The purpose of this study was to evaluate the influence knee joint range motion (RoM) on torque–velocity relationship and fatigue in extensor muscles 7 young (median = 26 y) older (68 adults. Each leg assigned a RoM (35° or 75°) over which perform protocol (maximal isokinetic contractions, 60–300°·s −1 ) (120 maximal contractions at 120°·s , 0.5 Hz). Six participants were unable reach 300°·s 35°. Therefore, velocity eliciting 75% peak torque 60°·s ( V 75 °·s calculated for each from fit...

The cause and consequences of inosine monophosphate (IMP) formation when ATP declines during muscular contractions in vivo are not fully understood. purpose this study was to examine the role IMP maintenance Gibbs free energy for hydrolysis (∆G ) dynamic increasing workload, implications loss vivo. Eight males (27.5, 25-35yr, median, range) completed an 8-minute incremental protocol (2-minute stages isotonic knee extensions (0.5Hz)) a 3-Tesla magnetic resonance (MR) system. Phosphorus MR...

In addition to its role in substrate selection (carbohydrate vs. fat) for oxidative metabolism muscle, acetylcarnitine production may be an important modulator of the energetic pathway by which ATP is produced. A combination noninvasive magnetic resonance spectroscopy measures cytosolic and pathways was used investigate link between [acetylcarnitine] energy vivo. Intracellular metabolites were measured vastus lateralis muscle eight males (mean: 28.4 yr, range: 25-35) during 8 min...

Previous studies of age-related differences in substrate oxidation over 24 hours and during exercise have provided divergent results, leaving it unclear whether is influenced by aging. PURPOSE: Evaluate distinct periods a 24-hr stay room calorimeter: the full hours, activities daily living (ADLs), 30-min treadmill walk at 1.3 m·s-1 (30MTW). METHODS: Peak O2 uptake (VO2peak) was determined from an incremental test 9 young (Y, 28 ± 3 yr) 6 older (O, 71 5 healthy males. On separate visit,...

Although it is clear that the metabolic basis of skeletal muscle fatigue (a transient decrease in peak torque or power response to contraction) involves accumulation intracellular H+ (decreased pH) and inorganic phosphate (Pi), effects age on contraction-induced these metabolites has not been evaluated systematically. PURPOSE: Compare pH [Pi] young (18-45 yr) older (55-85 vivo following contractions evaluate influence contraction mode. METHODS: PubMed, Web Science, SPORTDiscus were searched...

The interplay in vivo between muscle bioenergetics (ATP production) and intermediary metabolism working skeletal is not fully understood. During contractions, acetylcarnitine (AC) production may be an important modulator of energetic pathway fuel selection for the support ATP production. As contraction intensity demand increase, free carnitine mitochondria buffers excess acetyl-CoA by converting it into AC CoA. This process enables greater flux pyruvate lessening acetyl-CoA's product...

Perturbations to the intracellular milieu during muscular work can include accumulation of fatigue-inducing metabolites in skeletal muscle. It has been suggested that oxygen availability contributes fatigue by limiting bioenergetic pathways support contractile activity. Our purpose was examine role (PO2 ) disruption muscle bioenergetics and consequent vivo. We hypothesized (decrease peak power) would be associated with acidosis inorganic phosphate (Pi), but not PO2 , which remain above...

Traditionally, it has been accepted that working muscle will endeavor to maintain [ATP] near its resting level in order a favorable free energy of ATP hydrolysis (∆GATP). Recent reports significant declines during maximal muscular contractions vivo spark new interest this concept. is hydrolyzed adenosine diphosphate (ADP) the creatine kinase reaction provide directly ATPases. As needed, additional can be provided by breakdown ADP monophosphate (AMP), which rapidly cleared formation inosine...

Intramyocellular ATP depletion can occur during intense muscle contractions if demand exceeds production. If conditions are sufficiently severe, this lead to a loss of total adenine nucleotides (TAN) in the irreversible step from adenosine monophosphate (AMP) inosine (IMP). The occurrence and bioenergetic implications following vivo not clear. PURPOSE: To understand evolution resolution changes ATP, phosphomonoesters (PME; glucose-6-phosphate (G6P) + IMP), TAN fatiguing humans. METHODS:...

While it is well accepted that muscle fatigue (transient decrease in peak torque) task-specific, little information exists regarding the influence of joint range motion (ROM) on fatigue. Further, given age-related changes torque-velocity (T-V) relationship, reasonable to expect ROM may differently young and older muscle. PURPOSE: To determine effect knee extensor characteristics adults. METHODS: After providing written informed consent, 7 (29 ± 5 yr, 5F) (70 4, 4F) adults had each leg...

While the bioenergetics of working skeletal muscle have been well-studied in humans, impact energetic characteristics on performance everyday mobility tasks is less clear. PURPOSE: To evaluate relationships between oxidative and non-oxidative bioenergetic variables, an indicator substrate use (acetylcarnitine), whole-body energy metabolism during a standardized activity. METHODS: After obtaining written consent, intramyocellular energetics were measured vivo vastus lateralis 7 males (mean...

Indirect calorimetry is used to measure oxygen consumption (VO2, mL/min) and carbon dioxide production (VCO2, mL/min), which in turn are calculate the respiratory exchange ratio (RER) energy expenditure (EE, kcal/min). Commonly, these measurements made using metabolic carts, but emergence of sophisticated whole-room calorimeters provides opportunity evaluate variables under conditions more closely approximating "real life." Understanding reliability humans important for detecting meaningful...