-related -myosin mutations cause highly variable calcium sensitivity with functional imbalances among individual muscle cells.
Assessment of the functional capacity of the cardiovascular system is essential in sports medicine. For athletes, the maximal oxygen uptake [Formula: see text] provides valuable information about their aerobic power. In the clinical setting, the (VO(2max)) provides important diagnostic and prognostic information in several clinical populations, such as patients with coronary artery disease or heart failure. Likewise, VO(2max) assessment can be very important to evaluate fitness in asymptomatic adults. Although direct determination of [VO(2max) is the most accurate method, it requires a maximal level of exertion, which brings a higher risk of adverse events in individuals with an intermediate to high risk of cardiovascular problems. Estimation of VO(2max) during submaximal exercise testing can offer a precious alternative. Over the past decades, many protocols have been developed for this purpose. The present review gives an overview of these submaximal protocols and aims to facilitate appropriate test selection in sports, clinical, and home settings. Several factors must be considered when selecting a protocol: (i) The population being tested and its specific needs in terms of safety, supervision, and accuracy and repeatability of the VO(2max) estimation. (ii) The parameters upon which the prediction is based (e.g. heart rate, power output, rating of perceived exertion [RPE]), as well as the need for additional clinically relevant parameters (e.g. blood pressure, ECG). (iii) The appropriate test modality that should meet the above-mentioned requirements should also be in line with the functional mobility of the target population, and depends on the available equipment. In the sports setting, high repeatability is crucial to track training-induced seasonal changes. In the clinical setting, special attention must be paid to the test modality, because multiple physiological parameters often need to be measured during test execution. When estimating VO(2max), one has to be aware of the effects of medication on heart rate-based submaximal protocols. In the home setting, the submaximal protocols need to be accessible to users with a broad range of characteristics in terms of age, equipment, time available, and an absence of supervision. In this setting, the smart use of sensors such as accelerometers and heart rate monitors will result in protocol-free VO(2max) assessments. In conclusion, the need for a low-risk, low-cost, low-supervision, and objective evaluation of VO(2max) has brought about the development and the validation of a large number of submaximal exercise tests. It is of paramount importance to use these tests in the right context (sports, clinical, home), to consider the population in which they were developed, and to be aware of their limitations.
A primary muscle cell culture derived from newborn rabbit muscle and growing on microcarriers in suspension was established. When cultured for several weeks, the myotubes in this model develop the completely adult pattern of fast myosin light and heavy chains. When Ca 2؉ ionophore is added to the culture medium on day 11, raising intracellular [Ca 2؉ ] about 10-fold, the myotubes develop to exhibit properties of an adult slow muscle by day 30, expressing slow myosin light as well as heavy chains, elevated citrate synthase, and reduced lactate dehydrogenase. The remarkable plasticity of these myotubes becomes apparent, when 8 days after withdrawal of the ionophore a marked slow-to-fast transition, as judged from the expression of isomyosins and metabolic enzymes, occurs.While the alterations that occur in mammalian muscle during fast-to-slow transition in vivo are known in great detail, mostly from chronic electrostimulation experiments with fast hindlimb muscles (1), the information on the mechanism initiating this process is sparse. A reduced intracellular phosphorylation potential and an elevated intracellular Ca 2ϩ concentration ([Ca 2ϩ ] i ), as they occur during sustained contractile activity, have been discussed as possible trigger events (2-5). It was our aim to test whether an increase in [Ca 2ϩ ] i imposed on the muscle cell is indeed able to induce a fast-to-slow transition. Because such an experiment cannot be performed in vivo, we were searching for a suitable myogenic cell culture system in which this would become feasible.Thus, this paper has two goals: (i) to report how a primary muscle culture can be grown that develops into an adult-like state, expressing adult myosin of the fast type only, and (ii) to study whether manipulation of [Ca 2ϩ ] i induces a shift between ''fast'' and ''slow'' fiber properties in the cultured myotubes. We show, first, that myotubes derived from newborn rabbit muscles and grown for 4 weeks on microcarriers in suspension possess a purely adult fast myosin pattern. Second, we show that these myotubes exhibit a similarly remarkable plasticity as it is known for adult rabbit muscles (1). This plasticity becomes apparent during exposure of the myotubes to high [Ca 2ϩ ] i , which causes development of the slow isoforms of myosin light chains (MLCs) and myosin heavy chains (MHCs) instead of their fast counterparts, of an increased aerobic metabolic capacity accompanied by a decreased anaerobic capacity as evidenced from elevated citrate synthase (CS) and reduced lactate dehydrogenase (LDH) levels, and of an increased activity ratio of the carbonic anhydrases CA III/CA II. Lowering [Ca 2ϩ ] i back to normal levels is followed by a reversal of all these changes within a few days. EXPERIMENTAL PROCEDURESCulture and Harvesting of Muscle Cells. Newborn White New Zealand rabbits were killed by decapitation. Hindlimb muscles were cut in small pieces and incubated in BSS, pH 7.0 (4.56 mM KCl͞0.44 mM KH 2 PO 4 ͞0.42 mM Na 2 HPO 4 ͞25 mM NaHCO 3 ͞ 119.8 mM NaCl͞50 mg/...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.