It is true that the result, W (as in W-orlkload) = F (as in F-orce) x d (as in d-istance) will "look" like it should tell you the amount of Energy that's been necessary to move the object from A to B, but that would require that (a) all the bio-chemical energy your body produces would be converted to mechanical energy and none would be lost and (b) the acceleration and thus force (F = mass x acceleration) would be constant - both pretty irrational assumption even for a non-physicist, I should say.
Against that background it should not surprise you that a recent study from the School of Sports and Exercise Sciences at the University of Rome does now report:
3.5x higher energy expenditure / m on short (10m) vs. long (20m) shuttle runs
Kinetic measurement / estimation of the energy expenditure - how did that work? (1) The velocity profile during the shuttle runs was determined by means of a high-frequency camera. (2) The video was then analyzed using free software Kinovea-0.8.7 to obtain the actual distance covered by the center of mass of the subject over each nominal 2-m stretch as well as the corresponding time. (3) This allowed for the calculation of the time course of the speed [note to this ends they did not use the time-integral over M x v²/2, which would be how it's done, but simply the peak v-elocity], and, hence, of the corresponding acceleration, as well as the peak speed, which where then used to "estimate" (Buglione. 2013) the energy cost of shuttle running by multiplying it with a variable ny (~0.25; cf. Prampero. 2005) describing the efficiency of mechanical work and adding the result to energy cost of constant speed running.To measure this difference, Buglione and di Prampero conducted two experiments. For experiment one, they invited
- 29 physically active subjects practicing in various amateur sporting activities,
- 28 professional soccer players and
- 8 high-level runners
measurements over 155 trials and
- 10 subjects of 25.4±3.9 age (years), 70.3±2.6 body mass (kg), 1.75±0.05 stature (m) belonging to the Italian national field hockey team
Kinetics + math = cheap but not always accurate
|Remember the last study involving a shuttle run? It dealt with the ergogenic effects of glycerol (read more).|
This observation confirms Antonio Buglione and Pietro Enrico di Prampero hypothesis that their "kinetic approach" would qualify to as a assess the energy expenditure during high intensity (intermittent) exercises like the shuttle run over long(er) distances without having to resort to expensive experimental equipment.
Remember: All it takes is a cheap Casio Exilim EX-FH25 to record the runs at a high-frequency of 210 Hz and the video software.
What's the physiological underpinning of the short vs. long difference?
Now, analyzing the underlying physiological mechanisms that yield the directly measured 3.5x increase in energy expenditure during the short 20m shuttle runs was not part of the Italians' study. Therefore we will have to invoke the results of another recently published study by Jared R. Fletcher et al. from the Human Performance Laboratory at the Faculty of Kinesiology of the University of Calgary (Fletcher. 2013), who set out to answer the question: "Can muscle shortening alone, explain the energy cost of muscle contraction in vivo?"
Their results, part of which you can see in figure 2 clearly indicate that the actual energy energy that's necessary to maintain a given torque (which is what you would usually calculate based on the weight and the lever, e.g. the poundage on the bar and the length of your forearm for a simplistic model of a biceps curl), increases almost linearly with the shortening velocity.
Moroever, kinetic (=moving the weight) vs. isokinetic (=static) exercises resulted in significantly greater muscle shortening and greater shortening velocity. I is therefore not surprising that the isokinetic plantarflexion contraction the 19 triathletes who were in the pre-competition phase of their training performed during the testing session (30 reps at 1/s) resulted in a +19% greater energy expenditure than their isometric counterpart.
The main finding in this study was that when greater MG fascicle shortening was imposed, the rate of muscle oxygen uptake increased.
Figure 2: The relationship between the rate of energy use to maintain a given torque and magnitude of muscle fascicle shortening (cm).
We assume this measured oxygen uptake is proportional to the total EC [energy consumption] of the muscle contractions; that is, any anaerobic energy utilization would increase in proportion with the increases in oxygen uptake. (Fletcher. 2013; my emphasis)
Bottom line: Overall, the two studies have a general, and two very practical take home messages. The general one is that you cannot calculate the amount of energy your body will consume during a certain exercise / movement paper based on simplistic equations that have been developed to be applied to standardized weights on straight levers that are moved with constant velocity along strictly linear or circular paths and against constant, at best linearly in-/decreasing resistances.
The practical take home messages, on the other hand, are that you (a) want to maximize muscular activity and that you (b) achieve that with short, intense, fast, yet not ballistic (no cheating the weight over 95% of the distance) kinetic movements. If you doubt the validity of this approach in terms of it's ability to help you shed body fat, you just have to take another look at one of the following posts:
Another suggested read: "Some HIIT For Life & Less LISS For More! How to Burn 27,300 Kcal Extra W/out Losing a Single Extra Pound of Fat!" A perfect example of the fallacy of simplistic energy expenditure calculations (read more)
- Eight HIIT Sessions on the Rowing Ergometer Cut Body Fat, Increase Adiponectin, VO2Max & Performance in National Level Rowers - Workmatched Classic "Cardio" Does Nothing (read more)
- Reduced Exertion High Intensity Training - A Minimalist 2x20s HIIT Protocol For The Male Convenience Generation (read more)
- The Iranian HIIT Solution: Three 200m Sprint Sessions per Week Double Insulin Sensitivity & Normalize Leptin Levels (read more)
- Buglione, A. di Prampero, PE. The energy cost of shuttle running. Eur J Appl Physiol. 2013 [epub ahead of print]
- di Prampero PE, Fusi S, Sepulcri L, Morin JB, Belli A, Antonutto G. Sprint running: a new energetic approach. J Exp Biol. 2005 Jul;208(Pt 14):2809-16.
- Fletcher JR, Groves EM, Pfister TR, MacIntosh, BR. Can muscle shortening alone, explain the energy cost of muscle contraction in vivo? Eur J Appl Physiol. 2013 [epub ahead of print]