ptonthenet Energy Expenditure for Running by Rob Orr This article examines various training methods available for running and the impact of those methods upon energy expenditure. Energy Expenditure Energy expenditure is of primary importance to all runners. The more economical the technique, the more energy saved at a given intensity. This allows either an increase in workload or an energy saving. This would mean that differences in efficiency greatly effect the training effort. Mechanical running efficiency can differ up to 50 percent, even among skilled runners. As McArdle, Katch & Katch et al. state "...distance athletes as a group tend to run with between five to 10 percent more economy than well-trained middle-distance runners." Running vs Walking There is a certain speed at which running becomes more economical than walking, this speed is said to be around 8.0 to 9.0 km/hr. The importance of this is clear for those athletes who participate in events that require an extended distance to be covered, eg. military pack marching, rogaining or long distance hiking, who believe that by walking fast instead of running they conserve more energy. As McArdle, Katch & Katch state "…the economy of walking faster than 8 km per hour was one-half of that for running at similar speeds." Shoe Weight Even the weight of footwear effects energy expenditure. For every additional 100g of weight worn (per shoe) during moderate running, oxygen uptake is increased by one percent. However, not only does the weight of the foot wear effect energy expenditure but so to does the cushioning. As McArdle, Katch & Katch state "...shoes with different cushioning properties also effect the economy of movement with a softer-soled running shoe reducing oxygen cost of running at a moderate speed by about 2.4 percent compared to a similar shoe with a firmer cushioning system." Interestingly, this was found with the softer-soled shoe being 31 grams heavier. Air and Hills Air resistance plays a large part in energy expenditure. Depending on speed, overcoming air resistance on a calm day can account for three to nine percent of the total energy. It is commonly thought that the additional energy utilised running against the wind is saved on the return trip, with the wind at the back. However, this is not the case, the gain over the return trip is not as large as the loss. The same applies for running hills; more energy is utilized running up hill than is "caught up" running back down. Weights Hand held weights do increase the metabolic cost of walking; however, there is also an increase in systolic blood pressure (which may be due to the "gripping" of the hand weights.). They may therefore be contra-indicated for athletes suffering from hypertension. When considering running with hand weights, the increase in metabolic expenditure would be better acquired through increases in pace or distance, as the higher impact of running, combined with the increase in load, has the potential to lead to impact orientated injuries. Training Methods Speed assisted training Speed assisted training is commonly used by athletes to "pattern" their legs to higher stride frequencies. There are many methods of performing speed assisted training, from pre-stretched bungie cord to being pulled behind a bike or car. The most common method is down hill running. However, be aware that a decline greater than -2 is said to alter technique in a non productive fashion. Therefore, "the maximal downhill slope that can be used to increase running speeds is -2." Suspended Deep Water Running SDWR is a training technique becoming more increasingly popular. It was designed in an attempt to produce similar cardio vascular conditioning for runners without the continuous impact of hard surface running (HSR). Due to the effect of water (as discussed in previous article), studies found that both max HR and max VO2 are lower. It should be noted that the rate of perceived exertion (RPE) for a set intensity was also lower in the SDWR than conventional HSR. Participants thought they where working harder than they actually were. This could be caused by the increased resistance of the water, which results in greater lactate production. Becky et al suggested that "individuals using RPE to regulate their training intensities during SDWR should work at higher RPE levels than those on land." Treadmill vs Hard Surface Running As many of the regular users may already feel there is a big difference between running/walking on a treadmill and on the ground. As the tread rolls backward it drags the foot backwards eliminating the need for the hamstrings and gluteals to pull the upper body forward thus making the movement easier. However the hip flexors now have to work harder to move the foot being dragged backward, forward. The machine also sets the pace, which may be useful in establishing the movement patterns and timing (rhythm) for a faster land pace. However, do not forget that when running on land, athletes may tend to slow down due to terrain, fatigue and other factors. A machine that maintains a set speed requirement does not necessarily improve the athletes’ mental concentration to maintain a pace. Another considerable factor is the fact that skeletal impact is considerably less on the stride machine as there is a flexible-striding surface located underneath most stride belts. This cushions the impact, making it a valuable rehabilitation aid. With all this in mind, there may be little difference in energy expenditure between track and treadmill running. As McArdle, Katch & Katch state while referring to a study of eight distance runners conducting a protocol of treadmill and track running, "There was no measurable differences in the aerobic requirements of submaximal running (up to 286 m per min) on the treadmill or track (either on level or up a grade) or between the maximal oxygen consumption measured in both forms of exercise under similar environmental conditions."
Posted on: Thu, 08 Aug 2013 03:26:17 +0000