Muscle fatigue resistance during stimulated contractions is reduced in young male smokers.

Aim: To determine whether muscle function is compromised in healthy smokers in comparison with activity-matched non-smokers. Methods: Nine male smokers (aged 22.2 ± 2.5 years: mean ± SD) with a smoking history of 2.5 ± 3.1 pack years, and ten male control participants (25.4 ± 2.9 years) matched for physical activity level participated in this study. Knee extensor strength was measured using isometric maximal voluntary contractions. Voluntary activation of the quadriceps and co-activation of the biceps femoris were determined using interpolated twitches and surface electromyography respectively. The frequency-torque relationship and fatigue resistance were assessed with electrically evoked contractions. A fatigue index was determined as the ratio of final torque to initial torque during a series of isometric contractions (2 min; 30 Hz; 1 s contraction/1 s rest). Quadriceps anatomical cross sectional area was measured with MRI at 50% of femur length. Results: Maximal voluntary contraction torque, quadriceps anatomical cross sectional area, knee extensor torque/quadriceps cross sectional area, activation, co-activation and force-frequency relationship were similar, whereas the fatigue index was 17% lower in smokers than non-smokers. Conclusion: In young men smoking does not significantly affect quadriceps muscle mass and contractile properties, but does reduce fatigue resistance of the quadriceps muscle, which was not attributable to differences in physical activity. © 2007 The Authors

Fruit-bearing branchlets are carbon autonomous in mature broad-leaved temperate forest trees

In order to evaluate the degree of carbon autonomy for fruit development, the carbon source-sink relationship in fruit-bearing branchlets of mature deciduous forest trees was manipulated in situ. The tests included half and complete defoliation, girdling or the combination of both treatments, which were applied on fruiting branchlets by using a canopy crane. Concentrations of non-structural carbohydrates (NSC) were analysed in different branchlet tissues and fruits, to identify situations of carbon imbalances induced by the treatments. NSC concentrations of branchlets were generally lower under treatments resulting in decreased fruit growth. All three investigated species (Carpinus betulus, Fagus sylvatica and Tilia platyphyllos) exhibited complete carbon autonomy of fruiting at the level of whole, undisturbed branchlets, since neither a decrease of total infructescence biomass, nor of individual fruit mass occurred on girdled, un-defoliated branchlets. On girdled, 100% defoliated branchlets, fruit biomass relative to controls decreased by approximately 50% in Carpinus and Tilia, but by almost 80% in Fagus, which can be explained by different proportions of photosynthetically active infructescence tissues among the species. In contrast to the other two species, Tilia branchlets did not import carbon to compensate for assimilate loss after defoliation