Myocellular basis for tapering in competitive distance runners

Exercise microdosing for skeletal muscle health applications to spaceflight

Findings from a recent 70-day bedrest investigation suggested intermittent exercise testing in the control group may have served as a partial countermeasure for skeletal muscle size, function, and fiber-type shifts. The purpose of the current study was to investigate the metabolic and skeletal muscle molecular responses to the testing protocols. Eight males (29 ± 2 yr) completed muscle power (6 × 4 s; peak muscle power: 1,369 ± 86 W) and V̇o2max (13 ± 1 min; 3.2 ± 0.2 L/min) tests on specially designed supine cycle ergometers during two separate trials. Blood catecholamines and lactate were measured pre-, immediately post-, and 4-h postexercise. Muscle homogenate and muscle fiber-type-specific [myosin heavy chain (MHC) I and MHC IIa] mRNA levels of exercise markers (myostatin, IκBα, myogenin, MuRF-1, ABRA, RRAD, Fn14, PDK4) and MHC I, IIa, and IIx were measured from vastus lateralis muscle biopsies obtained pre- and 4-h postexercise. The muscle power test altered (P ≤ 0.05) norepinephrine (+124%), epinephrine (+145%), lactate (+300%), and muscle homogenate mRNA (IκBα, myogenin, MuRF-1, RRAD, Fn14). The V̇o2max test altered (P ≤ 0.05) norepinephrine (+1,394%), epinephrine (+1,412%), lactate (+736%), and muscle homogenate mRNA (myostatin, IκBα, myogenin, MuRF-1, ABRA, RRAD, Fn14, PDK4). In general, both tests influenced MHC IIa muscle fibers more than MHC I with respect to the number of genes that responded and the magnitude of response. Both tests also influenced MHC mRNA expression in a muscle fiber-type-specific manner. These findings provide unique insights into the adaptive response of skeletal muscle to small doses of exercise and could help shape exercise dosing for astronauts and Earth-based individuals.NEW & NOTEWORTHY Declines in skeletal muscle health are a concern for astronauts on long-duration spaceflights. The current findings add to the growing body of exercise countermeasures data, suggesting that small doses of specific exercise can be beneficial for certain aspects of skeletal muscle health. This information can be used in conjunction with other components of existing exercise programs for astronauts and might translate to other areas focused on skeletal muscle health (e.g., sports medicine, rehabilitation, aging).

Fast and slow muscle fiber transcriptome dynamics with lifelong endurance exercise

We investigated fast and slow muscle fiber transcriptome exercise dynamics among three groups of men: lifelong exercisers (LLE, n = 8, 74 ± 1 yr), old healthy nonexercisers (OH, n = 9, 75 ± 1 yr), and young exercisers (YE, n = 8, 25 ± 1 yr). On average, LLE had exercised ∼4 day·wk-1 for ∼8 h·wk-1 over 53 ± 2 years. Muscle biopsies were obtained pre- and 4 h postresistance exercise (3 × 10 knee extensions at 70% 1-RM). Fast and slow fiber size and function were assessed preexercise with fast and slow RNA-seq profiles examined pre- and postexercise. LLE fast fiber size was similar to OH, which was ∼30% smaller than YE (P < 0.05) with contractile function variables among groups, resulting in lower power in LLE (P < 0.05). LLE slow fibers were ∼30% larger and more powerful compared with YE and OH (P < 0.05). At the transcriptome level, fast fibers were more responsive to resistance exercise compared with slow fibers among all three cohorts (P < 0.05). Exercise induced a comprehensive biological response in fast fibers (P < 0.05) including transcription, signaling, skeletal muscle cell differentiation, and metabolism with vast differences among the groups. Fast fibers from YE exhibited a growth and metabolic signature, with LLE being primarily metabolic, and OH showing a strong stress-related response. In slow fibers, only LLE exhibited a biological response to exercise (P < 0.05), which was related to ketone and lipid metabolism. The divergent exercise transcriptome signatures provide novel insight into the molecular regulation in fast and slow fibers with age and exercise and suggest that the ∼5% weekly exercise time commitment of the lifelong exercisers provided a powerful investment for fast and slow muscle fiber metabolic health at the molecular level.NEW & NOTEWORTHY This study provides the first insights into fast and slow muscle fiber transcriptome dynamics with lifelong endurance exercise. The fast fibers were more responsive to exercise with divergent transcriptome signatures among young exercisers (growth and metabolic), lifelong exercisers (metabolic), and old healthy nonexercisers (stress). Only lifelong exercisers had a biological response in slow fibers (metabolic). These data provide novel insights into fast and slow muscle fiber health at the molecular level with age and exercise.

Coordinated Regulation of Myonuclear DNA Methylation, mRNA, and miRNA Levels Associates With the Metabolic Response to Rapid Synergist Ablation-Induced Skeletal Muscle Hypertrophy in Female Mice

The central dogma of molecular biology dictates the general flow of molecular information from DNA that leads to a functional cellular outcome. In skeletal muscle fibers, the extent to which global myonuclear transcriptional alterations, accounting for epigenetic and post-transcriptional influences, contribute to an adaptive stress response is not clearly defined. In this investigation, we leveraged an integrated analysis of the myonucleus-specific DNA methylome and transcriptome, as well as myonuclear small RNA profiling to molecularly define the early phase of skeletal muscle fiber hypertrophy. The analysis of myonucleus-specific mature microRNA and other small RNA species provides new directions for exploring muscle adaptation and complemented the methylation and transcriptional information. Our integrated multi-omics interrogation revealed a coordinated myonuclear molecular landscape during muscle loading that coincides with an acute and rapid reduction of oxidative metabolism. This response may favor a biosynthesis-oriented metabolic program that supports rapid hypertrophic growth.

Cycle exercise training and muscle mass: A preliminary investigation of 17 lower limb muscles in older men

Cycling exercise in older individuals is beneficial for the cardiovascular system and quadriceps muscles, including partially reversing the age-related loss of quadriceps muscle mass. However, the effect of cycling exercise on the numerous other lower limb muscles is unknown. Six older men (74 ± 8 years) underwent MRI before and after 12-weeks of progressive aerobic cycle exercise training (3-4 days/week, 60-180 min/week, 60%-80% heart rate reserve, VO2 max: +13%) for upper (rectus femoris, vastii, adductor longus, adductor magnus, gracilis, sartorius, biceps femoris long head, biceps femoris short head, semimembranosus, semitendinosus) and lower (anterior tibial, posterior tibialis, peroneals, flexor digitorum longus, lateral gastrocnemius, medial gastrocnemius, soleus) leg muscle volumes. In the upper leg, cycle exercise training induced hypertrophy (p ≤ 0.05) in the vastii (+7%) and sartorius (+6%), with a trend to increase biceps femoris short head (+5%, p = 0.1). Additionally, there was a trend to decrease muscle volume in the adductor longus (-6%, p = 0.1) and biceps femoris long head (-5%, p = 0.09). In the lower leg, all 7 muscle volumes assessed were unaltered pre- to post-training (-2% to -3%, p > 0.05). This new evidence related to cycle exercise training in older individuals clarifies the specific upper leg muscles that are highly impacted, while revealing all the lower leg muscles do not appear responsive, in the context of muscle mass and sarcopenia. This study provides information for exercise program development in older individuals, suggesting other specific exercises are needed for the rectus femoris and adductors, certain hamstrings, and the anterior and posterior lower leg muscles to augment the beneficial effects of cycling exercise for older adults.

Effects of tapering on performance in endurance athletes: A systematic review and meta-analysis

OBJECTIVE

To assess the responses to taper in endurance athletes using meta-analysis.

METHODS

Systematic searches were conducted in China National Knowledge Infrastructure, PubMed, Web of Science, SPORTDiscus, and EMBASE databases. Standardized mean difference (SMD) and 95% confidence interval (CI) of outcome measures were calculated as effect sizes.

RESULTS

14 studies were included in this meta-analysis. Significant improvements were found between pre- and post-tapering in time-trial (TT) performance (SMD = -0.45; P < 0.05) and time to exhaustion (TTE) performance (SMD = 1.28; P < 0.05). However, There were no improvements in maximal oxygen consumption ([Formula: see text]) and economy of movement (EM) (P > 0.05) between pre- and post-tapering. Further subgroup analysis showed that tapering combined with pre-taper overload training had a more significant effect on TT performance than conventional tapering (P < 0.05). A tapering strategy that reduced training volume by 41-60%, maintained training intensity and frequency, lasted ≤7 days, 8-14 days, or 15-21 days, used a progressive or step taper could significantly improve TT performance (P < 0.05).

CONCLUSIONS

The tapering applied in conjunction with pre-taper overload training seems to be more conducive to maximize performance gains. Current evidence suggests that a ≤21-day taper, in which training volume is progressively reduced by 41-60% without changing training intensity or frequency, is an effective tapering strategy.

Athletes' Mesenchymal Stem Cells Could Be the Best Choice for Cell Therapy in Omicron-Infected Patients

New severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variant, Omicron, contains 32 mutations that have caused a high incidence of breakthrough infections or re-infections. These mutations have reduced vaccine protection against Omicron and other new emerging variants. This highlights the need to find effective treatment, which is suggested to be stem cell-based therapy. Stem cells could support respiratory epithelial cells and they could restore alveolar bioenergetics. In addition, they can increase the secretion of immunomodulatory cytokines. However, after transplantation, cell survival and growth rate are low because of an inappropriate microenvironment, and stem cells face ischemia, inflammation, and oxidative stress in the transplantation niche which reduces the cells’ survival and growth. Exercise-training can upregulate antioxidant, anti-inflammatory, and anti-apoptotic defense mechanisms and increase growth signaling, thereby improving transplanted cells’ survival and growth. Hence, using athletes’ stem cells may increase stem-cell therapy outcomes in Omicron-affected patients.

State of Knowledge on Molecular Adaptations to Exercise in Humans: Historical Perspectives and Future Directions

For centuries, regular exercise has been acknowledged as a potent stimulus to promote, maintain, and restore healthy functioning of nearly every physiological system of the human body. With advancing understanding of the complexity of human physiology, continually evolving methodological possibilities, and an increasingly dire public health situation, the study of exercise as a preventative or therapeutic treatment has never been more interdisciplinary, or more impactful. During the early stages of the NIH Common Fund Molecular Transducers of Physical Activity Consortium (MoTrPAC) Initiative, the field is well-positioned to build substantially upon the existing understanding of the mechanisms underlying benefits associated with exercise. Thus, we present a comprehensive body of the knowledge detailing the current literature basis surrounding the molecular adaptations to exercise in humans to provide a view of the state of the field at this critical juncture, as well as a resource for scientists bringing external expertise to the field of exercise physiology. In reviewing current literature related to molecular and cellular processes underlying exercise-induced benefits and adaptations, we also draw attention to existing knowledge gaps warranting continued research effort. © 2021 American Physiological Society. Compr Physiol 12:3193-3279, 2022.

The Aging Athlete: Paradigm of Healthy Aging

The Exercise Boom of the 1970's resulted in the adoption of habitual exercise in a significant portion of the population. Many of these individuals are defying the cultural norms by remaining physically active and competing at a high level in their later years. The juxtaposition between masters athletes and non-exercisers demonstrate the importance of remaining physically active throughout the lifespan on physiological systems related to healthspan (years of healthy living). This includes ~50% improved maximal aerobic capacity (VO₂max) and enhanced skeletal muscle health (size, function, as well as metabolic and communicative properties) compared to non-exercisers at a similar age. By taking a reductionist approach to VO₂max and skeletal muscle health, we can gain insight into how aging and habitual exercise affects the aging process. Collectively, this review provides a physiological basis for the elite performances seen in masters athletes, as well as the health implications of lifelong exercise with a focus on VO₂max, skeletal muscle metabolic fitness, whole muscle size and function, single muscle fiber physiology, and communicative properties of skeletal muscle. This review has significant public health implications due to the potent health benefits of habitual exercise across the lifespan.

Characterizing the Tapering Practices of United States and Canadian Raw Powerlifters

ABSTRACT

Travis, SK, Pritchard, HJ, Mujika, I, Gentles, JA, Stone, MH, and Bazyler, CD. Characterizing the tapering practices of United States and Canadian raw powerlifters. J Strength Cond Res 35(12S): S26-S35, 2021-The purpose of this study was to characterize the tapering practices used by North American powerlifters. A total of 364 powerlifters completed a 41-item survey encompassing demographics, general training, general tapering, and specific tapering practices. Nonparametric statistics were used to assess sex (male and female), competition level (regional/provincial, national, and international), and competition lift (squat, bench press, and deadlift). The highest training volume most frequently took place 5-8 weeks before competition, whereas the highest training intensity was completed 2 weeks before competition. A step taper was primarily used over 7-10 days while decreasing the training volume by 41-50% with varied intensity. The final heavy (>85% 1 repetition maximum [1RM]) back squat and deadlift sessions were completed 7-10 days before competition, whereas the final heavy bench press session was completed <7 days before competition. Final heavy lifts were completed at 90.0-92.5% 1RM but reduced to 75-80% 1RM for back squat and bench press and 70-75% for deadlift during the final training session of each lift. Set and repetition schemes during the taper varied between lifts with most frequent reports of 3 × 2, 3 × 3, and 3 × 1 for back squat, bench press, and deadlift, respectively. Training cessation durations before competition varied between deadlift (5.8 ± 2.5 days), back squat (4.1 ± 1.9 days), and bench press (3.9 ± 1.8 days). Complete training cessation was implemented 2.8 ± 1.1 days before competition and varied between sex and competition level. These findings provide novel insights into the tapering practices of North American powerlifters and can be used to inform powerlifting coaches and athlete's tapering decisions.

Skeletal Muscle Adaptations and Performance Outcomes Following a Step and Exponential Taper in Strength Athletes

Before major athletic events, a taper is often prescribed to facilitate recovery and enhance performance. However, it is unknown which taper model is most effective for peaking maximal strength and positively augmenting skeletal muscle. Thus, the purpose of this study was to compare performance outcomes and skeletal muscle adaptations following a step vs. an exponential taper in strength athletes. Sixteen powerlifters (24.0 ± 4.0 years, 174.4 ± 8.2 cm, 89.8 ± 21.4 kg) participated in a 6-week training program aimed at peaking maximal strength on back squat [initial 1-repetition-maximum (1RM): 174.7 ± 33.4 kg], bench press (118.5 ± 29.9 kg), and deadlift (189.9 ± 41.2 kg). Powerlifters were matched based on relative maximal strength, and randomly assigned to either (a) 1-week overreach and 1-week step taper or (b) 1-week overreach and 3-week exponential taper. Athletes were tested pre- and post-training on measures of body composition, jumping performance, isometric squat, and 1RM. Whole muscle size was assessed at the proximal, middle, and distal vastus lateralis using ultrasonography and microbiopsies at the middle vastus lateralis site. Muscle samples (n = 15) were analyzed for fiber size, fiber type [myosin-heavy chain (MHC)-I, -IIA, -IIX, hybrid-I/IIA] using whole muscle immunohistochemistry and single fiber dot blots, gene expression, and microRNA abundance. There were significant main time effects for 1RM squat (p < 0.001), bench press (p < 0.001), and deadlift, (p = 0.024), powerlifting total (p < 0.001), Wilks Score (p < 0.001), squat jump peak-power scaled to body mass (p = 0.001), body mass (p = 0.005), fat mass (p = 0.002), and fat mass index (p = 0.002). There were significant main time effects for medial whole muscle cross-sectional area (mCSA) (p = 0.006) and averaged sites (p < 0.001). There was also a significant interaction for MHC-IIA fiber cross-sectional area (fCSA) (p = 0.014) with post hoc comparisons revealing increases following the step-taper only (p = 0.002). There were significant main time effects for single-fiber MHC-I% (p = 0.015) and MHC-IIA% (p = 0.033), as well as for MyoD (p = 0.002), MyoG (p = 0.037), and miR-499a (p = 0.033). Overall, increases in whole mCSA, fCSA, MHC-IIA fCSA, and MHC transitions appeared to favor the step taper group. An overreach followed by a step taper appears to produce a myocellular environment that enhances skeletal muscle adaptations, whereas an exponential taper may favor neuromuscular performance.

Longer Disciplined Tapers Improve Marathon Performance for Recreational Runners

For marathoners the taper refers to a period of reduced training load in the weeks before race-day. It helps runners to recover from the stresses of weeks of high-volume, high-intensity training to enhance race-day performance. The aim of this study was to analyse the taper strategies of recreational runners to determine whether particular forms of taper were more or less favorable to race-day performance.

Methods: We analyzed the training activities of more than 158,000 recreational marathon runners to define tapers based on a decrease in training volume (weekly distance). We identified different types of taper based on a combination of duration (1–4 weeks of decreasing training) and discipline (strict tapers progressively decrease training in the weeks before the marathon, relaxed tapers do not) and we grouped runners based on their taper type to determine the popularity of different types of taper and their associated performance characteristics.

Results: Kruskal-Wallis tests (H(7)≥ 521.11, p < 0.001), followed by posthoc Dunns tests with a Bonferroni correction, confirmed that strict tapers were associated with better marathon performance than relaxed tapers (p < 0.001) and that longer tapers of up to 3 weeks were associated with better performance than shorter tapers (p < 0.001). Results indicated that strict 3-week tapers were associated with superior marathon finish-time benefits (a median finish-time saving of 5 min 32.4 s or 2.6%) compared with a minimal taper (p < 0.001). We further found that female runners were associated with greater finish-time benefits than men, for a given taper type ( ≤ 3-weeks in duration), based on Mann Whitney U tests of significance with p < 0.001.

Conclusion: The findings of this study for recreational runners are consistent with related studies on highly-trained athletes, where disciplined tapers were associated with comparable performance benefits. The findings also highlight how most recreational runners (64%) adopt less disciplined (2-week and 3-week) tapers and suggest that shifting to a more disciplined taper strategy could improve performance relative to the benefits of a less disciplined taper.

Human adipose and skeletal muscle tissue DNA, RNA, and protein content

The purpose of this project was to provide a profile of DNA, RNA, and protein content in adipose tissue, which is relatively understudied in humans, to gain more insight into the amount of tissue that may be required for various analyses. Skeletal muscle tissue was also investigated to provide a direct comparison into potential differences between these two highly metabolically active tissues. Basal adipose and skeletal muscle tissue samples were obtained from 10 (7 M, 3 W) recreationally active participants [25 ± 1 yr; 84 ± 3 kg, maximal oxygen consumption (V̇o_2max): 3.5 ± 0.2 L/min, body fat: 29 ± 2%]. DNA, RNA, and protein were extracted and subsequently analyzed for quantity and quality. DNA content of adipose and skeletal muscle tissue was 52 ± 14 and 189 ± 44 ng DNA·mg tissue^-1, respectively (P < 0.05). RNA content of adipose and skeletal muscle tissue was 46 ± 14 and 537 ± 72 ng RNA·mg tissue^-1, respectively (P < 0.05). Protein content of adipose and skeletal muscle tissue was 4 ± 1 and 177 ± 10 µg protein·mg tissue^-1, respectively (P < 0.05). In summary, human adipose had 28% of the DNA, 9% of the RNA, and 2% of the protein found in skeletal muscle per mg of tissue. This information should be useful across a wide range of human clinical investigation designs and various laboratory analyses.NEW & NOTEWORTHY This investigation studied DNA, RNA, and protein contents of adipose and skeletal muscle tissues from young active individuals. A series of optimization steps were investigated to aid in determining the optimal approach to extract high-yield and high-quality biomolecules. These findings contribute to the knowledge gap in adipose tissue requirements for molecular biology assays, which is of increasing importance due to the growing interest in adipose tissue research involving human exercise physiology research.

Single muscle fibre contractile characteristics with lifelong endurance exercise

KEY POINTS

A hallmark trait of ageing skeletal muscle health is a reduction in size and function, which is most pronounced in the fast muscle fibres. We studied older men (74 ± 4 years) with a history of lifelong (>50 years) endurance exercise to examine potential benefits for slow and fast muscle fibre size and contractile function. Lifelong endurance exercisers had slow muscle fibres that were larger, stronger, faster and more powerful than young exercisers (25 ± 1 years) and age-matched non-exercisers (75 ± 2 years). Limited benefits with lifelong endurance exercise were noted in the fast muscle fibres. These findings suggest that additional exercise modalities (e.g. resistance exercise) or other therapeutic interventions are needed to target fast muscle fibres with age.

ABSTRACT

We investigated single muscle fibre size and contractile function among three groups of men: lifelong exercisers (LLE) (n = 21, 74 ± 4 years), old healthy non-exercisers (OH) (n = 10, 75 ± 2 years) and young exercisers (YE) (n = 10, 25 ± 1 years). On average, LLE had exercised ∼5 days week^-1 for ∼7 h week^-1 over the past 53 ± 6 years. LLE were subdivided based on lifelong exercise intensity into performance (LLE-P) (n = 14) and fitness (LLE-F) (n = 7). Muscle biopsies (vastus lateralis) were examined for myosin heavy chain (MHC) slow (MHC I) and fast (MHC IIa) fibre size and function (strength, speed, power). LLE MHC I size (7624 ± 2765 μm² ) was 25-40% larger (P < 0.001) than YE (6106 ± 1710 μm² ) and OH (5476 ± 2467 μm² ). LLE MHC I fibres were ∼20% stronger, ∼10% faster and ∼30% more powerful than YE and OH (P < 0.05). By contrast, LLE MHC IIa size (6466 ± 2659 μm² ) was similar to OH (6237 ± 2525 μm² ; P = 0.854), with both groups ∼20% smaller (P < 0.001) than YE (7860 ± 1930 μm² ). MHC IIa contractile function was variable across groups, with a hierarchical pattern (OH > LLE > YE; P < 0.05) in normalized power among OH (16.7 ± 6.4 W L^-1 ), LLE (13.9 ± 4.5 W L^-1 ) and YE (12.4 ± 3.5 W L^-1 ). The LLE-P and LLE-F had similar single fibre profiles with MHC I power driven by speed (LLE-P) or force (LLE-F), suggesting exercise intensity impacted slow muscle fibre mechanics. These data suggest that lifelong endurance exercise benefited slow muscle fibre size and function. Comparable fast fibre characteristics between LLE and OH, regardless of training intensity, suggest other exercise modes (e.g. resistance training) or myotherapeutics may be necessary to preserve fast muscle fibre size and performance with age.

Muscle fiber typology is associated with the incidence of overreaching in response to overload training

Variability in the performance responses following an overload training period and subsequent taper was associated with the variation in the muscle fiber typology of the gastrocnemius. Runners with an estimated higher proportion of type I fibers (i.e., lower carnosine z-score) were able to maintain performance in response to an overload training period and subsequently achieve a superior performance supercompensation. These findings show that muscle fiber typology contributes to the variability in performance responses following training.

Fiber typing human skeletal muscle with fluorescent immunohistochemistry

Skeletal muscle myosin heavy chain (MyHC) fiber type composition is a critical determinant of overall muscle function and health. Various approaches interrogate fiber type at the single cell, but the two most commonly utilized are single-muscle fiber sodium dodecyl sulfate-polyacrylamide gel electrophoresis (smfSDS-PAGE) and fluorescent immunohistochemistry (IHC). Although smfSDS-PAGE is generally considered the "gold standard," IHC is more commonly used because of its time-effectiveness and relative ease. Unfortunately, there is lingering inconsistency on how best to accurately and quickly determine fiber type via IHC and an overall misunderstanding regarding pure fiber type proportions, specifically the abundance of fibers exclusively expressing highly glycolytic MyHC IIX in humans. We therefore 1) present information and data showing the low abundance of pure MyHC IIX muscle fibers in healthy human skeletal muscle and 2) leverage this information to provide straightforward protocols that are informed by human biology and employ inexpensive, easily attainable antibodies for the accurate determination of fiber type.

Skeletal Muscle Fiber Adaptations Following Resistance Training Using Repetition Maximums or Relative Intensity

The purpose of the study was to compare the physiological responses of skeletal muscle to a resistance training (RT) program using repetition maximum (RM) or relative intensity (RI_SR). Fifteen well-trained males underwent RT 3 d·wk⁻¹ for 10 weeks in either an RM group (n = 8) or RI_SR group (n = 7). The RM group achieved a relative maximum each day, while the RI_SR group trained based on percentages. The RM group exercised until muscular failure on each exercise, while the RI_SR group did not reach muscular failure throughout the intervention. Percutaneous needle biopsies of the vastus lateralis were obtained pre-post the training intervention, along with ultrasonography measures. Dependent variables were: Fiber type-specific cross-sectional area (CSA); anatomical CSA (ACSA); muscle thickness (MT); mammalian target of rapamycin (mTOR); adenosine monophosphate protein kinase (AMPK); and myosin heavy chains (MHC) specific for type I (MHC1), type IIA (MHC2A), and type IIX (MHC2X). Mixed-design analysis of variance and effect size using Hedge’s g were used to assess within- and between-group alterations. RI_SR statistically increased type I CSA (p = 0.018, g = 0.56), type II CSA (p = 0.012, g = 0.81), ACSA (p = 0.002, g = 0.53), and MT (p < 0.001, g = 1.47). RI_SR also yielded a significant mTOR reduction (p = 0.031, g = −1.40). Conversely, RM statistically increased only MT (p = 0.003, g = 0.80). Between-group effect sizes supported RI_SR for type I CSA (g = 0.48), type II CSA (g = 0.50), ACSA (g = 1.03), MT (g = 0.72), MHC2X (g = 0.31), MHC2A (g = 0.87), and MHC1 (g = 0.59); with all other effects being of trivial magnitude (g < 0.20). Our results demonstrated greater adaptations in fiber size, whole-muscle size, and several key contractile proteins when using RI_SR compared to RM loading paradigms.

Phase-Specific Changes in Rate of Force Development and Muscle Morphology Throughout a Block Periodized Training Cycle in Weightlifters

The purpose of this study was to investigate the kinetic and morphological adaptations that occur during distinct phases of a block periodized training cycle in weightlifters. Athlete monitoring data from nine experienced collegiate weightlifters was used. Isometric mid-thigh pull (IMTP) and ultrasonography (US) results were compared to examine the effects of three specific phases of a training cycle leading up to a competition. During the high volume strength-endurance phase (SE) small depressions in rate of force development (RFD) but statistically significant (p ≤ 0.05) increases in vastus lateralis cross-sectional area (CSA), and body mass (BM) were observed. The lower volume higher intensity strength-power phase (SP) caused RFD to rebound above pre-training cycle values despite statistically significant reductions in CSA. Small to moderate increases only in the earlier RFD time bands (<150 ms) occurred during the peak/taper phase (PT) while CSA and BM were maintained. Changes in IMTP RFD and CSA from US reflected the expected adaptations of block periodized training phases. Changes in early (<100 ms) and late (≥150 ms) RFD time bands may not occur proportionally throughout different training phases. Small increases in RFD and CSA can be expected in well-trained weightlifters throughout a single block periodized training cycle.

Effects of an increase in intensity during tapering on 1500-m running performance

We examined the effect of completing the final interval training session during a taper at either (i) race pace (RP) or (ii) faster than RP on 1500-m running performance and neuromuscular performance. Ten trained runners (age, 21.7 ± 3.0 years; height, 182.9 ± 7.0 cm; body mass, 73.4 ± 6.8 kg; and personal best 1500-m time, 4:17.5 ± 0:26.9 min) completed 2 conditions consisting of 7 days of regular training and a 7-day taper, separated by 3 weeks of training. In 1 condition, the taper was prescribed using prediction models based on the practices of elite British middle-distance runners, with the intensity of the final interval session being equal to 1500-m RP. The taper was repeated in the high-intensity (HI) condition, with the exception that the final interval session was completed at 115% of 1500-m RP. A 1500-m treadmill time trial and measures of maximal voluntary contraction (MVC) and rate of force development (RFD) were completed before and after regular training and tapering. Performance was most likely improved after RP (mean ± 90% confidence limits, 10.1 ± 1.6 s), and possibly beneficial after HI (4.2 ± 12.0 s). Both MVC force (p = 0.002) and RFD (p = 0.02) were improved after tapering, without differences between conditions. An RP taper based on the practices of elite middle-distance runners is recommended to improve performance in young, subelite runners. The effect of this strategy with an increase in interval intensity is highly variable and should be implemented with caution.

Protein Supplementation Throughout 10 Weeks of Progressive Run Training Is Not Beneficial for Time Trial Improvement

Introduction: Protein supplementation is proposed to promote recovery and adaptation following endurance exercise. While prior literature demonstrates improved performance when supplementing protein during or following endurance exercise, chronic supplementation research is limited.

Methods: Runners (VO₂peak = 53.6 ± 8.9 ml/kg/min) were counter-balanced into a placebo group (PLA; n = 8) or protein group (PRO; n = 9) based on sex and VO₂peak, and underwent 10 weeks of progressive endurance training. Prior to training, body composition, blood cell differentials, non-invasive mitochondrial capacity using near-infrared spectroscopy, and a 5 km treadmill time trial (TT) were evaluated. Progressive training then commenced (5–10% increase in weekly volume with a recovery week following 3 weeks of training) whereby PRO supplemented with 25 g of whey protein following workouts and prior to sleep (additional 50 g daily). PLA supplemented similarly with a < 1 g sugar pill per day. Following training, participants were reanalyzed for the aforementioned tests.

Results: VO₂peak and initial 5 km TT were not significantly different between groups. PRO consumed significantly more dietary protein throughout the training period (PRO = 132 g/d or 2.1 g/kg/day; PLA = 84 g/d or 1.2 g/kg/day). Running volume increased significantly over time, but was not significantly different between groups throughout training. Blood measures were unaltered with training or supplementation. Mitochondrial capacity trended toward improving over time (time p = 0.063) with no difference between groups. PLA increased lean mass 0.7 kg (p < 0.05) while PRO experienced infinitesimal change (−0.1 kg, interaction p = 0.049). PLA improved 5 km TT performance 6.4% (1 min 31 s), while PRO improved only 2.7% (40 s) (interaction p = 0.080).

Conclusion: This is the first evidence to suggest long-term protein supplementation during progressive run training is not beneficial for runners.

Effect of aerobic training on baseline expression of signaling and respiratory proteins in human skeletal muscle

Most studies examining the molecular mechanisms underlying adaptation of human skeletal muscles to aerobic exercise focused on the response to acute exercise. Here, we examined the effect of a 2-month aerobic training program on baseline parameters in human muscle. Ten untrained males performed a one-legged knee extension exercise for 1 h with the same relative intensity before and after a 2-month aerobic training program. Biopsy samples were taken from vastus lateralis muscle at rest before and after the 2 month training program (baseline samples). Additionally, biopsy samples were taken from the exercised leg 1 and 4 h after the one-legged continuous knee extension exercise. Aerobic training decreases baseline phosphorylation of FOXO1Ser256 , increases that of CaMKIIThr286 , CREB1Ser133 , increases baseline expression of mitochondrial proteins in respiratory complexes I-V, and some regulators of mitochondrial biogenesis (TFAM, NR4A3, and CRTC2). An increase in the baseline content of these proteins was not associated with a change in baseline expression of their genes. The increase in the baseline content of regulators of mitochondrial biogenesis (TFAM and NR4A3) was associated with a transient increase in transcription after acute exercise. Contrariwise, the increase in the baseline content of respiratory proteins does not seem to be regulated at the transcriptional level; rather, it is associated with other mechanisms. Adaptation of human skeletal muscle to regular aerobic exercise is associated not only with transient molecular responses to exercise, but also with changes in baseline phosphorylation and expression of regulatory proteins.

Jumping Performance is Preserved but Not Muscle Thickness in Collegiate Volleyball Players After a Taper

Bazyler, CD, Mizuguchi, S, Sole, CJ, Suchomel, TJ, Sato, K, Kavanaugh, AA, DeWeese, BH, and Stone, MH. Jumping performance is preserved but not muscle thickness in collegiate volleyball players after a taper. J Strength Cond Res 32(4): 1020-1028, 2018-The purpose of this study was to examine changes in muscle architecture and jumping performance in NCAA division I women's volleyball players throughout a competitive season and in preparation for conference championships. Ten women volleyball players were tested at preseason (T1), pretaper (T2), and post-taper (T3) on measures of vastus lateralis muscle thickness (MT), pennation angle (PA) and fascicle length (FL) using ultrasonography, and unloaded and loaded squat jump height (SJH) and peak power allometrically scaled to body mass (SJPPa) on a force platform. Rating of perceived exertion training load and strength training volume load were monitored weekly. Player's MT (p < 0.001, Glass's Δ = 2.8) and PA increased (p = 0.02, Δ = 3.9) after in-season training. However, MT decreased after the taper (p = 0.01, Δ = 0.6) but remained elevated above preseason values (p < 0.001, Δ = 1.7). There were no statistical changes in FL, SJH, or SJPPa. Large-to-very large negative relationships (r = -0.51 to -0.81) were observed between preseason relative maximal strength and changes in SJH and SJPPa with various loads over the season. These findings demonstrate that relatively low volumes of strength training and concurrent sport training during a tapering period are capable of preserving jumping performance, but not MT in women's volleyball players; however, jumping performance changes seem to be related to the player's strength level. Stronger players may benefit from an overreaching microcycle before the taper to preserve previously accrued muscular adaptations and jumping performance.

Myonuclear Domain Flexibility Challenges Rigid Assumptions on Satellite Cell Contribution to Skeletal Muscle Fiber Hypertrophy

Satellite cell-mediated myonuclear accretion is thought to be required for skeletal muscle fiber hypertrophy, and even drive hypertrophy by preceding growth. Recent studies in humans and rodents provide evidence that challenge this axiom. Specifically, Type 2 muscle fibers reliably demonstrate a substantial capacity to hypertrophy in the absence of myonuclear accretion, challenging the notion of a tightly regulated myonuclear domain (i.e., area that each myonucleus transcriptionally governs). In fact, a “myonuclear domain ceiling”, or upper limit of transcriptional output per nucleus to support hypertrophy, has yet to be identified. Satellite cells respond to muscle damage, and also play an important role in extracellular matrix remodeling during loading-induced hypertrophy. We postulate that robust satellite cell activation and proliferation in response to mechanical loading is largely for these purposes. Future work will aim to elucidate the mechanisms by which Type 2 fibers can hypertrophy without additional myonuclei, the extent to which Type 1 fibers can grow without myonuclear accretion, and whether a true myonuclear domain ceiling exists.

Changes in Muscle Architecture, Explosive Ability, and Track and Field Throwing Performance Throughout a Competitive Season and After a Taper

The purpose of this study was to examine the effects of an overreach and taper on measures of muscle architecture, jumping, and throwing performance in Division I collegiate throwers preparing for conference championships. Six collegiate track and field throwers (3 hammer, 2 discus, 1 javelin) trained for 12 weeks using a block-periodization model culminating with a 1-week overreach followed by a 3-week taper (ORT). Session rating of perceived exertion training load (RPETL) and strength training volume-load times bar displacement (VLd) were recorded weekly. Athletes were tested pre-ORT and post-ORT on measures of vastus lateralis architecture, unloaded and loaded squat and countermovement jump performance, underhand and overhead throwing performance, and competition throwing performance. There was a statistical reduction in weight training VLd/session (d = 1.21, p ≤ 0.05) and RPETL/session (d = 0.9, p ≤ 0.05) between the in-season and ORT training phases. Five of 6 athletes improved overhead throw and competition throwing performance after the ORT (d = 0.50, p ≤ 0.05). Vastus lateralis muscle thickness statistically increased after the in-season training phase (d = 0.28, p ≤ 0.05) but did not change after the ORT. Unloaded countermovement jump peak force and relative peak power improved significantly after the ORT (d = 0.59, p ≤ 0.05, d = 0.31, p ≤ 0.05, respectively). These findings demonstrate that an overreaching week followed by a 3-week taper is an effective means of improving explosive ability and throwing performance in collegiate track and field throwers despite the absence of detectable changes in muscle architecture.

Effect of tapering after a period of high-volume sprint interval training on running performance and muscular adaptations in moderately trained runners

The effect of tapering following a period of high-volume sprint interval training (SIT) and a basic volume of aerobic training on performance and muscle adaptations in moderately trained runners was examined. Eleven (8 men, 3 women) runners [maximum oxygen uptake (V̇o2max): 56.8 ± 2.9 ml·min−1·kg−1; mean ± SD] conducted high-volume SIT (HV; 20 SIT sessions; 8–12 × 30 s all-out) for 40 days followed by 18 days of tapering (TAP; 4 SIT sessions; 4 × 30 s all-out). Before and after HV as well as midway through and at the end of TAP, the subjects completed a 10-km running test and a repeated running test at 90% of vV̇o2max to exhaustion (RRT). In addition, a biopsy from the vastus lateralis muscle was obtained at rest. Performance during RRT was better ( P < 0.01) at the end of TAP than before HV (6.8 ± 0.5 vs. 5.6 ± 0.5 min; means ± SE), and 10-km performance was 2.7% better ( P < 0.05) midway through (40.7 ± 0.7 min) and at the end of (40.7 ± 0.6 min) TAP than after HV (41.8 ± 0.9 min). The expression of muscle Na+-K+-ATPase (NKA)α1, NKAβ1, phospholemman (FXYD1), and sarcoplasmic reticulum calcium transport ATPase (SERCA1) increased ( P < 0.05) during HV and remained higher during TAP. In addition, oxygen uptake at 60% of vV̇o2max was lower ( P < 0.05) at the end of TAP than before and after HV. Thus short-duration exercise capacity and running economy were better than before the HV period together with higher expression of muscle proteins related to Na+/K+ transport and Ca2+ reuptake, while 10-km performance was not significantly improved by the combination of HV and tapering.

NEW & NOTEWORTHY Short-duration performance became better after 18 days of tapering from ~6 wk of high-volume sprint interval training (SIT), whereas 10-km performance was not significantly affected by the combination of high-volume SIT and tapering. Higher expression of muscle NKAα1, NKAβ1, FXYD1, and SERCA1 may reflect faster Na+/K+ transport and Ca2+ reuptake that could explain the better short-duration performance. These results suggest that the type of competition should determine the duration of tapering to optimize performance.

Branched-chain amino acids administration suppresses endurance exercise-related activation of ubiquitin proteasome signaling in trained human skeletal muscle

We tested whether post exercise ingestion of branched-chain amino acids (BCAA < 10 g) is sufficient to activate signaling associated with muscle protein synthesis and suppress exercise-induced activation of mechanisms associated with proteolysis in endurance-trained human skeletal muscle. Nine endurance-trained athletes performed a cycling bout with and without BCAA ingestion (0.1 g/kg). Post exercise ACCSer79/222 phosphorylation (endogenous marker of AMPK activity) was increased (~3-fold, P < 0.05) in both sessions. No changes were observed in IGF1 mRNA isoform expression or phosphorylation of the key anabolic markers - p70S6K1Thr389 and eEF2Thr56 - between the sessions. BCAA administration suppressed exercise-induced expression of mTORC1 inhibitor DDIT4 mRNA, eliminated activation of the ubiquitin proteasome system, detected in the control session as decreased FOXO1Ser256 phosphorylation (0.83-fold change, P < 0.05) and increased TRIM63 (MURF1) expression (2.4-fold, P < 0.05). Therefore, in endurance-trained human skeletal muscle, post exercise BCAA ingestion partially suppresses exercise-induced expression of PGC-1a mRNA, activation of ubiquitin proteasome signaling, and suppresses DDIT4 mRNA expression.

Thyroid hormones and commonly cited symptoms of overtraining in collegiate female endurance runners

PURPOSE

Overtraining syndrome (OTS) is reported in endurance sports. Thyroid hormones (TH) regulate metabolism, mood, and energy production, and may play a role in OTS of endurance athletes. The purpose of this study was to investigate relationships in TH and symptoms of OTS in track and field endurance runners (ER).

METHODS

Sixteen female track and field middle distance (MD; n = 9; age: 20.2 ± 1.5 years; ht: 167.86 ± 5.04 cm; body-mass: 57.97 ± 5.05 kg; VO_2MAX: 53.62 ± 6.04 ml/kg/min) and long distance (LD; n = 7; age: 20.5 ± 1.5 years; ht: 162.48 ± 6.11 cm; body-mass: 56.15 ± 5.99 kg; VO_2MAX: 61.94 ± 3.29 ml/kg/min) ER participated in this descriptive study (15-weeks). Thyroid-stimulating hormone (TSH), triiodothyronine (T ₃), and thyroxine (T ₄), were collected at pre-(PRE) and post-season (POST). A fatigue scale was administered weekly, and percent change (PΔ) in race time (season best vs. championship performance) was calculated. Wilcoxon-sign ranked tests and Spearman's rho correlations were used to determine changes and relationships between TH and performance.

RESULTS

TSH, T ₃ and T ₄ did not change from PRE to POST. The percent change (PΔ) in T ₃ from PRE to POST was correlated with running performance at the end of the season (ρ = - 0.70, p = 0.036). Fatigue at week 12 correlated with running performance at the end of the season (ρ = - 0.74, p = 0.004).

CONCLUSION

TH may be valuable in assessing the overall training state of ER. TH concentrations change too slowly to be a frequent marker of monitoring OTS, but are related to markers of decreased performance. Monitoring dietary intake, and fatigue may be predictive markers to assess OTS and training status of female ER.

Fiber Type-Specific Satellite Cell Content in Cyclists Following Heavy Training with Carbohydrate and Carbohydrate-Protein Supplementation

The central purpose of this study was to evaluate the fiber type-specific satellite cell and myonuclear responses of endurance-trained cyclists to a block of intensified training, when supplementing with carbohydrate (CHO) vs. carbohydrate-protein (PRO). In a crossover design, endurance-trained cyclists (n = 8) performed two consecutive training periods, once supplementing with CHO (de facto “control” condition) and the other with PRO. Each training period consisted of 10 days of intensified cycle training (ICT–120% increase in average training duration) followed by 10 days of recovery (RVT–reduced volume training; 33% volume reduction vs. normal training). Skeletal muscle biopsies were obtained from the vastus lateralis before and after ICT and again following RVT. Immunofluorescent microscopy was used to quantify SCs (Pax7+), myonuclei (DAPI+), and myosin heavy chain I (MyHC I). Data are expressed as percent change ± 90% confidence limits. The 10-day block of ICT_CHO increased MyHC I SC content (35 ± 28%) and myonuclear density (16 ± 6%), which remained elevated following RVT_CHO (SC = 69 ± 50% vs. PRE; Nuclei = 17 ± 15% vs. PRE). MyHC II SC and myonuclei were not different following ICT_CHO, but were higher following RVT_CHO (SC = +33 ± 31% vs. PRE; Nuclei = 15 ± 14% vs. PRE), indicating a delayed response compared to MyHC I fibers. The MyHC I SC pool increased following ICT_PRO (37 ± 37%), but without a concomitant increase in myonuclei. There were no changes in MyHC II SC or myonuclei following ICT_PRO. Collectively, these trained endurance cyclists possessed a relatively large pool of SCs that facilitated rapid (MyHC I) and delayed (MyHC II) satellite cell proliferation and myonuclear accretion under carbohydrate conditions. The current findings strengthen the growing body of evidence demonstrating alterations in satellite cell number in the absence of hypertrophy. Satellite cell pool expansion is typically viewed as an advantageous response to exercise. However, when coupled with our previous report that PRO possibly enhanced whole muscle recovery and increased MyHC I and II fiber size, the limited satellite cell/myonuclear response observed with carbohydrate-protein seem to indicate that protein supplementation may have minimized the necessity for satellite cell involvement, thereby suggesting that protein may benefit skeletal muscle during periods of heavy training.

Heat shock proteins and exercise adaptations. Our knowledge thus far and the road still ahead

By its very nature, exercise exerts a challenge to the body's cellular homeostatic mechanisms. This homeostatic challenge affects not only the contracting skeletal muscle but also a number of other organs and results over time in exercise-induced adaptations. Thus it is no surprise that heat shock proteins (HSPs), a group of ancient and highly conserved cytoprotective proteins critical in the maintenance of protein and cellular homeostasis, have been implicated in exercise/activity-induced adaptations. It has become evident that HSPs such as HSP72 are induced or activated with acute exercise or after chronic exercise training regimens. These observations have given scientists an insight into the protective mechanisms of these proteins and provided an opportunity to exploit their protective role to improve health and physical performance. Although our knowledge in this area of physiology has improved dramatically, many questions still remain unanswered. Further understanding of the role of HSPs in exercise physiology may prove beneficial for therapeutic targeting in diseased patient cohorts, exercise prescription for disease prevention, and training strategies for elite athletes.

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.

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 (n = 6, 20±1 y, VO_2max = 70±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% HR_max) 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.

Tapering strategies in elite British endurance runners

The aim of the study was to explore pre-competition training practices of elite endurance runners. Training details from elite British middle distance (MD; 800 m and 1500 m), long distance (LD; 3000 m steeplechase to 10,000 m) and marathon (MAR) runners were collected by survey for 7 days in a regular training (RT) phase and throughout a pre-competition taper. Taper duration was [median (interquartile range)] 6 (3) days in MD, 6 (1) days in LD and 14 (8) days in MAR runners. Continuous running volume was reduced to 70 (16)%, 71 (24)% and 53 (12)% of regular levels in MD, LD and MAR runners, respectively (P < 0.05). Interval running volume was reduced compared to regular training (MD; 53 (45)%, LD; 67 (23)%, MAR; 64 (34)%, P < 0.05). During tapering, the peak interval training intensity was above race speed in LD and MAR runners (112 (27)% and 114 (3)%, respectively, P < 0.05), but not different in MD (100 (2)%). Higher weekly continuous running volume and frequency in RT were associated with greater corresponding reductions during the taper (R = -0.70 and R = -0.63, respectively, both P < 0.05). Running intensity during RT was positively associated with taper running intensity (continuous intensity; R = 0.97 and interval intensity; R = 0.81, both P < 0.05). Algorithms were generated to predict and potentially prescribe taper content based on the RT of elite runners. In conclusion, training undertaken prior to the taper in elite endurance runners is predictive of the tapering strategy implemented before competition.

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 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 ± 3 kg) 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 VO(2max) ∼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 V(o) (-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 42.2 km of continuous running - further strengthening the existing body of evidence for skeletal muscle specificity.