european college of sport science

OP-BM01 Biomechanics 1
DO SKELETAL MUSCLE MITOCHONDRIA PLAY A ROLE IN THE REDUCTION OF VO2MAX WITH MODERATE HYPOXIA IN
ENDURANCE ATHLETES?
PONSOT, E., DUFOUR, S.P., DOUTRELEAU, S., LONSDORFER-WOLF, E., LAMPERT, E., PIQUARD, F., GENY, B., METTAUER, B.,
VENTURA-CLAPIER, R., RICHARD, R.
HÔPITAL CIVIL AND UNIVERSITÉ DE STRASBOURG
Introduction: Hypoxic environments have repeatedly been observed to depress VO2max during whole-body exercise in humans (Fulco et
al., 1998). The mechanisms behind the wide interindividual variability of the reduction of VO2max with hypoxia are largely unknown,
especially in a homogenous group of athletes (Lawler et al., 1988; Robergs et al., 1998). The present study investigates the role of cardiac
output (Q), arteriovenous oxygen difference (DavO2) and mitochondrial function in the limitation of VO2max with moderate hypoxia
(FIO2=14.5 %) in a homogenous group of endurance athletes.
Methods: 15 endurance trained athletes (normoxic VO2max =58.6±1.7 ml/min/kg) performed maximal cycle incremental tests to assess
VO2max, Qmax and DavO2max in normoxia and moderate hypoxia. Muscle biopsies of vastus lateralis were taken one week before the
cycling tests to evaluate the maximal muscle oxidative capacity (Vmax) and the sensitivity of mitochondrial respiration to ADP (Km) with
and without creatine (Cr) on permeabilized muscle fibers in situ.
Results: Athletes exhibiting the largest reduction of VO2max in moderate hypoxia (SL group: -18±2%) suffered from both significant reductions
in Qmax (-4±1%) and DavO2max (-14±2%). Athletes who tolerated well hypoxia, as attested by a significantly smaller drop of
VO2max with hypoxia (ML group: -7±1%), also displayed a blunted Qmax (-9±2%) but, conversely, were able to maintain DavO2max
(+1±2%;). Even though Vmax was similar in the two experimental groups, the smallest reduction of VO2max with moderate hypoxia was
observed in those athletes presenting the lowest apparent Km for ADP in presence of creatine (Km+Cr).
Conclusion
In already trained athletes with high muscular oxidative capacities, the qualitative rather than quantitative aspects of the mitochondrial
function may constitute a limiting factor to aerobic ATP turnover when exercising in lower oxygen availability, presumably through the
functional coupling between the mi-CK and ATP production. This study suggests a potential role for peripheral factors, including intrinsic
mitochondrial properties, in determining the tolerance to hypoxia in maximally exercising endurance-trained athletes.
References
Fulco CS, Rock PB & Cymerman A. (1998). Maximal and submaximal exercise performance at altitude. Aviat Space Environ Med 69, 793-
801.
Lawler J, Powers SK & Thompson D. (1988). Linear relationship between VO2max and VO2max decrement during exposure to acute
hypoxia. J Appl Physiol 64, 1486-1492.
Robergs RA, Quintana R, Parker DL & Frankel CC. (1998). Multiple variables explain the variability in the decrement in VO2max during
acute hypobaric hypoxia. Med Sci Sports Exerc 30, 869-879.
Authors’ Institutions:
- Ponsot E: School of Health and Medical Sciences, Örebro University, Sweden
- Mettauer B: Service de Cardiologie, Hôpitaux Civils de Colmar, France
- Ventura-Clapier R: U-769 INSERM, Faculté de Pharmacie, Châtenay-Malabry, France
10:15 - 11:45
Oral presentations
OP-BM01 Biomechanics 1
EFFECTS OF CONTRACTION ON PATELLAR TENDON MOMENT ARM AND FORCES DURING ISOMETRIC AND ISOKINETIC
KNEE EXTENSION
BALTZOPOULOS, V., TSAOPOULOS, D., RICHARDS, P.J., MAGANARIS, C.
MANCHESTER METROPOLITAN UNIVERSITY; *UNIVERSITY HOSPITAL OF NORTH STAFFORDHSIRE NHS TRUST
Accurate values of moment arms are of vital importance for accurate calculation of internal muscle-tendon and joint forces. During knee
joint extension, patellar tendon (PT) moment arm length (dPT) has been quantified from cadaveric data or in vivo imaging at rest. However,
moment arms change with muscle contraction (Tsaopoulos et al., 2007) and it is well recognized that moment arms at the time the
load is exerted are required for the realistic estimation of muscle and joint forces. The purpose of this study was to calculate the PT force
using contraction-specific moment arm measurements during isometric, isokinetic concentric and eccentric knee extensions.
Eleven healthy males (age: 25.3 years, height: 178.4 cm, body mass: 72.3 kg) volunteered for this study after signing informed consent
and radiation risk information forms. The maximum radiation exposure time was limited to 15 s for each person giving a maximum
effective radiation dose