, leading to slower speeds. However, there’s little data on how shoe mass impacts performance when running speeds approach or reach vVO2max – the running speed achieved at maximal oxygen uptake (when there is no more oxygen availability). This is important because these are the kinds of intensities many runners will reach during at least some parts of a race.
To try and answer this question, a new study by an international team of sports scientists has assessed the effects of adding shoe mass on running economy, gait characteristics, neuromuscular variables and performance in a group of 11 trained runners(8). In this study, the runners completed four trials, each separated by at least seven days. The first session consisted of a maximal incremental test where the second ventilatory threshold (VT2) was calculated. VT2 is the exercise intensity at which speaking becomes difficult to achieve with the exception of one or two-word statements, and is also correlated to the point at which fatiguing lactate begins to rapidly accumulate in the bloodstream (see this article for more info). In addition, the speed associated with each runner’s VO2max (vVO2max) was calculated. In the next three sessions, the runners’ running economy at 75, 85, and 95% of the second ventilatory threshold (VT2) and their times to exhaustion (TTE) at vVO2max were assessed in three identical trials wearing the same shoe design. However, each trial differed as follows:
- Control – no added weight the shoe
- Shoe with 50 weight added
- Shoe with 100g weight added
During each trial, the runners’ biomechanical and neuromuscular variables (gait pattern), blood lactate levels and energy expenditure were measured and the results compared.
The key findings were as follows (also see figure 2):
- Running economy when running at 85% and 95% of VT2 speed significantly worsened with the increment of shoe mass.
- Heart rates rose when shoe mass increased at all speeds (75%, 85% and 95% of VT2).
- At maximum speed (vVO2max), the time to exhaustion was significantly (22%) longer in the control condition (no weight added) than when 100g was added (see figure 2B). Adding 50g also resulted in a shorter time to exhaustion although the difference wasn’t large enough to be considered significant.
- Running gaits in the runners did not seem to be affected by adding extra weight.
Figure 2: Running economy and shoe weight
A = Running economy at 75, 85, and 95% of the VT2. B = time to exhaustion test performance. Bar graphs represent average values; dots joined by lines represent individual runners.
Practical implications for athletes
It’s long been known that increasing shoe weight increases oxygen demand at a given sub-maximal pace, thereby reducing running economy. What this new research shows is that at higher speeds, when athletes are working near or at their physiological limits, the impact of shoe weight on performance is surprisingly significant.
In terms of practicalities, this suggests that where possible, switching to a lighter pair of running shoes for race days could reap significant rewards, especially when the weight savings exceed 50 grams per shoe. There’s a big caveat however; lighter shoes tend to offer less cushioning and support, which means that athletes need to choose a lighter shoe that is still able to offer adequate protection. Running a race in a shoe that doesn’t might knock a few seconds off a PB but athletes will feel short changed if it leads to an injury! Another caveat is that any lightweight ‘racing’ shoe still needs to be tried, tested and broken in before an event. The shoes should therefore be trialed out in a couple of fast tempo training runs first to ensure that they are fit for purpose. Finally, heavier runners, or recreational/novice runners are likely to improve running economy more through training than switching to lighter race shoes. And being more prone to injury too makes the argument for the use of a lightweight racing shoe even harder to justify!
- J Sports Med Phys Fitness. 1991 Sep; 31(3):345-50
- J Physiol. 2008 Jan 1; 586(1):35-44
- Appl Physiol Nutr Metab. 2006 Oct;31(5):530-40
- Med 2019. 49, 133–143
- Sports Sci 2019. 00, 1–7. doi: 10.1080/02640414.2019.1633837
- Med 2015. 45, 411–422
- Sports Sci 2016. 34, 1740–1745
- Physiol 2020. 11:573660