Relationship between local perfusion and FFA uptake in human skeletal muscle—no effect of increased physical activity and aerobic fitness

Abstract

We investigated heredity-independent effects of increased physical activity and aerobic fitness on skeletal muscle free fatty acid (FFA) uptake, perfusion, and their heterogeneity at rest and during exercise. Also, the relationship between local skeletal muscle FFA uptake and perfusion was studied. Nine young adult male monozygotic twin pairs with significant difference in physical activity [229 min (SD 156) average time spent for conditioning exercise per week in more and 98 min (SD 71) in less active twins, P = 0.013] and aerobic fitness [18% (SD 10) difference in maximum O2 uptake] between brothers were studied using positron emission tomography. Submaximal knee-extension exercise increased perfusion, FFA uptake, and oxygen uptake in quadriceps femoris muscles 6-10 times compared with resting values (P < 0.001). More active twins tended to utilize more oxygen, while no differences were found in muscle perfusion or FFA uptake between groups. Mean perfusion and FFA uptake correlated strongly at a whole muscle level, both at rest (r = 0.97, P = 0.03 in more and r = 0.98, P = 0.02 in less active twins) and during exercise (r = 0.99, P = 0.01 and r = 0.94, P = 0.06), but at the voxel level (87 mm3) correlation was only moderate during exercise [r = 0.73 (SD 0.08) vs. r = 0.74 (SD 0.10), P = 0.92] and weak at rest [r = 0.28 (SD 0.13) vs. r = 0.33 (SD 0.21), P = 0.58]. Exercise decreased both perfusion and FFA uptake heterogeneity within the muscles (P < 0.001) similarly in both groups. In conclusion, long-term history of moderately increased physical activity tends to enhance muscle oxidative metabolism, but it does not have any significant influence on the FFA uptake or perfusion rates or their heterogeneity in skeletal muscle. Submaximal knee-extension exercise decreases heterogeneity of muscle FFA uptake and perfusion and improves matching between local muscle perfusion and FFA uptake. Thus it seems that the genetic influence is more important to determine the heterogeneity of perfusion and FFA uptake in skeletal muscle than exercise training.

Neuromuscular activation of vastus intermedius muscle during fatiguing exercise

“…Hannukainen et al (2006) demonstrated that perfusion and FFA uptake levels were higher in the VI muscle than in the other three synergists (Hannukainen et al, 2006). Since intracellular metabolism or membrane potential could be strongly related to blood flow behavior (Moritani et al, 1992;Sjøgaard et al, 1988), variance in surface EMG signal response during sustained contraction among the four muscles of the QF muscle group could be reflected in different blood flows among individual muscle components.…”

“…Neuromuscular activation of all four components of the QF muscle group has thus not been covered using surface EMG techniques in previous studies. However, the importance and specificity of the VI muscle in force generation during knee extension has been reported (Blazevich et al, 2006;Hannukainen et al, 2006;Lieb and Perry, 1968;Zhang et al, 2003). It was estimated that the contribution of the VI muscle was up to 50% of electrical stimulation-evoked knee extension torque during submaximal isometric contraction (Zhang et al, 2003).…”

“…It was estimated that the contribution of the VI muscle was up to 50% of electrical stimulation-evoked knee extension torque during submaximal isometric contraction (Zhang et al, 2003). Using positron emission tomography (PET), Hannukainen et al (2006) reported that muscle perfusion and free fatty acid (FFA) uptake levels, which might be dependent up on the degree of use among components of the QF muscle group were highest in the VI muscle (Hannukainen et al, 2006). To fully understand motor control of the QF muscle group, neuromuscular activation of all components of the muscle group including the VI muscle must be studied.…”

“…amplitude and frequency components, detected from the four components of the QF muscle group during isometric knee extension were compared to characterize fatigue-associated neuromuscular activation of the VI muscle. We hypothesized that the temporal changes in surface EMG variables of the VI muscle are inconsistent compared with other synergists of the QF muscle group during the fatiguing task since the previous studies using PET reported that the metabolism differs between the VI muscle and the other muscle components of the QF muscle group (Hannukainen et al, 2006).…”

Twin Studies in Finland 2006

“…All subjects completed a maximum oxygen uptake (VO2 max) test, electrocardiography and echocardiography studies. Positron Emission Tomography (PET) imaging studies of liver and muscle metabolism were conducted during an exercise protocol (Hannukainen et al, 2006).…”