Progressive resistance training (PRT) in the elderly has commonly used ATPase histochemistry to evaluate fiber type changes, but evidence shows there are myosin heavy chain (MHC) hybrids in aging muscle that cannot be classified by histochemistry. The purpose of this study was to assess the MHC and whole muscle alterations following a 12-week PRT protocol. Seven healthy men (age=74.0±4.7, weight=74.6±13.5kg) underwent testing for 1-repetition maximum (1-RM), whole muscle (thigh) crosssectional area (CSA) by computed tomography, and a needle muscle biopsy from the vastus lateralis for analysis of MHC, pre- and post-training. The PRT consisted of 2 sets of 10 repetitions, and a third set to volitional exhaustion at 80% 1-RM, 3 days per week for 12 weeks. Muscle ATPase histochemistry analysis for distribution did not significantly differ following training. Muscle samples were freeze dried and dissected for MHC analysis (sodium dodecyl sulfate-polyacrylamide gel electrophoresis (5% gel) and silver stained; 224.0±11.2 and 213.0±8.1 fibers/subject pre-/post-training; total fibers analyzed=3059). MHC analysis demonstrated significant increases in MHC I proportion (10.4%; P<0.05), and significant decreases in MHC UIIa (9.0%; P<0.05), UIIa/x (0.9%; P<0.05), and IIa/x (8.9%; P<0.05) isofroms, along with no change in the MHC Ila and IIx isoforms, pre- versus post-training. In addition, 1-RM (51.9%; P<0.05) and CSA (5.9%; P<0.05) increased from pre- to post-testing. This data supports previous whole muscle changes, more important, is the increase in MHC I and decrease in MHC I/IIa, I/IIa/IIx, and IIa/x hybrids. The myosin light chain 3f (MLC3f) to MLC 2 ratio did not change with the PRT in either the MHC I or MHC IIa isoforms, although there was a significantly greater amount of MLC 3f in the MHC Ila versus the MHC I fibers (p<0.05), pre- and post-training. The myosin isofrom data provides support that aging muscle has the plasticity to adapt in a manner unlike that of young muscle. / School of Physical Education

The purpose of this investigation was to examine differences under resting conditions (baseline) and after a bout of resistance exercise, in the total amount and the activation (phosphorylation) of the p42/44 MAPK signaling cascade proteins (ERK 1/2, p90RSK, and MNK 1) in young and old men. Eight young (22±1 yr) and eight old (79±3 yr) men underwent a resting muscle biopsy of the vastus lateralis, then a knee extensor resistance exercise session (29 contractions at -70% of max), followed by a post-exercise biopsy. The total protein expression and phosphorylation state for ERK 1/2, p90RSK, and MNK 1 was determined by Western immunoblot analysis. Total protein expression of ERK 1/2 and MNK 1 were not different between the young and old, before and after exercise. The resistance exercise bout caused an increase in phosphorylation of the ERK 1/2, p90RSK, and MNK 1 proteins (73, 95, and 61%, respectively; P<0.05) in the young men. Conversely, the older men showed a decrease in ERK 1/2, p90RSK, and MNK1 phosphorylation (-48, -62, and -37%, respectively; P<0.05) after the exercise bout (versus old pre). Although, the old men displayed higher pre-exercise phosphorylation of these proteins versus young pre-exercise (131, 248, and 74%, respectively; P<0.05). This investigation is the first to provide evidence that MAPK signaling pathways differentially respond under resting and exercise conditions in skeletal muscle of young and old men. These findings may have implications for other processes (e.g. transcription and translation) involved in skeletal muscle type and growth, when examining the changes occurring with aging muscle before and after resistance exercise/training. / School of Physical Education