This study compared muscle glycogen recovery after depletion of similar to
50 mmol/l (Delta Gly) from normal (Nor) resting levels (63.2 +/- 2.8 mmol/l
) with recovery after depiction of similar to 50 mmol/l from a glycogen-loa
ded (GL) state (99.3 +/- 4.0 mmol/l) in 12 healthy, untrained subjects (5 m
en, 7 women). To glycogen load, a 7-day carbohydrate-loading protocol incre
ased muscle glycogen 1.6 +/- 0.2-fold (P less than or equal to 0.01). GL su
bjects then performed plantar flexion (single-leg toe raises) at 50 +/- 3%
of maximum voluntary contraction (MVC) to yield Delta Gly = 48.0 +/- 1.3 mm
ol/l. The Nor trial, performed on a separate occasion, yielded Delta Gly =
47.5 +/- 4.5 mmol/l. interleaved natural abundance C-13-P-31-NMR spectra we
re acquired and quantified before exercise and during 5 h of recovery immed
iately after exercise. During the initial 15 min after exercise, glycogen r
ecovery in the GL trial was rapid (32.9 +/- 8.9 mmol.l(-1).h(-1)) compared
with the Nor trial (15.9 +/- 6.9 mmol.l(-1).h(-1)). During the next 45 min,
GL glycogen synthesis was not as rapid as in the Nor trial (0.9 +/- 2.5 mm
ol.l(-1).h(-1) for GL; 14.7 +/- 3.0 mmol.l(-1).h(-1) for Nor; P less than o
r equal to 0.005) despite similar glucose 6-phosphate levels. During extend
ed recovery (60-300 min), reduced GL recovery rates continued (1.3 +/- 0.5
mmol.l(-1).h(-1) for GL; 3.9 +/- 0.3 mmol.l(-1).h(-1) for Nor; P less than
or equal to 0.001). We conclude that glycogen recovery from heavy exercise
is controlled primarily by the remaining postexercise glycogen concentratio
n, with only a transient synthesis period when glycogen levels are not seve
rely reduced.