Running Economy

by Patti and Warren Finke, Team Oregon
The exercising body is only about 20 - 25% efficient meaning that about 75 - 80% of the energy generated during exercise is given off as heat. Differences in efficiency of runners of the same work capacity (VO2 Max) have been shown to yield variations in race times up to 20%!

It has been suggested that marathoners are more efficient than middle distance runners. This may be because marathon training induces greater changes in efficiency than training for shorter distances. It may be because more efficient runners tend to be more successful in marathons.

There are many components that contribute to running efficiency, some of which we can change and some we cannot. The interactions between the variables are complex and difficult to interpret. It is clear though that efficiency is an important element of performance.

Economy vs. Efficiency

According to the exercise physiologists, the word efficiency is defined by the work done related to the energy expended. They do not like to use efficiency when talking about running velocity or speed because speed is not directly a measure or work or energy. They prefer to use the word economy when talking about running speed and can physiologically define and measure that as the submaximal oxygen uptake per unit of body weight (i.e. The less oxygen needed per weight at a certain pace, the less energy used and the more economical the runner). We are going to take a more simplistic view since, as runners, most of us are interested mainly in how fast we can run a certain distance and how we can train to get faster. We will use efficiency in our discussion as we will be arbitrarily defining running power as how fast we can run a given distance or work per unit time. If we can become more efficient, the amount of running power available to us increases and we can run faster.

Although it is clear that efficiency is an important factor in performance it is not well understood. A review of the current literature raises more questions than it answers. Very few studies have been done pertaining to training efficiency and those conducted were relegated to anecdotal evidence since they tend to use few subjects or often only one.

EFFICIENCY FACTORS

Some of the contributing factors to running efficiency are:

Energy Optimization

The ability to use the correct energy conversion system to supply the most energy possible.

Biomechanical Considerations

Body mass and structure, dynamics, and shoes.

Neuromuscular Facilitation

Coordination and skill.

Other Physiologic and Environmental Factors

Gender, age, temperature, loss of fluids, and fatigue.

Psychological Factors

BIOMECHANICAL CONSIDERATIONS

Body Mass and Structure

Because the definition of economy is expressed as energy used per body weight, it is generally assumed that economy is independent of weight and that weight does not account for differences in efficiency between individuals. Some researchers measured no differences in efficiency in treadmill walking among lean, obese and weight added subjects. Others have found that heavier than average runners showed more efficiency than lighter ones. While data showed that adding some weight to the body may increase the energy needed, one researcher showed that adding up to 15% extra weight did not make any difference.

Body differences rather than running mechanics correlate with efficiency. This is especially true for those body elements reflecting linear dimension of the body( e.g., leg length, pelvic width, foot length). Many researchers felt that a runner with smaller mass in the extremities worked less to move that body than one with heavy limbs.

We noted in our earlier articles that many faster runners were fine boned and tended to be lean. This observation correlates well with the studies of efficiency. However, most of us learned long ago not to judge our competition on how they looked. We cannot change our basic body types, so what can we do to improve how mass affects our efficiency. Experience has shown us that overweight runners certainly improve their times as they lose weight, but being too lean can also cause problems. The key is to find the weight at which you perform well and stay healthy. Long experience has shown us that, over time, an adequately fueled exercising body tends to pick a healthy weight and body composition on its own.

Running Dynamics

Many researchers have shown that stride length directly affects efficiency. Individuals, however, subconsciously pick a stride length at a given speed that is most efficient for the individual's body. Experiments where the stride length and frequency were artificially changed, show a decrease in efficiency at all speeds. One interesting study of elite versus good marathoners showed that the stride length was less for the elite runners. Another showed that a group of distance runners, during their four year collegiate careers, shortened their strides at a given speed over 7 cm. The shortening or lengthening of the stride has an important effect on all of the active muscles, making the muscles work differently and changing efficiency. Correlations between leg length and stride length have not held up making it impossible to predict optimal stride length from leg length. Neither stride length nor leg length have been shown to correlate with energy expenditure. The major implications of all the research done are that well- trained runners tend to run with a stride length and a stride frequency extremely close to their optimal. The question asked is how do they pick both stride length and frequency? One theory is that they gravitate to the optimal based on feedback of perceived exertion by unconscious experimentation during training. Another possibility is simple physiological adaptation through repeated training at a particular combination of stride length and frequency for a given running speed. In any case, the research has shown that "form" coaching for long distance runners may be suspect. Good form for one runner may be poor form for another.

Shoes

Weight becomes more of an efficiency factor when it is added to the extremities, (i.e., the shoes). The addition of 100 grams of weight increases the energy cost by about 1% at moderate speeds. Another study with similar results also showed that added weight had less effect at faster speeds. An additional study found a 2.8% energy saving when using a well cushioned shoe rather than a poorly cushioned one of the same weight. Implications of these findings are in the areas of orthotic devices, light weight trainers and racing flats. The principle of risk vs. gain is important when evaluating these areas. We know many who take out their orthotics when they race; Maybe the weight makes less difference when we are running faster so leaving them in would be better. Running a couple of short races without the devices may not be much risk, but if you are racing frequently or running long distance events the risk of injury may be greater than the small gain in efficiency. Light weight trainers tend to wear out more rapidly and are not known for great support so your biomechanical and financial needs should be investigated before they are chosen. Racing flats give little or no support and tend to lack cushioning. Always the gains from less weight must be weighed against the increased risk of injury.

NEUROMUSCULAR FACILITATION

Muscles move in groups rather than individually. Some muscles must be contracted (agonistic) and coordinated with each other to produce the maximum contractile force. The antagonist muscles must relax in coordination with the contraction so that they don't provide unwanted resistance to the movement. Other muscles in the body also must coordinate in both contraction and relaxation to stabilize the body and maintain other body actions. During endurance activities, in each muscle, groups of muscle fibers are used to perform work while others are rested and vice versa. These complex processes are governed by neuromuscular coordination.

Neuromuscular coordination causes each movement to occur in the correct sequence and timing with just the right amount of force. Skilled performance occurs when the nerve impulses reach the proper muscle at the correct time to create the movement pattern. One of the important aspects of neuromuscular facilitation is the concept of reciprocal inhibition which means that when nerve impulses are sent to the muscles to contract, inhibitory impulses are carried to the antagonistic muscles to relax so that they do not interfere with the speed and forces of the desired movement. Controlled movements with less than maximum force and speed need some voluntary resistance. One of the determiners of skill has been shown to be excessive contraction by those antagonistic muscles. Repeated practice of the specific action establishes a conditioned reflex which is quickly recalled and integrated into the practiced activity. The more skilled we are at specific running movements, the less energy we will expend.

PHYSIOLOGIC AND ENVIRONMENTAL FACTORS

Gender

If we express economy in terms relative to body mass, the studies have shown little significant difference between men and women runners. Because women have more essential body fat and are smaller, some researchers have felt that women may need to expend more energy in longer distance events making them at a distinct disadvantage; other researchers have measured no differences.

Age

Studies comparing children, adolescents and adults definitely show that children require more energy to run at any given speed than adults. Quantitative studies show that the energy cost decreases about 2% per year from ages eight to eighteen. The factors mostly have to do with the natural body differences between growing children and adults. A few studies have shown that older adults are less efficient than younger ones, perhaps due to decreased flexibility, increased body fat and increased cardiac and respiratory demands. Maybe they take shorter strides to economize on the force production that an aging musculoskeletal system must generate and endure. While we have no way of measuring the energy cost of running in our training on a daily basis, our practical experience has shown us that older runners may need more recovery days than younger ones. This fact may lead us to agree that it may cost us more energy to run as we get older. Personally, as we have advanced in our Masters running careers, we have noticed that we can't train quite as strenuously as we could even three or four years ago. The runners we have coached in their 50's and older have noticed definite differences and require more rest days during the week or sometimes need to alternate hard/easy weeks.

Temperature and dehydration

As the temperature rises, it becomes harder and harder to run at the same pace. The effect of increased core temperature on performance is known to all of us who have raced on hot days. We lose efficiency in the heat because of the increased energy needed for other work besides speed; such as peripheral circulation, sweat gland activity and hyperventilation coupled with decreased energy metabolism efficiency. The main way that the body loses heat is through sweating and the evaporation of that sweat. That means that dehydration also plays a part in loss of performance in the heat. The core temperature rises 0.3 -0.5 degrees for every 1% loss of body weight accompanied by an increase in heart rate of six beats per minute. The body's response is mainly due to the loss of blood volume reducing the ability to transport heat from the core to the periphery and decreasing the blood, nutrients and oxygen to the working muscles. (See our previous Team Oregon Tip on running in the heat for details on heat adaptation and hazards.)

PSYCHOLOGICAL FACTORS

While differences in emotional state have not been shown to correlate with differences in efficiency between runners of the same ability, they may affect individual runners. Some performance variables and efficiency may be associated with natural fluctuations in mood states. We have all had good and bad runs because of our emotional state. Remember that "Life Stress is Total". Running injuries and poor running performance have correlated with stressful situations unrelated to running for us personally and for runners we've coached. Can we change our moods to help us run better? Perhaps, but it may be smarter to be cautious and train a little less when we're under severe stress and not expect great race performances during those times.

TRAINING

Training has been shown to improve efficiency. The greatest gains in efficiency are made by beginning runners, although experienced runners may gain a valuable edge over their competition by making even small efficiency improvements. What changes can training make and how can we train to make some desired gains in efficiency? The key word in training efficiency is SPECIFICITY.

For all the physiological efficiency factors, the goal is to develop optimal race performance patterns. Practice makes perfect. The more we practice and the more specific it is to the race, the better.

Beginning runners

More running will improve their running efficiency tremendously. The body weight will adjust to the demands of the exercise. Stride length and frequency will adjust to a more efficient pattern. Coordination of neuromuscular interaction will improve. The body will improve its ability to cool itself.

Experienced runners

Just training alone yields small if any changes for the experienced runners. Some changes in efficiency have been found training runners at anaerobic threshold when the test was performed at anaerobic threshold. The implications and conclusions of this research are that some training ought to be done at the pace or paces where we want to race to obtain efficiency at race pace. The concept of neuromuscular facilitation is probably the important one in training at a specific pace. The type of training that we suggest for specific race efficiency is the "tempo run". A "tempo run" of one fourth to one third of race distance at race pace can provide many physical and psychological benefits. The stride length and frequency for the pace can be optimized along with the coordination necessary to sustain the pace. The body and the mind learn what race pace feels like and can deal with the sensations of a race. All these things will improve efficiency under race conditions and ultimately performance.


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