Posts tagged running economy
Reducing Impact Forces In Runners
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In our previous blogs, we have described interventions designed to reduce the high rates of running related injuries. To date, our best Physical Therapy interventions include controlling training volume, concurrent strength training, and gait retraining. In our Boulder Physical Therapy practice we aim to reduce peak loading forces at foot strike in our runners. This can be achieved by increasing a runner’s forward lean (from the ankles) and stride length to reduce braking forces at the foot and ankle, as well as, reducing vertical oscillation in the flight phase of running. A recent article reviewed the use of real time biofeedback to reduce these braking forces in runners.

Napier and colleagues in the Journal of Orthopedic and Sports Physical Therapy utilized biofeedback in healthy, female runners with high rates of peak braking forces (2018). Each participant was provided with an 8 session gait retraining program aimed to increase step frequency and reduce step length. Basic cuing, such as “land softer”, can be used in this population to reduce the braking forces and in turn conserve energy for forward propulsion. Authors reported significantly reduced peak braking forces after the gait retraining sessions. In addition, these gait changes have been previously associated with increased running economy and performance.

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Impact of Running Shoe Wear on Running Economy
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In prior posts we have described the importance of running economy.  Runners with improved economy, similar to miles per gallon in a car, will be able to run at lower percentage of their VO2 max at a given intensity compared to a less economical runner.  Economical runners demonstrate improved performance in both training and competition.  In addition to mechanics, another frequently studied contributor to economy includes shoe wear.  Prior thoughts on lighter shoes being more economical and now being challenged in the research.

Cochrum and colleagues in the Journal of Strength and Conditioning Research examined the impact of foot wear on running economy among recreational distance runners (2017).  The authors had each runner run at 50 and 75% of their VO2 max barefoot, as well as, wearing minimalist and normal running shoes.  As expected when barefoot or in a minimalist shoe, runners choose a higher step frequency compared to the shoe conditions.  Surprisingly, the authors concluded running economy was not affected by shoe wear or barefoot conditions.  The authors recommend choosing footwear on a case by case basis instead of recommendations based on assumptions that one shoe is more economical than another.

Strength Training's impact on Running Economy

This week we posted on the benefits of strength training on cycling performance.  Specifically, how strength training improves our body's use of resources including oxygen and fuel to power us through our endurance workouts.  The more economical or efficient endurance athlete will be able to sustain a higher speed for a longer period of time than a less economical runner.  Research conducted in trained runners also shows the benefits of incorporating strength training along with endurance training. 

Authors conducted a review of the existing literature on the effects of strength training in trained runners (Balsalobre-Fernandez et al. J Strength Cond Res. 2016).  Subjects in this review were all well trained middle and long distance runners with VO2 max values >60 ml/kg.  A total of 5 randomized controlled trials were included in the review.  Participants used strength training 2-3 days per week for 8-12 weeks in addition to their endurance training.  Athletes trained at a 3:1 endurance to strength training ratio.   A large, beneficial effect was seen on running economy among athletes who performed both strength training and plyometric exercises.   

Runners are encouraged to work with a local, Physical Therapist to develop a strength training program of 2-4 exercises, 3 days per week, to complement their current endurance training programs.  

Improving Running Economy to Improve Performance

In the sport of running performance is easily quantified as the fastest time over a given distance.  The runners with the fastest times often have the best ability to utilize oxygen (VO2 max), process metabolites and substances involved in energy utilization (lactate threshold), and the most efficient running form.  Efficiency in running is described as running economy, similar to miles per gallon in a car, how much energy is expended to run a given distance and speed.  Interestingly, prior research has shown running economy is more predictive of running performance than VO2 max levels (Morgan et al. 1989).  As with many physiological variables there is significant variability in economy between runners with similar VO2 max levels.  Thus two runners can complete a run of the same distance in the same time, but expend different levels of energy.  Imagine an amateur athlete completing a training run with a professional runner.  The professional runner will be at a significantly lower intensity than the amateur. 

Among most runners an increase of 5-20% in VO2 max is observed with aerobic training, but genetics also limit the maximum level of oxygen utilization during activity.  Thus runners trying to improve their running performance should also consider beneficial changes in running economy.   Factors influencing running economy can be broken down into two categories, intrinsic factors inherent to the athlete and extrinsic factors such as running surface and shoe wear.  A recent review article in the journal Sports Medicine highlighted the evidence behind improving running economy (Moore et al. 2016).

A runner’s optimal stride length is mostly self determined by the athlete and represents a self-selected economical running form.  In trained runners stride length is on average 3% greater than optimal, but this percentage can be up to 8% in a novice runner (Ferrauti et al. 2010).   Making small changes in stride length can often improve running economy especially in the novice runner. 

Another variable highlighted in the article involved improving running biomechanics to improve running economy.  Energy wasted in the vertical and rotational planes by the upper or lower body are detrimental to increasing horizontal plane speed and efficiency.  For example, the amount of vertical or rotational displacement observed in the running cycle has been shown to adversely effect economy.  Surprisingly, time in contact with the ground has been an inconclusive variable to improve economy.  Faster stride frequency may reduce injury risk or pain with running, but also impacts energy required during running.  A tradeoff is observed between high stride frequency leading to increasing deceleration muscle costs vs. a lower stride frequency leading to increased energy absorption and potential injury risk.   Despite a commonly reported statement by tribes of runners there is inconclusive evidence that forefoot vs. rearfoot running is more economical. 

A final variable to consider would be the range of motion and muscular effort observed at the lower extremity joints between landing and push off.  An athlete will burn more energy per step if their hip, knee, and ankle move through greater ranges of motion compared to a more efficient runner.  Thus minimizing unnecessary movements will improve running economy and performance.

boulder running form retraining performance

The pros and cons of these variables on a runner's gait must be considered before making any changes.  Thus, runners interested in reducing injury risk and improving performance should utilize gait analysis by a Physical Therapist to evaluate their running gait and determine the most appropriate modifiable factors

 

 

 

Aging, The Older Athlete, and Running Speed
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Running is one of the most common forms of exercise due to its' wide appeal, minimal equipment needs, and aerobic benefits.  Around Boulder it is not uncommon to see runners of all ability levels and ages enjoying many of the great outdoor running paths and trails.  Prior research has shown older runners run at slower speeds than younger adults due to cardiovascular and musculoskeletal changes due to aging.  Exercise physiology research shows a 10% decline in cardiovascular capacity with each decade after age 40.  Thus a runner holding the same minute/mile pace would be running at a higher % of their VO2 max with each decade after 40.  

aerobic capacity over lifespan, runners

An interesting article by DeVita and colleagues examined the impact of aging on running biomechanics (Med Sci Sports Exerc 2015).  The authors examined 110 health runners within a biomechanics laboratory to determine running speed, running forces, and biomechanics.  The results showed running speed decreased in older runners secondary to a decrease in stride length but no change in stride rate (Running Speed = stride length x stride frequency).  This loss of stride length was accompanied by a stride height and push off due to decreased activation of the ankle musculature.  Interestingly, no change was noted in the hip and knee activation in these runners.  The loss of ankle strength may place these athletes at greater risk of ankle and foot injuries during run training.  It is not known if ankle strengthening could improve mechanics in these runners.  

Running Economy and Static Stretching
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Why to perform static stretching AFTER running:

The ability of an individual to reach maximal performance in distance running is determined by VO2 Max (the body’s ability to utilize oxygen), lactate threshold, and running economy. Running economy is determined by the oxygen cost to perform a given aerobic activity a sub maximum level. Similar to miles per gallon in a car, an athlete with a better running economy can sustain a given intensity and distance while preserving glycogen compared to a less economical runner. Prior research has indicated static stretching prior to a run will reduce running performance and should be replaced by more of a dynamic running warm up. In comparison, static stretching performed 2-3 days per week, 2-3 repetitions held for 15-60 seconds per stretch for muscles of the lower extremity after running. In practice we see a lack of hip flexor, quadriceps (rectus femoris), and calf flexibility to be some of the leading causes of mobility loss in a runner. This improvement in running mechanics will improve running economy in a runner leading to decreased injury risk and improved running performance. To learn more about the evaluation and treatment of running economy contact the experts at mendcolorado.com.