Monica Zehnder

Muscle glycogen degradation during simulation of a fatiguing soccer match in elite soccer players examined noninvasively by 13C-MRS.

PURPOSE The purpose of this research project was to noninvasively determine individual muscle glycogen [Gly] degradation during a test intended to predict individual fatigue in intense soccer matches. METHODS The [Gly] of the calf muscles of 17 elite soccer players [age = 17.4 +/- 0.8 (SD)] were measured with 13C-MRS before and after an alternating velocity test to exhaustion. Blood samples were taken before and 3 min after the test for determination of blood metabolites. RESULTS Average muscle [Gly] was 135 +/- 53 mmol x (kg wet weight)(-1) before and 87 +/- 27 mmol x (kg wet weight)(-1) (P < 0.001) after exhaustion (42 +/- 25 min). There was a high correlation (r = 0.87, P < 0.0001) between muscle [Gly] at rest and net muscle [Gly] utilized. There was also a more moderate correlation (r = 0.62, P < 0.01) between net muscle [Gly] used and time to exhaustion during the soccer-specific test. There was some evidence of correlation (r = 0.42, P = 0.09) between resting [Gly] and time to exhaustion. Plasma lactate increased (P < 0.001) from 0.8 +/- 0.4 before the test to 2.5 +/- 1.0 mmol x L(-1) at exhaustion, whereas ammonia was raised (P < 0.0001) from 44.1 +/- 10.3 to 89.7 +/- 14.9 micromol x L(-1). Similarly, plasma free fatty acids were elevated (P < 0.0001) from 148 +/- 106 to 797 +/- 401 micromol x L(-1), and glycerol was increased (P < 0.0001) from 48.3 +/- 17.7 to 182.2 +/- 61.8 micromol x L(-1). Insulin levels (11.9 +/- 3.7 vs 11.7 +/- 4.8 microU x mL(-1)) remained the same. Creatine kinase levels increased (P < 0.0001) from 486 +/- 501 to 640 +/- 548 micromol x L(-1) after the test. CONCLUSIONS We conclude that exhaustion during soccer-specific performance is related to the capacity to utilize muscle [Gly]. The results underline the importance of dietary counseling (glycogen loading and resynthesis strategies) and proper training to enhance the glycogen levels and glycogenolytic capacity of the players.

Skeletal muscle 1H MRSI before and after prolonged exercise. I. muscle specific depletion of intramyocellular lipids

Aim of the study was to determine distribution and depletion patterns of intramyocellular lipids (IMCL) in leg muscles before and after two types of standardized endurance exercise. 1H‐magnetic resonance spectroscopic imaging was performed ( 1 ) in the thigh of eight‐trained cyclists after exercising on an ergometer for 3 h at 52 ± 8% of maximal speed and ( 2 ) in the lower leg of eight‐trained runners after exercising on a treadmill for 3 h at 49 ± 3% of maximal workload. Pre‐exercise IMCL contents were reduced postexercise in 11 out of 13 investigated upper and lower leg muscles (P < 0.015 for all). A strong linear correlation with a slope of ∼0.5 between pre‐exercise IMCL content and IMCL depletion was found. IMCL depletion differed strongly between muscles. Absolute and also relative IMCL reduction was significantly higher in muscles with predominantly slow fibers compared to those with fast fibers. Creatine levels and fiber orientation were stable and unchanged after exercise, while trimethyl‐ammonium groups increased. This is presented in the accompanying paper. In conclusion, a systematic comparison of metabolic changes in cross sections of the upper and lower leg was performed. The results imply that pre‐exercise IMCL levels determine the degree of IMCL depletion after exercise. Magn Reson Med, 2012.

Higher pulmonary artery pressure in children than in adults upon fast ascent to high altitude

The response of pulmonary artery pressure to high altitude has not been studied in children. It is also not known whether the individual response is hereditary. Therefore, the response of pulmonary artery pressure to high altitude was measured in pre-pubertal children in comparison to that in their biological fathers. Echocardiography was performed at 450 m and over 3 days at 3,450 m. Systolic pulmonary artery pressure was estimated from the pressure gradient of tricuspid regurgitation. The increase in pulmonary artery pressure in children was greater than that in adults at day 1 of high altitude (15.5±9.1 versus 7.9±6.4 mmHg), but returned to adult levels on day 2. The increase in pulmonary artery pressure from low to high altitude of each child correlated with that in the father. Pre-pubertal children transiently develop greater pulmonary hypertension than their fathers when exposed to high altitude. The individual response of pulmonary pressure to high altitude seems to be at least partly hereditary.

Noninvasive measurement of muscle high-energy phosphates and glycogen concentrations in elite soccer players by 31P- and 13C-MRS.

PURPOSE The purpose of this study was to measure noninvasively the absolute concentrations of muscle adenosine triphosphate [ATP], phosphocreatine [PCr], inorganic phosphate (Pi), and glycogen [Gly] of elite soccer players. METHODS Magnetic resonance spectroscopy (31P- and 13C-MRS) was used to measure the concentrations of metabolites in the calf muscles of 18 young male players [age = 17.5 +/- 1.0 (SD) yr]. RESULTS Average muscle [PCr] and [ATP] were 17.8 +/- 3.3 and 6.0 +/- 1.2 mmol x (kg wet weight)(-1), respectively. The ratios of Pi/PCr and PCr/ATP were 0.15 +/- 0.05 and 3.00 +/- 0.26, respectively. The muscle [Gly] was 144 +/- 54 mmol x (kg wet weight)(-1). There was a high correlation (r = 0.93, P < 0.0001) between muscle ATP and PCr concentrations, but there was no correlation between [Gly] and [PCr] or [ATP]. The concentrations of the different metabolites determined in the present study with noninvasive MRS methods were within the ranges of values reported in human muscle from biochemical analysis of muscle biopsies. CONCLUSION MRS methods can be utilized to assess noninvasively the muscle energetic status of elite soccer players during a soccer season. The high correlation between ATP and PCr might be indicative of fiber type differences in the content of these two metabolites.

Short-term cardiorespiratory adaptation to high altitude in children compared with adults.

As short‐term cardiorespiratory adaptation to high altitude (HA) exposure has not yet been studied in children, we assessed acute mountain sickness (AMS), hypoxic ventilatory response (HVR) at rest and maximal exercise capacity (CPET) at low altitude (LA) and HA in pre‐pubertal children and their fathers. Twenty father–child pairs (11 ± 1 years and 44 ± 4 years) were tested at LA (450 m) and HA (3450 m) at days 1, 2, and 3 after fast ascent (HA1/2/3). HVR was measured at rest and CPET was performed on a cycle ergometer. AMS severity was mild to moderate with no differences between generations. HVR was higher in children than adults at LA and increased at HA similarly in both groups. Peak oxygen uptake (VO2peak) relative to body weight was similar in children and adults at LA and decreased significantly by 20% in both groups at HA; maximal heart rate did not change at HA in children while it decreased by 16% in adults (P < 0.001). Changes in HVR and VO2peak from LA to HA were correlated among the biological child–father pairs. In conclusion, cardiorespiratory adaptation to altitude seems to be at least partly hereditary. Even though children and their fathers lose similar fractions of aerobic capacity going to high altitude, the mechanisms might be different.

Skeletal muscle 1H MRSI before and after prolonged exercise. II. visibility of free carnitine

Carnitine (Car) buffers excess acetyl‐CoA through the formation of acetylCar (AcCar). AcCars acetyl group (AG‐AcCar) gives rise to a peak at 2.13 ppm in 1H MR spectra of skeletal muscle, whereas the trimethylammonium (TMA) groups of both, AcCar and Car, are thought to contribute to the TMA peak at 3.23 ppm. Surprisingly, in previous studies both resonances, AG‐AcCar and TMA, increased after exercise. The aim of this study was to assess if the exercise‐related TMA increase correlated with AcCar production. Magnetic resonance spectroscopic imaging (pulse repetition time/echo time = 1200/35 ms) was performed before and after prolonged exercise in the lower leg and thigh of eight runners and eight cyclists, respectively. TMA and AG‐AcCar increased after exercise (P < 0.001). TMAs increase correlated with the AG‐AcCar increase (R2 = 0.73, P < 0.001, lower leg; R2 = 0.28, P < 0.001, thigh). The correlation of ΔTMA with ΔAG‐AcCar suggests that the TMA increase is due to AcCar formation. As total Car (Car + AcCar) remains unchanged with exercise, these findings suggest that the contribution of free Car to the TMA peak is limited and, therefore, is partly invisible in muscle 1H MR spectra. This indicates that the biochemically relevant cytosolic content of free Car is considerably lower than the overall concentration determined by radioisotopic assays, a potentially important result with respect to regulation of substrate oxidation. Magn Reson Med, 2012.