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Lookup NU author(s): Dr Linda Heskamp
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The rate of phosphocreatine (PCr) recovery (k(PCr)) after exercise, characterizing muscle oxidative capacity, is traditionally assessed with unlocalized P-31 magnetic resonance spectroscopy (MRS) using a single surface coil. However, because of intramuscular variation in fibre type and oxygen supply, k(PCr) may be non-uniform within muscles. We tested this along the length of the tibialis anterior (TA) muscle in 10male volunteers. For this purpose, we employed a 3T MR system with a P-31/H-1 volume transmit coil combined with a home-built P-31 phased-array receive probe, consisting of five coil elements covering the TA muscle length. Mono-exponential k(PCr) was determined for all coil elements after 40s of submaximal isometric dorsiflexion (SUBMAX) and incremental exercise to exhaustion (EXH). In addition, muscle functional MRI (H-1 mfMRI) was performed using the volume coil after another 40s of SUBMAX. A strong gradient in k(PCr) was observed along the TA (P<0.001), being two times higher proximally vs. distally during SUBMAX and EXH. Statistical analysis showed that this gradient cannot be explained by pH variations. A similar gradient was seen in the slope of the initial post-exercise H-1 mfMRI signal change, which was higher proximally than distally in both the TA and the extensor digitorum longus (P<0.001) and strongly correlated with k(PCr). The pronounced differences along the TA in functional oxidative capacity identify regional variation in the physiological demand of this muscle during everyday activities and have implications for the bio-energetic assessment of interventions to modify its performance and of neuromuscular disorders involving the TA.
Author(s): Boss A, Heskamp L, Breukels V, Bains LJ, van Uden MJ, Heerschap A
Publication type: Article
Publication status: Published
Journal: Journal of Physiology
Print publication date: 15/04/2018
Online publication date: 18/02/2018
Acceptance date: 12/02/2018
ISSN (print): 0022-3751
ISSN (electronic): 1469-7793
Publisher: Wiley-Blackwell Publishing Ltd.
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