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Samantha L. Winter and John H. Challis

For a physiologically realistic range of joint motion and therefore range of muscle fiber lengths, only part of the force-length curve can be used in vivo; i.e., the section of the force–length curve that is expressed can vary. The purpose of this study was to determine the expressed section of the force–length relationship of the gastrocnemius for humans. Fourteen male and fourteen female subjects aged 18–27 performed maximal isometric plantar flexions in a Biodex dynamometer. Plantar flexion moments were recorded at five ankle angles: −15°, 0°, 15°, 30°, and 40°, with negative angles defined as dorsiflexion. These measurements were repeated for four randomly ordered knee angles over two testing sessions 4 to 10 days apart. The algorithm of Herzog and ter Keurs (1988a) was used to reconstruct the force–length curves of the biarticular gastrocnemius. Twenty-four subjects operated over the ascending limb, three operated over the descending limb, and one operated over the plateau region. The variation found suggests that large subject groups should be used to determine the extent of normal in vivo variability in this muscle property. The possible source of the variability is discussed in terms of parameters typically used in muscle models.

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Hyeonki Choi and Ray Vanderby Jr.

This study developed a three-dimensional biomechanical model to investigate the internal loads on the human neck that result from isometrically generated loads resisted by a force on the head. The first goal was to apply the double-optimization (DOPT) method, the EMG-based method, and the EMG assisted optimization (EMGAO) method to the neck model, calculating muscle forces and C4/5 cervical joint loads for each method. The second goal was to compare the results of the different methods, and the third was to determine maximum exertion forces in the cervical spine for isometric contractions. To formulate the EMG-based model, electromyographic signals were collected from 10 male subjects. EMG signals were obtained from 8 sites around the C4/5 level of the neck by surface electrodes, while the subject performed near maximum, isometric exertions. The mean maximum values (±SD) calculated for C4/5 joint compressive forces during peak exertions were 1654 (±308) N in flexion by the EMG method, 1674 (±319) N in flexion by the EMGAO method, and 1208 (±123) N in extension by the DOPT method. In contrast to the DOPT method, the EMG and EMGAO methods showed activation of all the muscles, including the antagonists, and accommodated various load distribution patterns among the agonist muscles during generation of the same magnitude of moments, especially in lateral bending. The EMG and EMGAO methods predicted higher cervical spinal loads than previously published results by the DOPT method. These results may be helpful to engineers and surgeons who are designing and using cervical spine implants and instrumentation.

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David Preen, Brian Dawson, Carmel Goodman, John Beilby and Simon Ching

The purposes of this investigation were first to determine the impact of 3 different creatine (Cr) loading procedures on skeletal muscle total Cr (TCr) accumulation and, second, to evaluate the effectiveness of 2 maintenance regimes on retaining intramuscular TCr stores, in the 6 weeks following a 5-day Cr loading program (20 g · day−1). Eighteen physically active male subjects were divided into 3 equal groups and administered either: (a) Cr (4 X 5 g · day−1 X 5 days), (b) Glucose+Cr (1 g · kg−1 of body mass twice per day), or (c) Cr in conjunction with 60 min of daily muscular (repeated-sprint) exercise. Following the 5-day loading period, subjects were reassigned to 3 maintenance groups and ingested either 0 g · day−1, 2 g · day−1 or 5 g · day−1 of Cr for a period of 6 weeks. Muscle biopsy samples (vastus lateralis) were taken pre- and post-loading as well as post-maintenance and analyzed for skeletal muscle ATP, phosphocreatine (PCr), Cr, and TCr concentrations. Twenty-four hour urine samples were collected for each of the loading days and last 2 maintenance days, and used to determine whole body Cr retention. Post-loading TCr stores were significantly (p < .05) increased in all treatment conditions. The Glucose+Cr condition produced a greater elevation (p < .05) in TCr concentrations (25%) than the Cr Only (16%) or Exercise+Cr (18%) groups. Following the maintenance period, muscle TCr stores were still similar to post-loading values for both the 2 g · day−1 and 5 g · day−1 conditions. Intramuscular TCr values for the 0 g · day−1 condition were significantly lower than the other conditions after the 6-week period. Although not significantly different from pre-loading concentrations, muscle TCr for the 0 g · day−1 group had not fully returned to baseline levels at 6 weeks post-loading. The data suggests that Glucose+Cr (but with a much smaller glucose intake than currently accepted) is potentially the most effective means of elevating TCr accumulation in human skeletal muscle. Furthermore, after 5 days of Cr loading, elevated muscle TCr concentrations can be maintained by the ingestion of small daily Cr doses (2-5 g) for a period of 6 weeks and that TCr concentrations may take longer than currently accepted to return to baseline values after such a Cr loading regime.

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Xiaocai Shi and Dennis H. Passe

The purpose of this study is to summarize water, carbohydrate (CHO), and electrolyte absorption from carbohydrate- electrolyte (CHO-E) solutions based on all of the triple-lumen-perfusion studies in humans since the early 1960s. The current statistical analysis included 30 reports from which were obtained information on water absorption, CHO absorption, total solute absorption, CHO concentration, CHO type, osmolality, sodium concentration, and sodium absorption in the different gut segments during exercise and at rest. Mean differences were assessed using independent-samples t tests. Exploratory multiple-regression analyses were conducted to create prediction models for intestinal water absorption. The factors influencing water and solute absorption are carefully evaluated and extensively discussed. The authors suggest that in the human proximal small intestine, water absorption is related to both total solute and CHO absorption; osmolality exerts various impacts on water absorption in the different segments; the multiple types of CHO in the ingested CHO-E solutions play a critical role in stimulating CHO, sodium, total solute, and water absorption; CHO concentration is negatively related to water absorption; and exercise may result in greater water absorption than rest. A potential regression model for predicting water absorption is also proposed for future research and practical application. In conclusion, water absorption in the human small intestine is influenced by osmolality, solute absorption, and the anatomical structures of gut segments. Multiple types of CHO in a CHO-E solution facilitate water absorption by stimulating CHO and solute absorption and lowering osmolality in the intestinal lumen.

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Manuel Trinidad-Fernández, Manuel González-Sánchez and Antonio I. Cuesta-Vargas

the first use of this methodology in humans. This study aimed to evaluate a new, minimally invasive method of tracking internal and external rotation of the scapula using ultrasound imaging combined with the signal provided by a 3-dimensional electromagnetic sensor and to assess the reliability of

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Kevin Deschamps, Giovanni Matricali, Maarten Eerdekens, Sander Wuite, Alberto Leardini and Filip Staes

, Alexander RM . The spring in the arch of the human foot . Nature . 1987 ; 325 ( 6100 ): 147 – 149 . doi:10.1038/325147a0 10.1038/325147a0 3808070 9. Farley CT , Glasheen J , McMahon TA . Running springs: speed and animal size . J Exp Biol . 1993 ; 185 : 71 – 86 . PubMed ID: 8294853 8294853

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Eric D.B. Goulet

Glycerol-induced hyperhydration (GIH) has been shown to improve fluid retention and endurance performance compared with water-induced hyperhydration. The goal of this article is to report on what is known and unknown about how glycerol-containing hyperhydration solutions (GCHSs) are processed at the stomach and intestine level, propose strategies to improve the efficacy of GIH, and provide research questions for future studies. Through statistical analyses, it is demonstrated that the effectiveness of GCHSs in increasing fluid retention is maximized when fluid ingestion is in the upper range of what is normally administered by studies (~26 ml/kg body weight) and the duration of the protocol is no longer than the time it takes for the glycerol-fluid load to be totally or nearly completely integrated inside the body. The rate of gastric emptying and intestinal absorption of GCHSs is unknown. However, based on an analysis of indirect evidence obtained from human studies, it is proposed that most glycerol (~80 g) and fluid (~1,700 ml) ingested during a typical GIH protocol can be integrated inside the body within 60–90 min. Whether the stress associated with competition could alter these figures is unknown. Research in rats indicates that combining glycerol with glucose at a 3:1 ratio accelerates intestinal absorption of both glycerol and water, thereby potentially improving the efficacy of GIH. Human studies must be conducted to determine how GCHSs are processed by the gastrointestinal system and whether adding glucose to GCHSs could improve the technique’s efficacy.

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Keitaro Kubo, Hiroaki Kanehisa and Tetsuo Fukunaga

The purposes of this study were to compare the elasticity of tendon and aponeurosis in human knee extensors and ankle plantar flexors in vivo and to examine whether the maximal strain of tendon was correlated to that of aponeurosis. The elongation of tendon and aponeurosis during isometric knee extension (n = 23) and ankle plantar flexion (n = 22), respectively, were determined using a real-time ultrasonic apparatus, while the participants performed ramp isometric contractions up to voluntary maximum. To calculate the strain values from the measured elongation, we measured the respective length of tendon and aponeurosis. For the knee extensors, the maximal strain of aponeurosis (12.1 ± 2.8%) was significantly greater than that of the patella tendon (8.3 ± 2.4%), p < 0.001. On the contrary, the maximal strain of Achilles tendon (5.9 ± 1.4%) was significantly greater than that of aponeurosis in ankle plantar flexors (2.7 ± 1.4%), p < 0.001. Furthermore, for both knee extensors and ankle plantar flexors there was no significant correlation between maximal strain of tendon and aponeurosis. These results would be important for understanding the different roles of tendon and aponeurosis during human movements and for more accurate muscle modeling.

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Roy L.P.G. Jentjens and Asker E. Jeukendrup

Vanadium compounds have been shown to have insulin-like properties in rats and non-insulin-dependent diabetic humans. The purpose of the present study was to examine whether the effects of acute and short-term administration of vanadyl sulphate (VS) on insulin sensitivity also exist in healthy active individuals. Five male and 2 female participants (age: 24.9 ± 1.5 years; height: 176.1 ± 2.9 cm; body mass: 70.1 ± 2.9 kg) underwent 3 oral glucose tolerance tests (OGTT). The first OGTT was performed to obtain a baseline index of insulin sensitivity (ISI). On the night preceding the second OGTT, participants ingested 100 mg of VS, and the acute effects of VS on ISI were examined. For the next 6 days, participants were instructed to ingest 50 mg of VS twice daily, and a final OGTT was performed on day 7 to determine the short-term effects of VS on ISI. No differences were found in fasting plasma glucose and insulin concentrations after VS administration. Furthermore, ISI after 1 day and 7 days of VS administration was not different compared with baseline ISI (4.8±0.1 vs. 4.7±0.1 vs. 4.7 ± 0.1, respectively). These results demonstrate that there are no acute and short-term effects of VS administration on insulin sensitivity in healthy humans.

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Andy Roosen, Matthew T.G. Pain and Mickaël Begon

Much research is ongoing into improving the accuracy of functional algorithms to determine joint centers (JC), but there has been limited testing using human movement data. This paper is in three parts: Part 1, errors in determining JCs from real human movement data using the SCoRE method; Part 2, variability of marker combinations during a punch; Part 3, variability in the JC due to reconstruction. Results indicate determining the JC of the shoulder or elbow with a triad of markers per segment with an accuracy greater than 20 mm is unlikely. Part 2 suggests conducting a pilot study with abundant markers to obtain triads, which are most stable due to differences of 300–400% in variability between triads. Variability due to the choice of reference frame for reconstruction during the punch ranged from 2.5 to 13.8 mm for the shoulder and 1.5 to 21.1 mm for the elbow. It would appear more pertinent to enhance the practical methods in situ than to further improve theoretical accuracy of functional methods.