Ulrika Raue

Single muscle fiber adaptations to resistance training in old (>80 yr) men: evidence for limited skeletal muscle plasticity

The purpose of this study was to investigate whole muscle and single muscle fiber adaptations in very old men in response to progressive resistance training (PRT). Six healthy independently living old men (82 +/- 1 yr; range 80-86 yr, 74 +/- 4 kg) resistance-trained the knee extensors (3 sets, 10 repetitions) at approximately 70% one repetition maximum 3 days/wk for 12 wk. Whole thigh muscle cross-sectional area (CSA) was assessed before and after PRT using computed tomography (CT). Muscle biopsies were obtained from the vastus lateralis before and after the PRT program. Isolated myosin heavy chain (MHC) I and IIa single muscle fibers (n = 267; 142 pre; 125 post) were studied for diameter, peak tension, shortening velocity, and power. An additional set of isolated single muscle fibers (n = 2,215; 1,202 pre; 1,013 post) was used to identify MHC distribution. One repetition maximum knee extensor strength increased (P < 0.05) 23 +/- 4 kg (56 +/- 4 to 79 +/- 7 kg; 41%). Muscle CSA increased (P < 0.05) 3 +/- 1 cm2 (120 +/- 7 to 123 +/- 7 cm2; 2.5%). Single muscle fiber contractile function and MHC distribution were unaltered with PRT. These data indicate limited muscle plasticity at the single-muscle fiber level with a resistance-training program among the very old. The minor increases in whole muscle CSA coupled with the static nature of the myocellular profile indicate that the strength gains were primarily neurological. These data contrast typical muscle responses to resistance training in young ( approximately 20 yr) and old ( approximately 70 yr) humans and indicate that the physiological regulation of muscle remodeling is adversely modified in the oldest old.

Improvements in whole muscle and myocellular function are limited with high-intensity resistance training in octogenarian women.

Advanced sarcopenia is prevalent among octogenarian women; yet little is known about myocellular quality and plasticity in this cohort. The aim of this investigation was to examine single muscle fiber contractile function and whole muscle characteristics before and after 12 wk of high-intensity progressive resistance training (PRT) in very old (85 +/- 1 yr) women (OW, n = 6). Young women [YW (21 +/- 2 yr old), n = 9] were included as a control group. Whole muscle strength [1 repetition maximum (RM)] and size (CT scans) were assessed before and after PRT. Functional experiments (size, peak force, velocity, and power) were performed on vastus lateralis myosin heavy chain (MHC) I and IIa muscle fibers before and after PRT. With PRT, 1-RM strength increased (P < 0.05) in YW (36%) and OW (26%). Thigh muscle cross-sectional area increased (5%) in YW (P < 0.05), but thigh muscle did not hypertrophy in OW. Before PRT, there were no differences in single-fiber parameters between YW and OW. With PRT, MHC IIa fiber size (28%), peak force (31%), and power (28%) improved, but no changes were observed in MHC I fibers, in YW (P < 0.05). There were no improvements in MHC I or IIa single-fiber function in OW. These data show that the myocellular functional profile in OW is similar to that in YW but that OW have a blunted hypertrophic response to PRT at the whole muscle and myocellular level. The limited myocellular plasticity in OW with PRT contrasts with that in YW and previous PRT studies in elderly women only a decade younger. These data suggest that attempts to greatly enhance skeletal muscle mass and function should begin before 80 yr of age.

Protein synthesis and the expression of growth-related genes are altered by running in human vastus lateralis and soleus muscles

Recent evidence suggests aerobic exercise may help preserve soleus muscle mass during unloading. The purpose of this investigation was to examine the muscle-specific metabolic response to running as it relates to muscle growth. Mixed-muscle protein synthesis [fractional synthetic rate (FSR)] and gene expression (GE) were examined in the vastus lateralis (VL) and soleus (SOL) muscles from eight men (26 +/- 2 yr; Vo(2max) 63 +/- 2 ml.kg(-1).min(-1)) before and after a 45-min level-grade treadmill run at 77 +/- 1% intensity. Muscle glycogen utilization was similar between muscles. Resting FSR was similar between the VL (0.080 +/- 0.007 %/h) and SOL (0.086 +/- 0.008 %/h) and was higher (P < 0.05) 24 h postexercise compared with rest for both muscles. The absolute change in FSR was not different between muscles (0.030 +/- 0.007 vs. 0.037 +/- 0.012 %/h for VL and SOL). At baseline, myostatin GE was approximately twofold higher (P < 0.05) in SOL compared with VL, while no other muscle-specific differences in GE were present. After running, myostatin GE was suppressed (P < 0.05) in both muscles at 4 h and was higher (P < 0.05) than baseline at 24 h for VL only. Muscle regulatory factor 4 mRNA was elevated (P < 0.05) at 4 h in both SOL and VL; MyoD and peroxisome-proliferator-activated receptor-gamma coactivator-1alpha (PGC-1alpha) were higher (P < 0.05) at 4 h, and forkhead box [FOXO]3A was higher at 24 h in SOL only, while muscle-RING-finger protein-1 (MuRF-1) was higher (P < 0.05) at 4 h in VL only. Myogenin and atrogin-1 GE were unaltered. The similar increases between muscles in FSR support running as part of the exercise countermeasure to preserve soleus mass during unloading. The subtle differences in GE suggest a potential mechanism for muscle-specific adaptations to chronic run training.

Resistance Exercise, Skeletal Muscle FOXO3A, and 85-Year-Old Women

This investigation examined Akt-FOXO3A signaling in young women (YW) and old women (OW) before and after 12 weeks of high-intensity resistance training. Muscle biopsies were taken from the vastus lateralis before and immediately after resistance exercise (RE) in the untrained and trained states. In response to RE in YW and OW, phospho Akt Thr308 increased in untrained and trained states, with no change on Ser473 site. FOXO3A-Ser253 site was dephosphorylated in untrained state among YW and OW, and nuclear phospho-FOXO3A increased mainly in YW in trained state. In the basal state, OW displayed lower cytosolic phospho-FOXO3A before training, higher total nuclear FOXO3A, and a trend for higher nuclear-to-cytosolic FOXO3A ratio versus YW after 12 weeks. Basal level MuRF-1 and myostatin mRNA decreased in YW, while OW increased myostatin mRNA after 12-weeks. These data suggest that FOXO3A signaling and FOXO3A-related target gene expression are altered in OW and may partially explain the attenuated training adaptations previously reported in these octogenarian women.

Human Skeletal Muscle Fiber Type Specific Protein Content

The aim of this project was to develop a method to assess fiber type specific protein content across the continuum of human skeletal muscle fibers. Individual vastus lateralis muscle fibers (n = 264) were clipped into two portions: one for sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) fiber typing and one for Western blot protein identification. Following fiber type determination, fiber segments were combined into fiber type specific pools (∼20 fibers/pool) and measured for total protein quantity, glyceraldehyde 3-phosphate dehydrogenase (GAPDH), citrate synthase (CS), and total p38 content. GAPDH content was 64, 54, 160, and 138% more abundant in myosin heavy chain (MHC) I/IIa, MHC IIa, MHC IIa/IIx, and MHC IIx fibers, respectively, when compared with MHC I. Inversely, CS content was 528, 472, 242, and 47% more abundant in MHC I, MHC I/IIa, MHC IIa, and MHC IIa/IIx fibers, respectively, when compared with MHC IIx. Total p38 content was 87% greater in MHC IIa versus MHC I fibers. These data and this approach establish a reliable method for human skeletal muscle fiber type specific protein analysis. Initial results show that particular proteins exist in a hierarchal fashion throughout the continuum of human skeletal muscle fiber types, further highlighting the necessity of fiber type specific analysis.

Skeletal muscle signature of a champion sprint runner

We had the unique opportunity to study the skeletal muscle characteristics, at the single fiber level, of a world champion sprint runner who is the current indoor world record holder in the 60-m hurdles (7.30 s) and former world record holder in 110-m hurdles (12.91 s). Muscle biopsies were obtained from the vastus lateralis at rest and 4 h after a high-intensity exercise challenge (4 × 7 repetitions of resistance exercise). Single muscle fiber analyses were conducted for fiber type distribution (myosin heavy chain, MHC), fiber size, contractile function (strength, speed, and power) and mRNA expression (before and after the exercise bout). The world-class sprinters leg muscle had a high abundance (24%) of the pure MHC IIx muscle fibers with a total fast-twitch fiber population of 71%. Power output of the MHC IIx fibers (35.1 ± 1.4 W/l) was 2-fold higher than MHC IIa fibers (17.1 ± 0.5 W/l) and 14-fold greater than MHC I fibers (2.5 ± 0.1 W/l). Additionally, the MHC IIx fibers were highly responsive to intense exercise at the transcriptional level for genes involved with muscle growth and remodeling (Fn14 and myostatin). To our knowledge, the abundance of pure MHC IIx muscle fibers is the highest observed in an elite sprinter. Further, the power output of the MHC IIa and MHC IIx muscle fibers was greater than any human values reported to date. These data provide a myocellular basis for the high level of sprinting success achieved by this individual.

Skeletal muscle plasticity with marathon training in novice runners

The purpose of this study was to investigate leg muscle adaptation in runners preparing for their first marathon. Soleus and vastus lateralis (VL) biopsies were obtained from six recreational runners (23 ± 1 years, 61 ± 3u2003kg) before (T1), after 13 weeks of run training (T2), and after 3 weeks of taper and marathon (T3). Single muscle fiber size, contractile function (strength, speed, and power) and oxidative enzyme activity [citrate synthase (CS)] were measured at all three time points, and fiber type distribution was determined before and after the 16‐week intervention. Training increased VO2max∼9% (P<0.05). All soleus parameters were unchanged. VL MHC I fiber diameter increased (+8%; P<0.05) from T1 to T2. VL MHC I Vo (−12%), MHC I power (−22%) and MHC IIa power (−29%) were reduced from T1 to T2 (P<0.05). No changes in VL single fiber contractile properties were observed from T2 to T3. No change was observed in soleus CS activity, whereas VL CS activity increased 66% (P<0.05). Our observations indicate that modest marathon training elicits very specific skeletal muscle adaptations that likely support the ability to perform 42.2u2003km of continuous running – further strengthening the existing body of evidence for skeletal muscle specificity.

Single muscle fiber gene expression with run taper.

This study evaluated gene expression changes in gastrocnemius slow-twitch myosin heavy chain I (MHC I) and fast-twitch (MHC IIa) muscle fibers of collegiate cross-country runners (nu200a=u200a6, 20±1 y, VO2maxu200a=u200a70±1 ml•kg−1•min−1) during two distinct training phases. In a controlled environment, runners performed identical 8 kilometer runs (30∶18±0∶30 min:s, 89±1% HRmax) while in heavy training (∼72 km/wk) and following a 3 wk taper. Training volume during the taper leading into peak competition was reduced ∼50% which resulted in improved race times and greater cross-section and improved function of MHC IIa fibers. Single muscle fibers were isolated from pre and 4 hour post run biopsies in heavily trained and tapered states to examine the dynamic acute exercise response of the growth-related genes Fibroblast growth factor-inducible 14 (FN14), Myostatin (MSTN), Heat shock protein 72 (HSP72), Muscle ring-finger protein-1 (MURF1), Myogenic factor 6 (MRF4), and Insulin-like growth factor 1 (IGF1) via qPCR. FN14 increased 4.3-fold in MHC IIa fibers with exercise in the tapered state (P<0.05). MSTN was suppressed with exercise in both fiber types and training states (P<0.05) while MURF1 and HSP72 responded to running in MHC IIa and I fibers, respectively, regardless of training state (P<0.05). Robust induction of FN14 (previously shown to strongly correlate with hypertrophy) and greater overall transcriptional flexibility with exercise in the tapered state provides an initial molecular basis for fast-twitch muscle fiber performance gains previously observed after taper in competitive endurance athletes.

Improved Single Muscle Fiber Quality in the Oldest-Old

We examined single muscle fiber contractile function of the oldest-old (3F/2M, 89 ± 1 yr old) enrolled in The Health, Aging, and Body Composition Study (The Health ABC Study). Vastus lateralis muscle biopsies were obtained and single muscle fiber function was determined (n = 105) prior to myosin heavy chain (MHC) isoform identification with sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Cross-sectional area of MHC I muscle fibers (5,576 ± 333 μm2; n = 58) was 21% larger (P < 0.05) than MHC IIa fibers (4,518 ± 386 μm2; n = 47). Normalized power (an indicator of muscle fiber quality incorporating size, strength, and speed) of MHC I and IIa muscle fibers was 2.3 ± 0.1 and 17.4 ± 0.8 W/l, respectively. Compared with previous research from our lab using identical procedures, MHC I normalized power was 28% higher than healthy 20 yr olds and similar to younger octogenarians (∼80 yr old). Normalized power of MHC IIa fibers was 63% greater than 20 yr olds and 39% greater than younger octogenarians. These comparative data suggest that power output per unit size (i.e., muscle quality) of remaining muscle fibers improves with age, a phenomenon more pronounced in MHC IIa fibers. Age-related single muscle fiber quality improvements may be a compensatory mechanism to help offset decrements in whole muscle function.

TWEAK-Fn14 pathway activation after exercise in human skeletal muscle: insights from two exercise modes and a time course investigation

The cell surface receptor Fn14/TWEAKR was recently reported by our laboratory to be a prominent marker in the resistance exercise (RE) induced Transcriptome. The purpose of the present study was to extend our Transcriptome findings and investigate the gene and protein expression time course of markers in the TWEAK-Fn14 pathway following RE or run exercise (RUN). Vastus lateralis muscle biopsies were obtained from 6 RE subjects [25 ± 4 yr, 1-repetition maximum (RM): 99 ± 27 kg] pre- and 0, 1, 2, 4, 8, 12, and 24 h post RE (3 × 10 at 70% 1-RM). Lateral gastrocnemius biopsies were obtained from 6 RUN subjects [25 ± 4 yr, maximum oxygen uptake (V̇O2max): 63 ± 8 ml·kg(-1)·min(-1)] pre- and 0, 1, 2, 4, 8, 12, and 24 h after a 30-min RUN (75% V̇O2max). After RE, Fn14 gene and protein expression were induced (P < 0.05) and peaked at 8 and 12 h, respectively. Downstream markers analyzed showed evidence of TWEAK-Fn14 signaling through the alternative NF-κB pathway after RE. After RUN, Fn14 gene expression was induced (P < 0.05) to a much lesser extent and peaked at 24 h. Fn14 protein expression was only measurable on a sporadic basis, and there was weak evidence of alternative NF-κB pathway signaling after RUN. TWEAK gene and protein expression were not influenced by either exercise mode. These are the first human data to show a transient activation of the TWEAK-Fn14 axis in the recovery from exercise, and our data suggest the level of activation is exercise mode dependent. Furthermore, our collective data support a myogenic role for TWEAK-Fn14 through the alternative NF-κB pathway in human skeletal muscle.