"Maailman parhaat urheilijat pärjäävät, koska he tekevät runsaasti lyhyitä, toistuvia, rankkoja harjoitteita", professori George Brooks Kalifornian Yliopistosta sanoo. Tällainen intervalliharjoitus synnyttää paljon laktaattia, mihin keho puolestaan sopeutuu vahvistamalla lihassolujen mitokondrioita: ne polttavat laktaatin energiaksi. Näyttää siltä, että hapellinen (aerobinen) ja hapeton aineenvaihdunta kietoutuvat laktaatin välityksellä toisiinsa.
Heikkokuntoisemmissa näin ei kuitenkaan käy, vaan maitohappo kertyy kivuliaasti lihakseen. "Valmentajat ja urheilijat eivät välttämättä usko tätä, mutta kestävyysharjoittelu opettaa kehon käyttämään myös maitohappoa energialähteenään", sanoo professori Brooks.
Tutkimus on julkaistu American Journal of Physiology Endocrinology and Metabolism -julkaisussa.
Lisätietoa University of California at Berkeleyn tiedotteessa.
Training helps people get rid of the lactic acid before it can build to the point where it causes muscle fatigue, and at the cellular level, Brooks said, training means growing the mitochondria in muscle cells. The mitochondria - often called the powerhouse of the cell - is where lactate is burned for energy.
"The world's best athletes stay competitive by interval training," Brooks said, referring to repeated short, but intense, bouts of exercise. "The intense exercise generates big lactate loads, and the body adapts by building up mitochondria to clear lactic acid quickly. If you use it up, it doesn't accumulate."
To move, muscles need energy in the form of ATP, adenosine triphosphate. Most people think glucose, a sugar, supplies this energy, but during intense exercise, it's too little and too slow as an energy source, forcing muscles to rely on glycogen, a carbohydrate stored inside muscle cells. For both fuels, the basic chemical reactions producing ATP and generating lactate comprise the glycolytic pathway, often called anaerobic metabolism because no oxygen is needed. This pathway was thought to be separate from the oxygen-based oxidative pathway, sometimes called aerobic metabolism, used to burn lactate and other fuels in the body's tissues.
"This experiment is the clincher, proving that lactate is the link between glycolytic metabolism, which breaks down carbohydrates, and oxidative metabolism, which uses oxygen to break down various fuels," Brooks said.
Post-doctoral researcher Takeshi Hashimoto and staff research associate Rajaa Hussien established this by labeling and showing colocalization of three critical pieces of the lactate pathway: the lactate transporter protein; the enzyme lactate dehydrogenase, which catalyzes the first step in the conversion of lactate into energy; and mitochondrial cytochrome oxidase, the protein complex where oxygen is used. Peering at skeletal muscle cells through a confocal microscope, the two scientists saw these proteins sitting together inside the mitochondria, attached to the mitochondrial membrane, proving that the "intracellular lactate shuttle" is directly connected to the enzymes in the mitochondria that burn lactate with oxygen.
"Our findings can help athletes and trainers design training regimens and also avoid overtraining, which can kill muscle cells," Brooks said. "Athletes may instinctively train in a way that builds up mitochondria, but if you never know the mechanism, you never know whether what you do is the right thing. These discoveries reshape fundamental thinking on the organization, function and regulation of major pathways of metabolism."
Lähde: Tiede-lehti, 29.4.2006
