High-energy phosphate metabolism during two bouts of progressive calf exercise in humans measured by phosphorus-31 magnetic resonance spectroscopy

Abstract

According to the literature the steady-state level of phosphocreatine (PCr) has a linear relationship to the workload during muscle exercise intensities below the lactate threshold, whereas this linearity is impaired during exercise intensities above the lactate threshold. The purpose of this study was to investigate the linearity between PCr kinetics and workload during two bouts of isotonic incremental calf exercise with transitions from moderate- to high-intensity as well as from high- to moderate-intensity work rates. Using a whole-body 1.5 T MR scanner and a self-built exercise bench, we performed serial phosphorus-31 magnetic resonance spectroscopy ((31)P-MRS) with a time resolution of 30 s in nine healthy male volunteers. Changes in PCr, inorganic phosphate (Pi) and pH were statistically evaluated in comparison to the baseline. The exercise protocol started with a 4.5 W interval of 6 min followed by two bouts of 1.5 W increments. The workload was increased in 2-min intervals up to 9 W during the first bout and up to 7.5 W during the second bout. The second bout was preceded by a 4.5 W interval of 2 min and followed by a 4.5 W interval of 4 min. PCr hydrolysis achieved a steady state during each increment and was highly linear to the work rate (r (2), -0.796; P <0.001). Pi accumulated during each bout, whereas the pH decreased continuously during the first bout and did not exhibit any substantial decrease during the second bout. The metabolite levels and pH were expressed as the median value and the range. Our study confirms that steady-state PCr levels also have a linear relationship to work intensities above the lactate threshold, while pH changes do not have any impact on PCr degradation. The lack of substantial changes in pH during the second exercise bout indicates that prior high-intensity exercise leads to an activation of oxidative phosphorylation.

High-energy phosphate metabolism in the calf muscle of healthy humans during incremental calf exercise with and without moderate cuff stenosis

“…Consequently, PCr, serving as a reserve and a shuttle for HEP from the mitochondrial to the myofibril site, decreases progressively, until the blood flow and the O 2 supply are adapted and PCr hydrolysis passes into a steady state (Grassi 2005). The extent of PCr decreases until steady-state is linearly related to the workload and reflects the main part of the O 2 deficit (Di Prampero 1981;Di Prampero et al 2003;Schocke et al 2004aSchocke et al , 2005. The PCr changes between two steady-states follow a mono-exponential order, characterized by a time constant, which ranges between about 20 and 45 s in healthy humans (Binzoni 2003;McCreary et al 1996;Simond et al 2001).…”

“…The significant correlation between the PCr time constants and the pH values at the end of increments as well as the significant correlation between the PCr recovery rate and the pH at the end of exercise, as already detected by several previous 31P MRS studies (Hug et al 2005;Iotti et al 2004), might also reflect this biochemical interrelation between ATP hydrolysis and PCr metabolism. This biochemical interrelation might be emphasized in the skeletal muscle because of the extensive shifts of metabolites during contraction of the fast-twitch fibres, which are related to the workload (Robergs et al 2004;Saks et al 2004;Schocke et al 2005).…”

“…The same investigator did the segmentation of the images in order to eliminate interobserver bias. The total mass of each triceps surae was calculated assuming a muscular density of 1.056 g/ ml Schocke et al 2005) and used for correction of the mechanical power according to a recent study showing that VO2Peak is closely related to the amount of exercising muscle mass (Sanada et al 2005). …”

Phosphocreatine Kinetics in the Calf Muscle of Patients with Bilateral Symptomatic Peripheral Arterial Disease during Exhaustive Incremental Exercise

“…Both parameters reflect the amount of ATP hydrolyzed during muscle contraction and the mismatch of mitochondrial ATP production, which accumulates with increasing impairment of oxygen supply [4,5,13,35]. PCr serves as a Bshuttle^for high-energy phosphates from the mitochondria to the myofibrils, whereby the extent of PCr hydrolysis depends on oxygen uptake, mitochondrial density and function, and work intensity [12,36,37]. Moreover, PCr represents the major part of the cumulative oxygen deficit within the muscle [38].…”

High-Energy Phosphate Metabolism During Calf Ergometry in Patients With Isolated Aorto-Iliac Artery Stenoses

“…25,26 The pedal ergometer consisted of one pedal that was conjoint to a piston and a cylinder and mounted on the middle of a wooden bench. The cylinder was connected to an air pressure system for the exercise protocol.…”