Effects of chromium supplementation on glycogen synthesis after high-intensity exercise.
OBJECTIVE
Chromium enhances insulin signaling and insulin-mediated glucose uptake in cultured cells. We investigated the effect of chromium on glycogen synthesis and insulin signaling in humans.


METHODS
Sixteen overweight men (BMI = 31.1 +/- 3.0 kg.m) were randomly assigned to supplement with 600 microg.d chromium as picolinate (Cr; N = 8) or a placebo (Pl; N = 8). After 4 wk of supplementation, subjects performed a supramaximal bout of cycling exercise to deplete muscle glycogen, which was followed by high-glycemic carbohydrate feedings for the next 24 h. Muscle biopsies were obtained at rest, immediately after exercise, and 2 and 24 h after exercise.


RESULTS
Elevations in glucose and insulin during recovery were not different, but the lactate response was significantly higher in Cr. There was a significant depletion in glycogen immediately after exercise, an increase at 2 h, and a further increase above rest at 24 h (P < 0.05). The rate of glycogen synthesis during the 2 h after exercise was not different between groups (Cr: 25.8 +/- 8.0 and Pl: 17.1 +/- 4.7 mmol.kg.h). Glycogen synthase activity was significantly increased immediately after exercise in both groups. Muscle phosphatidylinositol 3-kinase (PI 3-kinase) activity decreased immediately after exercise and increased at 2 h (P < 0.05), with a trend for a lower PI 3-kinase response in Cr (P = 0.08).


CONCLUSIONS
Chromium supplementation did not augment glycogen synthesis during recovery from high-intensity exercise and high-carbohydrate feeding, although there was a trend for lower PI 3-kinase activity.
Volek
Jeff S
JS
Human Performance Laboratory, Department of Kinesiology, University of Connecticut, Storrs, CT 06269-1110, USA. jeff.volek@uconn.edu
Silvestre
Ricardo
R
Kirwan
John P
JP
Sharman
Matthew J
MJ
Judelson
Daniel A
DA
Spiering
Barry A
BA
Vingren
Jakob L
JL
Maresh
Carl M
CM
Vanheest
Jaci L
JL
Kraemer
William J
WJ
D000328:Adult; D001707:Biopsy, Needle; D050528:Diet, Carbohydrate-Restricted; D019587:Dietary Supplements; D004311:Double-Blind Method; D005080:Exercise Test; D006003:Glycogen / Q000096:biosynthesis*; D006801:Humans; D007502:Iron Chelating Agents / Q000494:pharmacology*; D019344:Lactic Acid / Q000097:blood; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism / Q000473:pathology; D050177:Overweight; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010807:Physical Endurance; D010848:Picolinic Acids / Q000494:pharmacology*; D013997:Time Factors
D007502:Iron Chelating Agents; D010848:Picolinic Acids; D019344:Lactic Acid; D006003:Glycogen; D019869:Phosphatidylinositol 3-Kinases; C030614:picolinic acid