Abstract
Muscle metabolism and force production were studied in sprint
trained runners, endurance trained runners and in untrained subjects, using
31 P-MRS. 31 P-spectra were obtained at a time resolution
of 5 s during four maximal isometric contractions of 30-sec duration,
interspersed by 60-sec recovery intervals. Resting CrP/ATP ratio averaged
3.3 ± 0.3, with no difference among the three groups. The sprint trained subjects showed about
20 % larger contraction forces in contraction bouts 1 and 2
(p < 0.05). The groups differed with respect to CrP breakdown
(p < 0.05), with sprinters demonstrating about
75 % breakdown in each contraction compared to about
60 % and 40 % for untrained and endurance trained
subjects, respectively (p < 0.05). The endurance trained
runners showed almost twice as fast CrP recovery
(t1/2 = 12.5 ± 1.5)
compared to sprint trained
(t1/2 = 22.5 ± 2.53) and
untrained subjects
(t1/2 = 26.4 ± 2.8). From
the initial rate of CrP resynthesis the rate of maximal aerobic ATP synthesis
was estimated to 0.74 ± 0.07,
0.73 ± 0.10 and
0.33 ± 0.07 mmol
ATP × kg-1 wet
muscle × sec-1 for sprint trained, endurance
trained and untrained subjects, respectively.
Only the sprint trained and the untrained subjects displayed a
significant drop in pH and only during the first of the four contractions,
about 0.2 and 0.1 pH units, respectively, indicating that only under
those contractions was the glycolytic proton production larger than the proton
consumption by the CK reaction. Also, in the first contraction the energy cost
of contraction was higher for the sprinters compared to the two other
groups.
The simple 31 P-MRS protocol used in the present study
demonstrates marked differences in force production, aerobic as well as
anaerobic muscle metabolism, clearly allowing differentiation between endurance
trained, sprint trained and untrained subjects.
Key words
Anaerobic energy - intermittent work - training -
31 P-MRS
References
31 P- NMR.
Magn Reson Med.
1984;
1
307-325
ljohansen@health.sdu.dk
