NASA SPRINT exercise program efficacy for vastus lateralis and soleus skeletal muscle health during 70 days of simulated microgravity.

The efficacy of the NASA SPRINT exercise countermeasures program for quadriceps (vastus lateralis) and triceps surae (soleus) skeletal muscle health was investigated during 70 days of simulated microgravity. Individuals completed 6° head-down-tilt bedrest (BR, n=9), bedrest with resistance and aerobic exercise (BRE, n=9), or bedrest with resistance and aerobic exercise and low-dose testosterone (BRE+T, n=8). All groups were periodically tested for muscle (n=9 times) and aerobic (n=4 times) power during bedrest. In BR, surprisingly, the typical bedrest-induced decrements in vastus lateralis myofiber size and power were either blunted (MHC I) or eliminated (MHC IIa), along with no change (P>0.05) in %MHC distribution and blunted quadriceps atrophy. In BRE, MHC I (vastus lateralis and soleus) and IIa (vastus lateralis) contractile performance was maintained (P>0.05) or increased (P<0.05). Vastus lateralis hybrid fiber percentage was reduced (P<0.05) and energy metabolism enzymes and capillarization were generally maintained (P>0.05), while not all of these positive responses were observed in the soleus. Exercise offset 100% of quadriceps and ~ ⅔ of soleus whole muscle mass loss. Testosterone (BRE+T) did not provide any benefit over exercise alone for either muscle, and for some myocellular parameters appeared detrimental. In summary, the periodic testing likely provided a partial exercise countermeasure for the quadriceps in the bedrest group, which is a novel finding given the extremely low exercise dose. The SPRINT exercise program appears to be viable for the quadriceps; however, refinement is needed to completely protect triceps surae myocellular and whole muscle health for astronauts on long-duration spaceflights.

Effects of aging and lifelong aerobic exercise on expression of innate immune components in skeletal muscle of women.

This study examined the effects of aging and lifelong aerobic exercise on innate immune system components in the skeletal muscle of healthy women in the basal state and after an unaccustomed resistance exercise (RE) challenge. We also made exploratory between-sex comparisons with our previous report on men. Three groups of women were studied: young exercisers (YE, n = 10, 25 ± 1 yr, V̇o2max: 44 ± 2 mL/kg/min), lifelong aerobic exercisers with a 48 ± 2 yr training history (LLE, n = 7, 72 ± 2 yr, V̇o2max: 26 ± 2 mL/kg/min), and old healthy nonexercisers (OH, n = 10, 75 ± 1 yr, V̇o2max: 18 ± 1 mL/kg/min). Ten Toll-like receptors (TLRs)1-10, TLR adaptors (Myd88, TRIF), and NF-κB pathway components (IκBα, IKKß) were assessed at the mRNA level in vastus lateralis biopsies before and 4 h after RE [3×10 repetitions, 70% 1-repetition maximum (1RM)]. Basal TLR1-10 expression was minimally influenced by age or LLE in women (TLR9 only; OH > YE, +43%, P < 0.05; OH > LLE, +30%, P < 0.10) and was on average 24% higher in women versus men. Similarly, basal adaptor expression was not influenced (P > 0.05) by age or LLE in women but was on average 26% higher (myeloid differentiation primary response 88, Myd88) and 23% lower [Toll interleukin (IL)-1 receptor-containing adaptor-inducing interferon-γ, TRIF] in women versus men. RE-induced changes in women, independent of the group, in TLR3, TLR4, TLR6 (∼2.1-fold, P < 0.05), Myd88 (∼1.2-fold, P < 0.10), and IκBα (∼0.3-fold, P < 0.05). Although there were some similar RE responses in men (TLR4: 2.1-fold, Myd88: 1.2-fold, IκBα: 0.4-fold), several components responded only in men to RE (TLR1, TLR8, TRIF, and IKKß). Our findings support the sexual dimorphism of immunity, with women having greater basal skeletal muscle TLR expression and differential response to unaccustomed exercise than men.NEW & NOTEWORTHY We recently reported that aging increases basal expression of many Toll-like receptors (TLRs) in men and lifelong aerobic exercise does not prevent this effect. In addition, a resistance exercise (RE) challenge increased the expression of many TLRs. Here we show that basal TLR expression is minimally influenced by aging in women and findings support the sexual dimorphism of immunity, with women having greater basal skeletal muscle TLR expression and a differential response to unaccustomed exercise than men.

Adipose biopsy techniques for studies in human exercise physiology.

Adipose biopsy techniques are relatively undefined for exercise physiology research in individuals at or near normal weight. The purpose of this study was to compare the influence of two adipose biopsy techniques on tissue quality through measurements of adipocyte cell size, as well as mRNA and protein levels of select pro- and anti-inflammatory cytokines and adipokines. Thirteen participants (9 M, 4 W; 28 ± 4 yr; 27 ± 3 kg·m-2; V̇o2max: 3.3 ± 0.7 L·min-1) underwent subcutaneous adipose biopsies on either side of the umbilicus (incision: ∼8 cm lateral, sampling area: ∼5 cm lateral) using 1) a 6-mm Bergström biopsy needle and 2) a mini-liposuction approach with a 4-mm Mercedes biopsy needle that used prebiopsy tumescent delivery (∼30 mL 0.9% NaCl solution) into the sampling area (i.e., 'wet' technique). Tissue obtained was processed identically for analysis and both techniques returned high-quality tissue for histology (similar % intact adipocytes), mRNA (RNA integrity numbers >7.0), and protein. Adipocyte size was similar (P > 0.05) between both techniques (Bergström: 6,116 ± 1,652 µm2, 554-23,522 µm2; Mercedes: 6,517 ± 952 µm2, 926-21,969 µm2). There were also no differences (P > 0.05) between the two techniques for the measured cytokines (pro- and anti-inflammatory) and adipokines at the mRNA and protein levels. Adipocyte size was positively correlated with body mass index and body fat percentage, and negatively correlated with V̇o2max (P < 0.05). These results suggest both adipose biopsy techniques used in the current investigation are appropriate for histological, transcriptional, and translational level measurements in exercise physiology studies of nonobese women and men.NEW & NOTEWORTHY This study provides investigators with useful information related to adipose biopsy sampling approaches that can be used when planning studies that use measurements of adipose histology, as well as measurements at the mRNA and protein level. Adipose periumbilical sampling with the Bergström biopsy needle and the Mercedes wet mini-liposuction technique are both appropriate options for studies in exercise physiology and in nonobese individuals.

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±2y) completed muscle power (6x4 sec; peak muscle power: 1369±86W) and VO2max (13±1min; 3.2±0.2L/min) tests on specially designed supine cycle ergometers during two separate trials. Blood catecholamines and lactate were measured pre, immediately post, and 4h 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 4h 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 VO2max test altered (p≤0.05) norepinephrine (+1394%), epinephrine (+1412%), 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 countermeasures for astronauts and Earth-based populations (e.g., aging individuals).

Microgravity-induced skeletal muscle atrophy in women and men: implications for long-duration spaceflights to the Moon and Mars.

The inclusion of women on spaceflights has historically been limited. Recently, the first woman who will travel to the Moon was selected, and more women are participating in long-duration spaceflights. However, physiological data from real and simulated microgravity exposure are limited in women. This investigation studied women (n = 8, 34 ± 1 yr) and men (n = 9, 32 ± 1 yr) who underwent 2 (women) or 3 (men) mo of simulated microgravity (6° head-down tilt bed rest). Quadriceps and triceps surae muscle volumes were assessed via MRI before bed rest, bed rest day 29 (BR29, women and men), bed rest day 57 (BR57, women), and bed rest day 89 (BR89, men). Volume of both muscle groups decreased (P < 0.05) in women and men at all bed rest timepoints. Quadriceps muscle volume loss in women was greater than men at 1 mo (BR29: -17% vs. -10%, P < 0.05) and this 1-mo loss for women was similar to men at 3 mo (BR89: -18%, P > 0.05). In addition, the loss in women at 2 mo (BR57: -21%) exceeded men at 3 mo (P < 0.05). For the triceps surae, there was a trend for greater muscle volume loss in women compared with men at 1 mo (BR29: -18% vs. -16%, P = 0.08), and loss in women at 2 mo was similar to men at 3 mo (BR57: -29%, BR89: -29%, P > 0.05). The collective evidence suggests that women experience greater lower limb muscle atrophy than men at least through the first 4 mo of microgravity exposure. More sex-specific microgravity studies are needed to help protect the health of women traveling on long-duration orbital and interplanetary spaceflights.NEW & NOTEWORTHY This study adds to the limited evidence regarding sex-specific responses to real or simulated microgravity exposure, which collectively suggests a sex-specific muscle atrophy profile, with women losing more than men at least through the first 4 mo of weightlessness. Considering the increase in women being selected for space missions, including the first women to travel to the Moon, more physiological data on women in response to microgravity are needed.

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.

Postabsorptive muscle protein synthesis is higher in outpatients as compared to inpatients.

Several factors affect muscle protein synthesis (MPS) in the postabsorptive state. Extreme physical inactivity (e.g., bedrest) may reduce basal MPS, whereas walking may augment basal MPS. We hypothesized that outpatients would have a higher postabsorptive MPS than inpatients. To test this hypothesis, we conducted a retrospective analysis. We compared 152 outpatient participants who arrived at the research site the morning of the MPS assessment with 350 Inpatient participants who had an overnight stay in the hospital unit before the MPS assessment the following morning. We used stable isotopic methods and collected vastus lateralis biopsies ∼2 to 3 h apart to assess mixed MPS. MPS was ∼12% higher (P < 0.05) for outpatients than inpatients. Within a subset of participants, we discovered that after instruction to limit activity, outpatients (n = 13) took 800 to 900 steps in the morning to arrive at the unit, seven times more steps than inpatients (n = 12). We concluded that an overnight stay in the hospital as an inpatient is characterized by reduced morning activity and causes a slight but significant reduction in MPS compared with participants studied as outpatients. Researchers should be aware of physical activity status when designing and interpreting MPS results.NEW & NOTEWORTHY The postabsorptive muscle protein synthesis rate is lower in the morning after an overnight inpatient hospital stay compared with an outpatient visit. Although only a minimal amount of steps was conducted by outpatients (∼900), this was enough to increase postabsorptive muscle protein synthesis rate.

Multitissue responses to exercise: a MoTrPAC feasibility study.

We assessed the feasibility of the Molecular Transducers of Physical Activity Consortium (MoTrPAC) human adult clinical exercise protocols, while also documenting select cardiovascular, metabolic, and molecular responses to these protocols. After phenotyping and familiarization sessions, 20 subjects (25 ± 2 yr, 12 M, 8 W) completed an endurance exercise bout (n = 8, 40 min cycling at 70% V̇o2max), a resistance exercise bout (n = 6, ∼45 min, 3 sets of ∼10 repetition maximum, 8 exercises), or a resting control period (n = 6, 40 min rest). Blood samples were taken before, during, and after (10 min, 2 h, and 3.5 h) exercise or rest for levels of catecholamines, cortisol, glucagon, insulin, glucose, free fatty acids, and lactate. Heart rate was recorded throughout exercise (or rest). Skeletal muscle (vastus lateralis) and adipose (periumbilical) biopsies were taken before and ∼4 h following exercise or rest for mRNA levels of genes related to energy metabolism, growth, angiogenesis, and circadian processes. Coordination of the timing of procedural components (e.g., local anesthetic delivery, biopsy incisions, tumescent delivery, intravenous line flushes, sample collection and processing, exercise transitions, and team dynamics) was reasonable to orchestrate while considering subject burden and scientific objectives. The cardiovascular and metabolic alterations reflected a dynamic and unique response to endurance and resistance exercise, whereas skeletal muscle was transcriptionally more responsive than adipose 4 h postexercise. In summary, the current report provides the first evidence of protocol execution and feasibility of key components of the MoTrPAC human adult clinical exercise protocols. Scientists should consider designing exercise studies in various populations to interface with the MoTrPAC protocols and DataHub.NEW & NOTEWORTHY This study highlights the feasibility of key aspects of the MoTrPAC adult human clinical protocols. This initial preview of what can be expected from acute exercise trial data from MoTrPAC provides an impetus for scientists to design exercise studies to interlace with the rich phenotypic and -omics data that will populate the MoTrPAC DataHub at the completion of the parent protocol.

Influence of aspirin on aging skeletal muscle: Insights from a cross-sectional cohort of septuagenarians.

Aspirin is one of the most commonly consumed cyclooxygenase (COX)-inhibitors and anti-inflammatory drugs and has been shown to block COX-produced regulators of inflammation and aging skeletal muscle size. We used propensity score matching to compare skeletal muscle characteristics of individuals from the Health ABC study that did not consume aspirin or any other COX-inhibiting drugs (non-consumers, n = 497, 74 ± 3 year, 168 ± 9 cm, 75.1 ± 13.8 kg, 33.1 ± 7.4% body fat, 37% women, 34% black) to those that consumed aspirin daily (and not any other COX-inhibiting drugs) and for at least 1 year (aspirin consumers, n = 515, 74 ± 3 year, 168 ± 9 cm, 76.2 ± 13.6 kg, 33.8 ± 7.1% body fat, 39% women, 30% black, average aspirin consumption: 6 year). Subjects were matched (p > 0.05) based on age, height, weight, % body fat, sex, and race (propensity scores: 0.33 ± 0.09 vs. 0.33 ± 0.09, p > 0.05). There was no difference between non-consumers and aspirin consumers for computed tomography-determined muscle size of the quadriceps (103.5 ± 0.9 vs. 104.9 ± 0.8 cm2 , p > 0.05) or hamstrings (54.6 ± 0.5 vs. 54.9 ± 0.5 cm2 , p > 0.05), or quadriceps muscle strength (111.1 ± 2.0 vs. 111.7 ± 2.0 Nm, p > 0.05). However, muscle attenuation (i.e., density) was higher in the aspirin consumers in the quadriceps (40.9 ± 0.3 vs. 44.4 ± 0.3 Hounsfield unit [HU], p < 0.05) and hamstrings (27.7 ± 0.4 vs. 33.2 ± 0.4 HU, p < 0.05). These cross sectional data suggest that chronic aspirin consumption does not influence age-related skeletal muscle atrophy, but does influence skeletal muscle composition in septuagenarians. Prospective longitudinal investigations remain necessary to better understand the influence of chronic COX regulation on aging skeletal muscle health.

Muscle group-specific skeletal muscle aging: a 5-yr longitudinal study in septuagenarians.

There is some evidence that the age-associated change in skeletal muscle mass is muscle specific, yet the number of specific muscles that have been studied to form our understanding in this area is limited. In addition, few aging investigations have examined multiple muscles in the same individuals. This longitudinal investigation compared changes in skeletal muscle size via computed tomography of the quadriceps (rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius), hamstrings (biceps femoris short and long heads, semitendinosus, and semimembranosus), psoas, rectus abdominis, lateral abdominals (obliques and transversus abdominis), and paraspinal muscles (erector spinae and multifidi) of older individuals from the Health, Aging, and Body Composition (Health ABC) study at baseline and 5.0 ± 0.1 years later (n = 469, 73 ± 3 yr and 78 ± 3 yr, 49% women, 33% black). Skeletal muscle size decreased (P < 0.05) in quadriceps (-3.3%), hamstrings (-5.9%), psoas (-0.4%), and rectus abdominis (-7.0%). The hamstrings and rectus abdominis atrophied approximately twice as much as the quadriceps (P < 0.05), whereas the quadriceps atrophied substantially more than the psoas (P < 0.05). The lateral abdominals (+5.9%) and paraspinals (+4.3%) hypertrophied (P < 0.05) to a similar degree (P > 0.05) over the 5 years. These data suggest that older individuals experience skeletal muscle atrophy and hypertrophy in a muscle group-specific fashion in the eighth decade, a critical time period in the aging process. A broader understanding of muscle group-specific skeletal muscle aging is needed to better guide exercise programs and other interventions that mitigate decrements in physical function with aging.NEW & NOTEWORTHY These longitudinal analyses of six muscle groups in septuagenarians provide novel information on the muscle group-specific aging process. Although the quadriceps, hamstrings, psoas, and rectus abdominis atrophied with different magnitudes, the lateral abdominals and paraspinals hypertrophied over the 5 years. These findings contribute to a better understanding of the skeletal muscle aging process and highlight the need to complete studies in this area with a muscle-specific focus.

Controlling Inflammation Improves Aging Skeletal Muscle Health.

Chronic inflammation is associated with a decline in aging skeletal muscle health. Inflammation also seems to interfere with the beneficial skeletal muscle adaptations conferred by exercise training in older individuals. We hypothesize that the cyclooxygenase pathway is partially responsible for this negative inflammatory influence on aging skeletal muscle health and plasticity.

Human skeletal muscle-specific atrophy with aging: a comprehensive review.

Age-related skeletal muscle atrophy appears to be a muscle group-specific process, yet only a few specific muscles have been investigated and our understanding in this area is limited. This review provides a comprehensive summary of the available information on age-related skeletal muscle atrophy in a muscle-specific manner, nearly half of which comes from the quadriceps. Decline in muscle-specific size over ∼50 yr of aging was determined from 47 cross-sectional studies of 982 young (∼25 yr) and 1,003 old (∼75 yr) individuals and nine muscle groups: elbow extensors (-20%, -0.39%/yr), elbow flexors (-19%, -0.38%/yr), paraspinals (-24%, -0.47%/yr), psoas (-29%, -0.58%/yr), hip adductors (-13%, -0.27%/yr), hamstrings (-19%, -0.39%/yr), quadriceps (-27%, -0.53%/yr), dorsiflexors (-9%, -0.19%/yr), and triceps surae (-14%, -0.28%/yr). Muscle-specific atrophy rate was also determined for each of the subcomponent muscles in the hamstrings, quadriceps, and triceps surae. Of all the muscles included in this review, there was more than a fivefold difference between the least (-6%, -0.13%/yr, soleus) to the most (-33%, -0.66%/yr, rectus femoris) atrophying muscles. Muscle activity level, muscle fiber type, sex, and timeline of the aging process all appeared to have some influence on muscle-specific atrophy. Given the large range of muscle-specific atrophy and the large number of muscles that have not been investigated, more muscle-specific information could expand our understanding of functional deficits that develop with aging and help guide muscle-specific interventions to improve the quality of life of aging women and men.

Human skeletal muscle size with ultrasound imaging: a comprehensive review.

Skeletal muscle size is an important factor in assessing adaptation to exercise training and detraining, athletic performance, age-associated atrophy and mobility decline, clinical conditions associated with cachexia, and overall skeletal muscle health. Magnetic resonance (MR) imaging and computed tomography (CT) are widely accepted as the gold standard methods for skeletal muscle size quantification. However, it is not always feasible to use these methods (e.g., field studies, bedside studies, and large cohort studies). Ultrasound has been available for skeletal muscle examination for more than 50 years and the development, utility, and validity of ultrasound imaging are underappreciated. It is now possible to use ultrasound in situations where MR and CT imaging are not suitable. This review provides a comprehensive summary of ultrasound imaging and human skeletal muscle size assessment. Since the first study in 1968, more than 600 articles have used ultrasound to examine the cross-sectional area and/or volume of 107 different skeletal muscles in more than 27,500 subjects of various ages, health status, and fitness conditions. Data from these studies, supported by decades of technological developments, collectively show that ultrasonography is a valid tool for skeletal muscle size quantification. Considering the wide-ranging connections between human health and function and skeletal muscle mass, the utility of ultrasound imaging will allow it to be employed in research investigations and clinical practice in ways not previously appreciated or considered.

Skeletal muscle transcriptome response to a bout of endurance exercise in physically active and sedentary older adults.

Age-related declines in cardiorespiratory fitness and physical function are mitigated by regular endurance exercise in older adults. This may be due, in part, to changes in the transcriptional program of skeletal muscle following repeated bouts of exercise. However, the impact of chronic exercise training on the transcriptional response to an acute bout of endurance exercise has not been clearly determined. Here, we characterized baseline differences in muscle transcriptome and exercise-induced response in older adults who were active/endurance trained or sedentary. RNA-sequencing was performed on vastus lateralis biopsy specimens obtained before, immediately after, and 3 h following a bout of endurance exercise (40 min of cycling at 60%-70% of heart rate reserve). Using a recently developed bioinformatics approach, we found that transcript signatures related to type I myofibers, mitochondria, and endothelial cells were higher in active/endurance-trained adults and were associated with key phenotypic features including V̇o2peak, ATPmax, and muscle fiber proportion. Immune cell signatures were elevated in the sedentary group and linked to visceral and intermuscular adipose tissue mass. Following acute exercise, we observed distinct temporal transcriptional signatures that were largely similar among groups. Enrichment analysis revealed catabolic processes were uniquely enriched in the sedentary group at the 3-h postexercise timepoint. In summary, this study revealed key transcriptional signatures that distinguished active and sedentary adults, which were associated with difference in oxidative capacity and depot-specific adiposity. The acute response signatures were consistent with beneficial effects of endurance exercise to improve muscle health in older adults irrespective of exercise history and adiposity.NEW & NOTEWORTHY Muscle transcript signatures associated with oxidative capacity and immune cells underlie important phenotypic and clinical characteristics of older adults who are endurance trained or sedentary. Despite divergent phenotypes, the temporal transcriptional signatures in response to an acute bout of endurance exercise were largely similar among groups. These data provide new insight into the transcriptional programs of aging muscle and the beneficial effects of endurance exercise to promote healthy aging in older adults.

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 (V̇o2max): 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.

Influence of low-dose aspirin, resistance exercise, and sex on human skeletal muscle PGE2 /COX pathway activity.

Prostaglandin (PG) E2  has been linked to increased inflammation and attenuated resistance exercise adaptations in skeletal muscle. Nonaspirin cyclooxygenase (COX) inhibitors have been shown to reduce these effects. This study examined the effect of low-dose aspirin on skeletal muscle COX production of PGE2 at rest and following resistance exercise. Skeletal muscle (vastus lateralis) biopsies were taken from six individuals (4 M/2 W) before and 3.5 hr after a single bout of resistance exercise for ex vivo PGE2 production under control and low (10 µM)- or standard (100 µM)-dose aspirin conditions. Sex-specific effects of aspirin were also examined by combining the current findings with our previous similar ex vivo skeletal muscle investigations (n = 20, 10 M/10 W). Low-dose aspirin inhibited skeletal muscle PGE2 production (p < 0.05). This inhibition was similar to standard-dose aspirin (p > 0.05) and was not influenced by resistance exercise (p > 0.05) (overall effect: -18 ± 5%). Men and women had similar uninhibited skeletal muscle PGE2 production at rest (men: 1.97 ± 0.33, women: 1.96 ± 0.29 pg/mg wet weight/min; p > 0.05). However, skeletal muscle of men was 60% more sensitive to aspirin inhibition than women (p < 0.05). In summary, the current findings 1) confirm low-dose aspirin inhibits the PGE2 /COX pathway in human skeletal muscle, 2) show that resistance exercise does not alter aspirin inhibitory efficacy, and 3) suggest the skeletal muscle of men and women could respond differently to long-term consumption of low-dose aspirin, one of the most common chronically consumed drugs in the world.

Effects of aging and lifelong aerobic exercise on basal and exercise-induced inflammation in women.

Low muscle mass and frailty are especially prevalent in older women and may be accelerated by age-related inflammation. Habitual physical activity throughout the life span (lifelong exercise) may prevent muscle inflammation and associated pathologies, but this is unexplored in women. This investigation assessed basal and acute exercise-induced inflammation in three cohorts of women: young exercisers (YE, n = 10, 25 ± 1 yr, [Formula: see text]: 44 ± 2 mL/kg/min, quadriceps size: 59 ± 2 cm2), old healthy nonexercisers (OH, n = 10, 75 ± 1 yr, [Formula: see text]: 18 ± 1 mL/kg/min, quadriceps size: 40 ± 1 cm2), and lifelong aerobic exercisers with a 48 ± 2 yr aerobic training history (LLE, n = 7, 72 ± 2 yr, [Formula: see text]: 26 ± 2 mL/kg/min, quadriceps size: 42 ± 2 cm2). Resting serum IL-6, TNF-α, C-reactive protein (CRP), and IGF-1 were measured. Vastus lateralis muscle biopsies were obtained at rest (basal) and 4 h after an acute exercise challenge (3 × 10 reps, 70% 1-repetition maximum) to assess gene expression of cytokines (IL-6, TNF-α, IL-1ß, IL-10, IL-4, IL-1Ra, TGF-ß), chemokines (IL-8, MCP-1), cyclooxygenase enzymes (COX-1, COX-2), prostaglandin E2 synthases (mPGES-1, cPGES) and receptors (EP3-4), and macrophage markers (CD16b, CD163), as well as basal macrophage abundance (CD68+ cells). The older cohorts (LLE + OH combined) demonstrated higher muscle IL-6 and COX-1 (P ≤ 0.05) than YE, whereas LLE expressed lower muscle IL-1ß (P ≤ 0.05 vs. OH). Acute exercise increased muscle IL-6 expression in YE only, whereas the older cohorts combined had the higher postexercise expression of IL-8 and TNF-α (P ≤ 0.05 vs. YE). Only LLE had increased postexercise expression of muscle IL-1ß and MCP-1 (P ≤ 0.05 vs. preexercise). Thus, aging in women led to mild basal and exercise-induced inflammation that was unaffected by lifelong aerobic exercise, which may have implications for long-term function and adaptability.NEW & NOTEWORTHY We previously reported a positive effect of lifelong exercise on skeletal muscle inflammation in aging men. This parallel investigation in women revealed that lifelong exercise did not protect against age-related increases in circulating or muscle inflammation and that preparedness to handle loading stress was not preserved by lifelong exercise. Further investigation is necessary to understand why lifelong aerobic exercise may not confer the same anti-inflammatory benefits in women as it does in men.

Low-dose aspirin and COX inhibition in human skeletal muscle.

Skeletal muscle health has been shown to benefit from regular consumption of cyclooxygenase (COX)-inhibiting drugs. Aspirin, especially at low doses, is one of the most commonly consumed COX inhibitors, yet investigations of low-dose aspirin effects on skeletal muscle are nonexistent. The goal of this study was to examine the efficacy of low-dose aspirin on skeletal muscle COX production of the inflammatory regulator prostaglandin (PG)E2 at rest and after exercise. Skeletal muscle biopsies (vastus lateralis) were taken from eight individuals [4 men, 4 women; 25 ± 1 yr; 81.4 ± 3.4 kg; maximal oxygen consumption (V̇o2max): 3.33 ± 0.21 L/min] before and 3.5 h after 40 min of cycling at 70% of V̇o2max for the measurement of ex vivo PGE2 production. Muscle strips were incubated in Krebs-Henseleit buffer (control) or supplemented with one of two aspirin concentrations that reflected blood levels after a low (10 µM; typical oral dose: 75-325 mg) or standard (100 µM; typical oral dose: 975-1,000 mg) dose. Low (-22 ± 5%)- and standard (-28 ± 5%)-dose aspirin concentrations both reduced skeletal muscle PGE2 production, independent of exercise (P < 0.05). There was no difference in PGE2 suppression between the two doses (P > 0.05). In summary, low-dose aspirin levels are sufficient to inhibit the COX enzyme in skeletal muscle and significantly reduce production of PGE2, a known regulator of skeletal muscle health. Aerobic exercise does not appear to alter the inhibitory efficacy of aspirin. These findings may have implications for the tens of millions of individuals who chronically consume low-dose aspirin.NEW & NOTEWORTHY This study demonstrated that even low-dose aspirin concentrations can significantly reduce the prostaglandin (PG)E2/cyclooxygenase (COX) pathway activity in human skeletal muscle and this effect is not altered during the recovery period following aerobic exercise. These findings are noteworthy since aspirin is one of the most commonly consumed drugs in the world and nonaspirin COX-inhibiting drugs have been shown to regulate skeletal muscle health in sedentary and exercise-training individuals.

Effects of aging and lifelong aerobic exercise on expression of innate immune components in human skeletal muscle.

The purpose of this investigation was to evaluate the effects of aging and lifelong exercise on skeletal muscle components of the innate immune system. Additionally, the effects of an acute resistance exercise (RE) challenge were explored. Three groups of men were studied: young exercisers (YE: n = 10, 25 ± 1 yr; V̇o2max: 53 ± 3 mL/kg/min; quadriceps size: 78 ± 3 cm2), lifelong aerobic exercisers with a 53 ± 1 yr training history (LLE; n = 21, 74 ± 1 yr; V̇o2max: 34 ± 1 mL/kg/min; quadriceps size: 67 ± 2 cm2), and old healthy nonexercisers (OH: n = 10, 75 ± 1 yr; V̇o2max: 22 ± 1 mL/kg/min, quadriceps size: 56 ± 3 cm2). Vastus lateralis muscle biopsies were obtained in the basal state and 4 h after RE (3 × 10 reps, 70% of 1 repetition maximum) to assess Toll-like receptors (TLR)1-10, TLR adaptors (Myd88 and TRIF), and NF-κB pathway components (IκΒα and IKKß) mRNA expression. Basal TLR3, TLR6, and TLR7 tended to be higher (P ≤ 0.10) with aging (LLE and OH combined). In general, RE increased expression of TLR1 and TLR8 (P ≤ 0.10) and TLR3 and TLR4 (P < 0.05), although TLR3 did not respond in OH. Both TLR adaptors also responded to the exercise bout; these were primarily (Myd88, main effect P ≤ 0.10) or exclusively (TRIF, P < 0.05) driven by the OH group. In summary, aging appears to increase basal expression of some innate immune components in human skeletal muscle, and lifelong aerobic exercise does not affect this age-related increase. An exercise challenge stimulates the expression of several TLRs, while the TLR adaptor response appears to be dysregulated with aging and maintained with lifelong exercise. Partially preserved muscle mass, coupled with a notable immunity profile, suggests lifelong exercisers are likely better prepared for a stress that challenges the immune system.NEW & NOTEWORTHY Findings from this investigation provide novel insight into the effect of aging and lifelong aerobic exercise on structural components of the innate immune system in skeletal muscle of humans. Data presented here suggest aging increases basal expression of select Toll-like receptors (TLRs), and lifelong exercise does not impact this age-related increase. Additionally, acute exercise stimulates gene expression of several TLRs, while the adaptor response is likely dysregulated with aging and maintained with lifelong exercise.