Noninvasive Monitoring of Training Induced Muscle Adaptation with ³¹P-MRS: Fibre Type Shifts Correlate with Metabolic Changes

Table 3

Relative contents of the high energy phosphates and the fibre type distribution for the 4 measurement points. ³¹P-MRS measurements and biopsies were performed initially (𝑡₀) and after a period of speed-strength (𝑡_𝑆), endurance (𝑡_𝐸), and de-training (𝑡_𝐷). Fibre types were classified into slow-twitch more oxidative type I and fast-twitch more glycolytic type II with subtypes IIa and IIb (ATPase reaction).

	𝑡0			𝑡𝑆			𝑡𝐸			𝑡𝐷
	Median ± SE	Min	Max	Median ± SE	Min	Max	Median ± SE	Min	Max	Median ± SE	Min	Max
MRS
[PCr]/[P𝑖]	7.37±0.51	4.91	9.16	8.14±0.50	5.76	9.56	7.14±0.49	6.10	10.09	8.42±0.64	6.27	11.38
[PCr]/[βATP]	4.17±0.21	2.95	4.70	4.54±0.31	3.08	4.97	4.59±0.22	3.45	4.82	4.49±0.21	3.41	5.14
[PCr + P𝑖]/[βATP]	4.80±0.14	4.26	5.35	5.01±0.23	3.61	5.52	5.29±0.23	3.82	5.55	5.11±0.25	3.94	5.73
Biopsy
Type I (%)	71.9±6.26	33.0	85.3	66.4±5.89	43.5	83.8	77.1±3.48	55.8	83.5	73.8±7.75	21.8	83.8
Type II (%)	28.1±2.98	14.7	38.1	33.6±5.89	16.2	56.5	22.9±3.48	16.5	44.2	26.2±7.75	16.2	78.2
Type IIa (%)	23.6±3.30	12.4	37.4	32.0±4.83	15.7	48.4	22.1±2.62	11.9	34.0	23.5±6.54	15.7	65.5
Type IIb (%)	2.0±0.65	0.0	5.1	5.3±1.90	0.5	11.7	5.2±1.26	0.5	10.2	1.9±1.72	0.5	12.7

SE: standard error. MIN: minimum. MAX: maximum. 𝑡₀: preinterventional. 𝑡_𝑆: after speed-strength training; 𝑡_𝐸: after endurance training. 𝑡_𝐷: after de-training.