forbrænding - hvad giver mest?

[Jan D.]

Jeg er ikke sikker på der er den store uenighed og prøver derfor lige kort at skitsere 3 hovedkonklusioner:

- tommelfingerreglen 1 kcal pr. km pr. kg er et nogenlunde rigtigt udgangspunkt for løb uanset tempoet

- at gang i mere moderat tempo ikke er så energikrævende som løb (men der måske ikke er alverden til forskel pr. km)

- højintensiv træning er konditionsmæssigt bedre end lavintensiv træning (uanset forbehold)

Det vi diskuterer nu er så om højere løbetempo forbrænder flere kcal pr. km. Her viser standardformlen ingen forskel. Jeg vil også umiddelbart tro at en højere intensitet medfører højere forbrænding pr. km, men jeg kender ikke nogen videnskabelig reference til at dokumentere dette.

Spørgsmål er også om det har nogen nævneværdig betydning. Her tror jeg det er relativt få procent, der er tale om. Hvis man ønsker at tæller forbrændingskalorier er der i forvejen et hav af usikkerhedsmomenter, der vil gøre en opgørelse upræcis. Det vil alene kunne anvendes som en niveaumæssig retningssnor.

Nej, sikkert ikke. Men kan du så ikke opremse årsagerne for os som ikke helt er med på hvad trætheden skyldes helt præcist? Og når du har nævnt årsagerne til trætheden, er der så ikke mulighed for at disse årsager er energikrævende?

Dette ville føre for vidt ind i fysiologiens verden. Jeg mener det er selvindlysende at fx kipketer vil være mere træt efter en 800 m - konkurrence end at løbe fx 2.000 m i lunte tempo. Det er velkendt for enhver erfaren motionist, at det i lige så høj grad er intensiteten som mængden, der trætter og stiller krav om restitution.

Edited September 1, 2004 by Jan D.

[Sputnik]

Eur J Appl Physiol. 2003 Jan;88(4-5):297-316. Epub 2002 Nov 13. Related Articles, Links 

 

Biomechanical and physiological aspects of legged locomotion in humans.

Saibene F, Minetti AE.

Istituto Neuroscienze e Bioimmagini, Consiglio Nazionale delle Ricerche, Via Fratelli Cervi 93, 20090 Segrate, Milan, Italy. [email protected]

Walking and running, the two basic gaits used by man, are very complex movements. They can, however, be described using two simple models: an inverted pendulum and a spring. Muscles must contract at each step to move the body segments in the proper sequence but the work done is, in part, relieved by the interplay of mechanical energies, potential and kinetic in walking, and elastic in running. This explains why there is an optimal speed of walking (minimal metabolic cost of about 2 J.kg(-1).m(-1) at about 1.11 m.s(-1)) and why the cost of running is constant and independent of speed (about 4 J.kg(-1).m(-1)). Historically, the mechanical work of locomotion has been divided into external and internal work. The former is the work done to raise and accelerate the body centre of mass (m) within the environment, the latter is the work done to accelerate the body segments with respect to the centre of m. The total work has been calculated, somewhat arbitrarily, as the sum of the two. While the changes of potential and kinetic energies can be accurately measured, the contribution of the elastic energy cannot easily be assessed, nor can the true work performed by the muscles. Many factors can affect the work of locomotion--the gradient of the terrain, body size (height and body m), and gravity. The partitioning of positive and negative work and their different efficiencies explain why the most economical gradient is about -10% (1.1 J.kg(-1).m(-1) at 1.3 m.s(-1) for walking, and 3.1 J.kg(-1).m(-1) at between 3 and 4 m.s(-1) for running). The mechanics of walking of children, pigmies and dwarfs, in particular the recovery of energy at each step, is not different from that of taller (normal sized) individuals when the speed is expressed in dynamically equivalent terms (Froude number). An extra load, external or internal (obesity) affects internal and external work according to the distribution of the added m. Different gravitational environments determine the optimal speed of walking and the speed of transition from walking to running: at more than 1 g it is easier to walk than to run, and it is the opposite at less than 1 g. Passive aids, such as skis or skates, allow an increase in the speed of progression, but the mechanics of the locomotion cannot be simply described using the models for walking and running because step frequency, the proportion of step duration during which the foot is in contact with the ground, the position of the limbs, the force exerted on the ground and the time of its application are all different.

Min fremhævning i artiklen.

Gang bruger ved den energioptimale hastighed (1,11 m/s eller ca. 4 km/t) 2 kJ pr. km pr. kg, mens løb bruger 4 kJ pr. km pr. kg uafhængigt af hastigheden. Dvs. at man forbrænder ca. dobbelt så meget energi ved at løbe en given distance, i forhold til at gå den.