HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Free Full Text (PDF) Free All Versions of this Article: 102/6/2232    most recent 00024.2007v1 Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (12) Citing Articles via Google Scholar Google Scholar Articles by Bamman, M. M. Articles by Cross, J. M. Search for Related Content PubMed PubMed Citation Articles by Bamman, M. M. Articles by Cross, J. M.

Cluster analysis tests the importance of myogenic gene expression during myofiber hypertrophy in humans

Departments of ¹Physiology and Biophysics and of ³Surgery, and ⁴Medical Scientist Training Program, The University of Alabama at Birmingham; and ²Geriatric Research, Education, and Clinical Center, Birmingham Veterans Affairs Medical Center, Birmingham, Alabama

Submitted 6 January 2007 ; accepted in final form 19 March 2007

We applied K-means cluster analysis to test the hypothesis that muscle-specific factors known to modulate protein synthesis and satellite cell activity would be differentially expressed during progressive resistance training (PRT, 16 wk) in 66 human subjects experiencing extreme, modest, and failed myofiber hypertrophy. Muscle mRNA expression of IGF-I isoform Ea (IGF-IEa), mechanogrowth factor (MGF, IGF-IEc), myogenin, and MyoD were assessed in muscle biopsies collected at baseline (T1) and 24 h after the first (T2) and last (T3) loading bouts from previously untrained subjects clustered as extreme responders (Xtr, n = 17), modest responders (Mod, n = 32), and nonresponders (Non, n = 17) based on mean myofiber hypertrophy. Myofiber growth averaged 2,475 µm² in Xtr, 1,111 µm² in Mod, and –16 µm² in Non. Main training effects revealed increases in all transcripts (46–83%, P < 0.005). For the entire cohort, IGF-IEa, MGF, and myogenin mRNAs were upregulated by T2 (P < 0.05), while MyoD did not increase significantly until T3 (P < 0.001). Within clusters, MGF and myogenin upregulation was robust in Xtr (126% and 65%) and Mod (73% and 41%) vs. no changes in Non. While significant in all clusters by T3, IGF-IEa increased most in Xtr (105%) and least in Non (44%). Although MyoD expression increased overall, no changes within clusters were detected. We reveal for the first time that MGF and myogenin transcripts are differentially expressed in subjects experiencing varying degrees of PRT-mediated myofiber hypertrophy. The data strongly suggest the load-mediated induction of these genes may initiate important actions necessary to promote myofiber growth during PRT, while the role of MyoD is less clear.

muscle growth; myogenin; insulin-like growth factor I; muscle fiber

This article has been cited by other articles:

				D. L. Mayhew, J.-s. Kim, J. M. Cross, A. A. Ferrando, and M. M. Bamman Translational signaling responses preceding resistance training-mediated myofiber hypertrophy in young and old humans J Appl Physiol, November 1, 2009; 107(5): 1655 - 1662. [Abstract] [Full Text] [PDF]

				R. A. Dennis, H. Zhu, P. M. Kortebein, H. M. Bush, J. F. Harvey, D. H. Sullivan, and C. A. Peterson Muscle expression of genes associated with inflammation, growth, and remodeling is strongly correlated in older adults with resistance training outcomes Physiol Genomics, July 9, 2009; 38(2): 169 - 175. [Abstract] [Full Text] [PDF]

				M. J. Drummond, M. Miyazaki, H. C. Dreyer, B. Pennings, S. Dhanani, E. Volpi, K. A. Esser, and B. B. Rasmussen Expression of growth-related genes in young and older human skeletal muscle following an acute stimulation of protein synthesis J Appl Physiol, April 1, 2009; 106(4): 1403 - 1411. [Abstract] [Full Text] [PDF]

				J. K. Petrella, J.-s. Kim, D. L. Mayhew, J. M. Cross, and M. M. Bamman Potent myofiber hypertrophy during resistance training in humans is associated with satellite cell-mediated myonuclear addition: a cluster analysis J Appl Physiol, June 1, 2008; 104(6): 1736 - 1742. [Abstract] [Full Text] [PDF]

				D. J. Kosek and M. M. Bamman Modulation of the dystrophin-associated protein complex in response to resistance training in young and older men J Appl Physiol, May 1, 2008; 104(5): 1476 - 1484. [Abstract] [Full Text] [PDF]

				S. M. Roth Perspective on the future use of genomics in exercise prescription J Appl Physiol, April 1, 2008; 104(4): 1243 - 1245. [Full Text] [PDF]

				M. M. Bamman Reply to Dr. Heinemeier J Appl Physiol, November 1, 2007; 103(5): 1915 - 1915. [Full Text] [PDF]

				J.-s. Kim, J. K. Petrella, J. M. Cross, and M. M. Bamman Load-mediated downregulation of myostatin mRNA is not sufficient to promote myofiber hypertrophy in humans: a cluster analysis J Appl Physiol, November 1, 2007; 103(5): 1488 - 1495. [Abstract] [Full Text] [PDF]