Medicine and Science in Sports and Exercise
Effect of Chronic Exercise on Appetite Control in Overweight and Obese Individuals
Wed, 05/01/2013 - 05:00Purpose: The effect of exercise on body mass is likely to be partially mediated through changes in appetite control. However, no studies have examined the effect of chronic exercise on obestatin and cholecystokinin (CCK) plasma concentrations or the sensitivity to detect differences in preload energy in obese individuals. The objective of this study was to investigate the effects of chronic exercise on 1) fasting and postprandial plasma concentrations of obestatin, CCK, leptin, and glucose insulinotropic peptide (GIP) and 2) the accuracy of energy compensation in response to covert preload manipulation. Methods: This study used a 12-wk supervised exercise program in 22 sedentary overweight/obese individuals. Fasting/postprandial plasma concentrations of obestatin, CCK, leptin, and GIP were assessed before and after the intervention. Energy compensation at a 30-min test meal after a high-energy (607 kcal) or a low-energy (246 kcal) preload and for the rest of the day (cumulative energy intake [EI]) was also measured. Results: There was a significant reduction in the plasma concentration of fasting plasma GIP and both fasting and postprandial leptin concentrations after the exercise intervention (P < 0.05 for all). No significant changes were observed for CCK or obestatin. A significant preload–exercise interaction (P = 0.011) was observed on cumulative EI and energy compensation for the same period (−87% ± 196% vs 68% ± 165%, P = 0.011). Weight loss (3.5 ± 1.4 kg, P < 0.0001) was not correlated with changes in energy compensation. Conclusions: This study suggests that exercise improves the accuracy of compensation for previous EI, independent of weight loss. Unexpectedly, and in contrast to GIP and leptin, exercise-induced weight loss had no effect on obestatin or CCK concentrations.
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The Use of Blood Vessel–Derived Stem Cells for Meniscal Regeneration and Repair
Wed, 05/01/2013 - 05:00Purpose: Surgical repairs of tears in the vascular region of the meniscus usually heal better than repairs performed in the avascular region; thus, we hypothesized that this region might possess a richer supply of vascular-derived stem cells than the avascular region. Methods: In this study, we analyzed 6 menisci extracted from aborted human fetuses and 12 human lateral menisci extracted from adult human subjects undergoing total knee arthroplasty. Menisci were immunostained for CD34 (a stem cell marker) and CD146 (a pericyte marker) in situ, whereas other menisci were dissected into two regions (peripheral and inner) and used to isolate meniscus-derived cells by flow cytometry. Cell populations expressing CD34 and CD146 were tested for their multilineage differentiation potentials, including chondrogenic, osteogenic, and adipogenic lineages. Fetal peripheral meniscus cells were transplanted by intracapsular injection into the knee joints of an athymic rat meniscal tear model. Rat menisci were extracted and histologically evaluated after 4 wk posttransplantation. Results: Immunohistochemistry and flow cytometric analyses demonstrated that a higher number of CD34- and CD146-positive cells were found in the peripheral region compared with the inner region. The CD34- and CD146-positive cells isolated from the vascular region of both fetal and adult menisci demonstrated multilineage differentiation capacities and were more potent than cells isolated from the inner (avascular) region. Fetal CD34- and CD146-positive cells transplanted into the athymic rat knee joint were recruited into the meniscal tear sites and contributed to meniscus repair. Conclusions: The vascularized region of the meniscus contains more stem cells than the avascular region. These meniscal-derived stem cells were multipotent and contributed to meniscal regeneration.
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Advances in Exercise, Fitness, and Performance Genomics in 2012
Wed, 05/01/2013 - 05:00ABSTRACT: A small number of excellent articles on exercise genomics issues were published in 2012. A new PYGM knock-in mouse model will provide opportunities to investigate the exercise intolerance and very low activity level of people with McArdle disease. New reports on variants in ACTN3 and ACE have increased the level of uncertainty regarding their true role in skeletal muscle metabolism and strength traits. The evidence continues to accumulate on the positive effects of regular physical activity on body mass index or adiposity in individuals at risk of obesity as assessed by their FTO genotype or by the number of risk alleles they carry at multiple obesity-susceptibility loci. The serum levels of triglycerides and the risk of hypertriglyceridemia were shown to be influenced by the interactions between a single nucleotide polymorphism (SNP) in the NOS3 gene and physical activity level. Allelic variation at nine SNPs was shown to account for the heritable component of the changes in submaximal exercise heart rate induced by the HERITAGE Family Study exercise program. SNPs at the RBPMS, YWHAQ, and CREB1 loci were found to be particularly strong predictors of the changes in submaximal exercise heart rate. The 2012 review ends with comments on the importance of relying more on experimental data, the urgency of identifying panels of genomic predictors of the response to regular exercise and particularly of adverse responses, and the exciting opportunities offered by recent advances in our understanding of the global architecture of the human genome as reported by the Encyclopedia of DNA Elements project.
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Maternal Exercise Improves Insulin Sensitivity in Mature Rat Offspring
Wed, 05/01/2013 - 05:00Purpose: Recent findings have shown that the intrauterine environment can negatively influence long-term insulin sensitivity in the offspring. Here we look at maternal voluntary exercise as an intervention to improve offspring insulin sensitivity and glucose homeostasis. Methods: Female Sprague–Dawley rats were split into sedentary and exercise groups with the exercise cohort having voluntary access to a running wheel in the cage before and during mating, pregnancy, and nursing. Female offspring were weaned into sedentary cages. Glucose tolerance tests and hyperinsulinemic-euglycemic clamp were performed in adult offspring to evaluate glucose regulation and insulin sensitivity. Results: Adult female offspring born to exercised dams had enhanced glucose disposal during glucose tolerance testing (P < 0.05) as well as increased glucose infusion rates (P < 0.01) and whole body glucose turnover rates (P < 0.05) during hyperinsulinemic-euglycemic clamp testing compared with offspring from sedentary dams. Offspring from exercised dams also had decreased insulin levels (P < 0.01) and hepatic glucose production (P < 0.05) during the clamp procedure compared with offspring born to sedentary dams. Offspring from exercised dams had increased glucose uptake in skeletal muscle (P < 0.05) and decreased heart glucose uptake (P < 0.01) compared with offspring from sedentary dams in response to insulin infusion during the clamp procedure. Conclusions: Exercise during pregnancy enhances offspring insulin sensitivity and improves offspring glucose homeostasis. This can decrease offspring susceptibility to insulin-resistant related diseases such as type 2 diabetes mellitus. Maternal exercise could be an easy, short-term, nonpharmacological method of preventing disease in future generations.
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Metabolic Adaptations in the Liver of Born Long-Distance Running Mice
Wed, 05/01/2013 - 05:00Purpose: Long-distance runners have increased needs of energy supply. To unravel genetically based mechanisms required for efficient energy supply, we have analyzed hepatic metabolism of mice characterized by the inborn capacity to perform as long-distance runners. Methods: The mouse model had been established by phenotypic selection for high treadmill performance for 90 generations and was characterized by approximately 3.8-fold higher running capacities (Dummerstorf high Treadmill Performance mouse line [DUhTP]) compared with unselected and also untrained controls (Dummerstorf Control mouse line [DUC]). From 7-wk-old male mice, serum and liver samples were collected and analyzed for messenger RNA, protein, and metabolite levels, respectively. Results: In livers from DUhTP mice, we identified significantly higher messenger RNA transcript levels of peroxisome proliferator–activated receptor delta and higher protein levels of sirtuin-1, acetyl-CoA-synthetase, acetyl-CoA-carboxylase, phosphoenolpyruvate carboxykinase, and glutamate-dehydrogenase, suggesting higher gluconeogenesis and lipogenesis in DUhTP mice. In fact, higher hepatic levels of glycogen and triglycerides as well as higher concentrations of carbohydrate, fatty acid, and cholesterol metabolites were found in DUhTP mice. In parallel, in DUhTP mice, which did not have access to running wheels, a marked hyperlipidemia (cholesterol = 160% ± 8%, triglycerides = 174% ± 14% of controls, respectively), and abdominal obesity (DUhTP = 0.396 ± 0.019 g, DUC = 0.291 ± 0.019 g) were found. Conclusions: From our data, we conclude that the physiological basis of genetically fixed higher endurance-running performance in DUhTP marathon mouse is related to increased hepatic gluconeogenesis and lipogenesis. Expression of sirtuin 1 as well as of gluconeogenic and lipogenic key enzymes may be related to peroxisome proliferator–activated receptor delta. Metabolic adaptations presented in our study represent inborn features of superior endurance-running performance.
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The Antidepressant-like Effect of Physical Activity on a Voluntary Running Wheel
Wed, 05/01/2013 - 05:00Purpose: Physical activity is currently being considered an effective alternative in the treatment of depression. At the preclinical level, the voluntary running wheel is a useful method of increasing physical activity in rodents and induces an antidepressant-like effect in some behavioral paradigms. Methods: This study investigated the effect of physical activity on a voluntary running wheel in mice submitted to the forced swimming test (FST) and tail suspension test, two predictive tests of antidepressant properties. Moreover, the influence of the inhibition of serotonin and noradrenaline synthesis as well as the inhibition of protein kinase A (PKA) and calcium/calmodulin-dependent protein kinase II (CAMK-II) activity by pharmacological agents in the antidepressant-like action of physical activity was investigated. Results: Physical activity on a voluntary running wheel by 21 d produced a reduction in the immobility time in the FST and tail suspension test, without producing alteration on locomotor activity in the open-field test. The antidepressant-like effect in the FST elicited by physical activity lasted for 7 d after removal of the running wheel. The anti-immobility effect of physical activity was prevented by the pretreatment of mice with p-chlorophenylalanine methyl ester (100 mg·kg−1, i.p., once a day, for four consecutive days, inhibitor of serotonin synthesis), α-methyl-p-tyrosine (100 mg·kg−1, i.p., an inhibitor of noradrenaline and dopamine synthesis), H-89 (1 μg per site, i.c.v., a PKA inhibitor), and KN-62 (1 μg per site, i.c.v., a CAMK-II inhibitor). Conclusions: Taken together, these results first suggest that the effect of physical activity on the FST is dependent on either the increase in the bioavailability of monoamines in the synaptic cleft or an activation of intracellular signaling pathways mediated by PKA and CAMK-II.
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Markers of Muscle Damage and Performance Recovery after Exercise in the Heat
Wed, 05/01/2013 - 05:00Purpose: This study aimed to determine whether competitive intermittent exercise in the heat affects recovery, aggravates markers of muscle fiber damage, and delays the recovery of performance and muscle glycogen stores. Methods: Plasma creatine kinase, serum myoglobin, muscle glycogen, and performance parameters (sprint, endurance, and neuromuscular testing) were evaluated in 17 semiprofessional soccer players before, immediately after, and during 48 h of recovery from a match played in 43°C (HOT) and compared with a control match (21°C with similar turf and setup). Results: Muscle temperature was ∼1°C higher (P < 0.001) after the game in HOT compared with control and reached individual values between 39.9°C and 41.1°C. Serum myoglobin levels increased by more than threefold after the matches (P < 0.01), but values were not different in HOT compared with control, and they were similar to baseline values after 24 h of recovery. Creatine kinase was significantly elevated both immediately and 24 h after the matches, but the response after HOT was reduced compared with control. Muscle glycogen responses were similar across trials and remained depressed for more than 48 h after both matches. Sprint performance and voluntary muscle activation were impaired to a similar extent after the matches (sprint by ∼2% and voluntary activation by ∼1.5%; P < 0.05). Both of these performance parameters as well as intermittent endurance capacity (estimated by a Yo-Yo IR1 test) were fully recovered 48 h after both matches. Conclusion: Environmental heat stress does not aggravate the recovery response from competitive intermittent exercise associated with elevated muscle temperatures and markers of muscle damage, delayed resynthesis of muscle glycogen, and impaired postmatch performance.
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Skeletal Muscle Metabolism in Endurance Athletes with Near-Infrared Spectroscopy
Wed, 05/01/2013 - 05:00Purpose: To determine whether near-infrared spectroscopy (NIRS) measurements of muscle mitochondrial function could detect the expected differences between endurance-trained athletes (n = 8) and inactive subjects (n = 8). Methods: Muscle oxygen consumption (mV˙O2) of the vastus lateralis was measured with continuous-wave NIRS using transient arterial occlusions. The recovery rate of mV˙O2 after electrical stimulation was fit to an exponential curve, with the time constant (Tc) used as an index of mitochondrial capacity. Whole-body peak oxygen uptake was determined by indirect calorimetry during a continuous ramp protocol on a cycle ergometer. Results: Whole-body peak oxygen uptake values for endurance-trained and inactive controls were 73.5 ± 9.1 and 33.7 ± 5.9 mL·kg−1·min−1, respectively (P < 0.001). The recovery rates of mV˙O2 after exercise for endurance training were 18.4 ± 3.2 and 18.8 ± 2.5 s, whereas those for inactive controls were 32.4 ± 5.2 and 34.9 ± 5.9 s for the shallow and deep channels, respectively (P < 0.001 for comparison between groups). Resting mV˙O2 was 0.52%·s−1 ± 0.22%·s−1 for endurance athletes and 0.77%·s−1 ± 0.82%·s−1 for inactive controls (P = 0.42). Conclusions: The recovery rates of mV˙O2 after exercise in endurance athletes were almost twofold faster than inactive subjects measured with NIRS, consistent with previous studies using muscle biopsies and magnetic resonance spectroscopy. Our results support the use of NIRS measurements of the recovery of oxygen consumption to assess muscle oxidative capacity.
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Influence of Postexercise Cooling on Muscle Oxygenation and Blood Volume Changes
Wed, 05/01/2013 - 05:00Purpose: The aim of this study was to investigate the effects of postexercise cold water immersion (CWI) on tissue oxygenation and blood volume changes after intense exercise. Methods: Nine physically active men performed 30 min of continuous running (CR) at 70% of their maximal treadmill velocity (Vmax), followed by 10 bouts of intermittent running at Vmax. After exercise, one of the participants’ legs was immersed in a cold water bath (10°C, CWI) to the level of their gluteal fold for 15 min. The contralateral leg remained outside the water bath and served as a control (CON). Vastus lateralis (VL) skin temperature (TskVL), VL oxygenation (tissue oxygenation index [TOI]), and blood volume changes (total hemoglobin [tHb] volume) were monitored continuously throughout exercise and CWI using near-infrared spectroscopy. Results: TskVL, TOI, and tHb were not significantly different between CON and CWI during continuous running and intermittent running, respectively (P > 0.05). In contrast, TskVL was significantly lower in CWI compared with CON throughout immersion, with peak differences occurring at the end of immersion (CON = 35.1 ± 0.6 vs CWI = 16.9°C ± 1.7°C, P < 0.001). tHb was significantly lower during CWI compared with CON at most time points, with peak differences of 20% ± 4% evident at the end of the 15-min immersion (P < 0.01). Likewise, TOI was significantly higher in CWI compared with CON, with peak differences of 2.5% ± 1% evident at the 12th min of immersion (P < 0.05). Conclusions: Postexercise cooling decreased microvascular perfusion and muscle metabolic activity. These findings are consistent with the suggested mechanisms by which CWI is hypothesized to improve local muscle recovery.
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No Effect of 1 or 7 d of Green Tea Extract Ingestion on Fat Oxidation during Exercise
Wed, 05/01/2013 - 05:00Purpose: The aim of this study was to investigate the effects of 1 and 7 d of green tea extract (GTE) ingestion on whole body fat oxidation during moderate-intensity exercise. Methods: Thirty-one men completed two exercise trials (60-min cycle, 50% Wmax). After the baseline trial (day 0), subjects were randomly assigned to one of three conditions involving a week supplementation of the following: 1) 7 d of placebo, 2) 6 d of placebo followed by 1 d of GTE (GTE1), and 3) 7 d of GTE ingestion (GTE7). The morning after the supplementation week, subjects consumed an additional supplement and completed a second exercise trial (day 8). V˙O2 and V˙CO2 measurements were taken during exercise to calculate whole body fat oxidation rates. Blood samples, for analysis of plasma fatty acids (FA), glycerol, and epigallocatechin gallate, were collected at rest and during exercise. Results: On day 8, the plasma kinetics and maximal plasma concentrations of epigallocatechin gallate were similar in the GTE1 and GTE7 group (206 ± 28 and 216 ± 25 ng·mL−1, respectively). One day of GTE ingestion did not affect markers of lipolysis during the exercise bout. Seven days of GTE ingestion significantly increased plasma glycerol during exercise (P = 0.045) and plasma FA during exercise (P = 0.020) as well as at rest (P = 0.046). However, fat oxidation did not change in any of the groups. Conclusions: There was no effect of 1 d of GTE ingestion on markers of lipolysis or fat oxidation during exercise. Seven days of GTE ingestion increased lipolysis, indicated by increased plasma FA and glycerol concentrations, but did not result in significant changes in fat oxidation.
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Association Analysis of ACE and ACTN3 in Elite Caucasian and East Asian Swimmers
Wed, 05/01/2013 - 05:00Purpose: Polymorphic variation in the angiotensin-converting enzyme (ACE) and α-actinin-3 (ACTN3) genes has been reported to be associated with endurance and/or power-related human performance. Our aim was to investigate whether polymorphisms in ACE and ACTN3 are associated with elite swimmer status in Caucasian and East Asian populations. Methods: ACE I/D and ACTN3 R577X genotyping was carried out for 200 elite Caucasian swimmers from European, Commonwealth, Russian, and American cohorts (short and middle distance, ≤400 m, n = 130; long distance, >400 m, n = 70) and 326 elite Japanese and Taiwanese swimmers (short distance, ≤100 m, n = 166; middle distance, 200–400 m, n = 160). Genetic associations were evaluated by logistic regression and other tests accommodating multiple testing adjustment. Results: ACE I/D was associated with swimmer status in Caucasians, with the D allele being overrepresented in short-and-middle-distance swimmers under both additive and I-allele-dominant models (permutation test P = 0.003 and P = 0.0005, respectively). ACE I/D was also associated with swimmer status in East Asians. In this group, however, the I allele was overrepresented in the short-distance swimmer group (permutation test P = 0.041 and P = 0.0098 under the additive and the D-allele-dominant models, respectively). ACTN3 R577X was not significantly associated with swimmer status in either Caucasians or East Asians. Conclusions: ACE I/D associations were observed in these elite swimmer cohorts, with different risk alleles responsible for the associations in swimmers of different ethnicities. The functional ACTN3 R577X polymorphism did not show any significant association with elite swimmer status, despite numerous previous reports of associations with “power/sprint” performance in other sports.
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Physical Activity and Cardiovascular Disease in African Americans in Atherosclerosis Risk in Communities
Wed, 05/01/2013 - 05:00Purpose: Although there is substantial evidence that physical activity reduces a person’s risk of cardiovascular disease (CVD), few of these studies have included African Americans. The studies that have included African Americans offer inconclusive evidence on the association, and none studied heart failure separately. We used data from the Atherosclerosis Risk in Communities study cohort to examine, in African Americans, the association of physical activity with the incidence of CVD and its major components—stroke, heart failure, and CHD. Methods: Participants age 45–64 yr (3707 African Americans and, for comparison, 10,018 Caucasians) had physical activity assessed via questionnaire in 1987 and were followed for incident CVD (n = 1039) through 2008. Results: After adjustment for potential confounders, physical activity was inversely related to CVD, heart failure, and CHD incidence in both races (P values for trend <0.0001), and with stroke in African Americans. Hazard ratios (95% confidence intervals) for CVD for each higher physical activity category were similar by race: 1.0, 0.65 (0.56–0.75), and 0.59 (0.49–0.71) for African Americans and 1.0, 0.74 (0.66–0.83), and 0.67 (0.59–0.75) for Caucasians (P value for interaction = 0.38). Conclusions: Our findings reinforce recommendations that regular physical activity is important for CVD risk reduction in African Americans as well as Caucasians and support the idea that some physical activity is better than none.
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Sports Injuries in Paralympic Track and Field Athletes with Visual Impairment
Wed, 05/01/2013 - 05:00Purpose: The aims of this study were to determine the epidemiology, nature, and pattern of sports injuries in Brazilian Paralympic track and field athletes with visual impairment and to assess differences between visual classes and sex. Methods: Forty visually impaired elite Paralympic athletes participated in this study (28 males and 12 females). All athletes competed in International Paralympic competitions between 2004 and 2008. According to the visual classification, 14 athletes were T/F11, 15 were T/F12, and 11 were T/F13. A standardized report form was used to collect injury data during five competitions. Results: Thirty-one athletes reported 77 sports injuries, with a prevalence of 78%, a clinical incidence of 1.93 injuries per athlete, and an incidence rate of 0.39 injuries per athlete per competition. Overuse injuries accounted for 82% and traumatic injuries 18% (P < 0.05). Small variations in the prevalence and clinical incidence of injury between sexes and visual classes were observed, but these were not statistically different (P > 0.05). The highest distribution of injury was in the lower limbs (87%), followed by spine (12%) and upper limbs (1%). The body regions most affected were the thighs (33.8%), lower legs (16.9%), and knees (9.1%). The most frequent diagnoses were spasms (26%), tendinopathies (23.4%), and strains (13%). Conclusions: Elite visually impaired track and field Paralympic athletes present a pattern of overuse injuries predominantly affecting the lower limbs, particularly the thighs, lower legs, and knees. These injuries are associated with tendinopathies, muscle spasms, and strains. There were no apparent differences in injury characteristics between visual classes or sex.
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Steps per Day, Peak Cadence, Body Mass Index, and Age in Community-Dwelling Older Adults
Wed, 05/01/2013 - 05:00Purpose: The relationships between demographic and anthropometric indices and older adults’ quantity and quality of ambulatory activity are uncertain. We examined the relationship between accelerometer-determined steps per day (quantity) and peak 30-min cadence (quality; mean steps per minute recorded for the 30 highest, but not necessarily consecutive, minutes in a day) in community-dwelling older adults relative to sex, age, and body mass index (BMI). Methods: Minute-by-minute accelerometer-determined step data for 5.8 ± 0.9 d were available for 100 women and 43 men (58–92 yr, BMI = 26.6 ± 4.2 kg·m−2). Sex-specific Spearman correlations compared steps per day with peak 30-min cadence and both to age and BMI. Partial correlations were computed controlling for 1) age, 2) BMI, 3) steps per day and age, or 4) steps per day and BMI. Significance was set at P < 0.05. Results: Participants averaged 5605 ± 2588 steps per day with a peak 30-min cadence of 63.6 ± 24.6 steps per minute (mean ± SD). Correlations between these two variables were r = 0.883 (women) and r = 0.820 (men). Steps per day and peak 30-min cadence were significantly correlated with age (r = −0.442 and r = −0.327, respectively) and BMI (r = −0.248 and r = −0.286, respectively) in women. For men, steps per day and peak 30-min cadence were only significantly related to age (r = −0.665 and r = −0.381, respectively). Controlling for steps per day weakened all relationships with peak 30-min cadence to a point of nonsignificance with one exception: the partial correlation of age with peak 30-min cadence was weakened but remained significant (r = 0.335) after controlling for steps per day and BMI in men. Conclusions: The usefulness of peak 30-min cadence beyond steps per day is not apparent, at least in terms of sex, age, and BMI, and needs to be evaluated in larger and more diverse samples and against other parameters of interest, including those more theoretically linked to intensity of effort.
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Effect of Gradient on Cycling Gross Efficiency and Technique
Wed, 05/01/2013 - 05:00Purpose: The purpose of this study was to determine the effect of gradient on cycling gross efficiency and pedaling technique. Methods: Eighteen trained cyclists were tested for efficiency, index of pedal force effectiveness (IFE), distribution of power production during the pedal revolution (dead center size [DC]), and timing and level of muscle activity of eight leg muscles. Cycling was performed on a treadmill at gradients of 0% (level), 4%, and 8%, each at three different cadences (60, 75, and 90 rev·min−1). Results: Efficiency was significantly decreased at a gradient of 8% compared with both 0% and 4% (P < 0.05). The relationship between cadence and efficiency was not changed by gradient (P > 0.05). At a gradient of 8%, there was a larger IFE between 45° and 225° and larger DC, compared with 0% and 4% (P < 0.05). The onset of muscle activity for vastus lateralis, vastus medialis, gastrocnemius lateralis, and gastrocnemius medialis occurred earlier with increasing gradient (all P < 0.05), whereas none of the muscles showed a change in offset (P > 0.05). Uphill cycling increased the overall muscle activity level (P < 0.05), mainly induced by increased calf muscle activity. Conclusions: These results suggest that uphill cycling decreases cycling gross efficiency and is associated with changes in pedaling technique.
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Predicting the Patellar Tendon Force Generated When Landing from a Jump
Wed, 05/01/2013 - 05:00Purpose: Although high patellar tendon loading is believed to be the primary causative factor for patellar tendinopathy, research investigating factors that affect patellar tendon loading during landing is scarce. Therefore, the purpose of this study was to identify whether factors previously associated with the development of patellar tendinopathy, and selected variables characterizing landing technique, could predict patellar tendon loading incurred by volleyball players when landing from a jump. Methods: Ten highly skilled male, 20 skilled male, and 20 skilled female volleyball players performed a lateral stop–jump movement. Sex, skill level, quadriceps strength, quadriceps extensibility, and trunk moment of inertia were recorded. Landing kinematics (250 Hz) and kinetics (1500 Hz) were collected, and peak patellar tendon force and patellar tendon force loading rate were calculated. Backward multiple regression analyses identified which risk factors or landing technique variables were predictors of patellar tendon loading. Results: Multiple regression analyses were able to estimate and predict 52% (F4,49 = 14.258, P < 0.001) and 70% (F4,49 = 29.329, P < 0.001) of the peak patellar tendon force and the patellar tendon force loading rate variance, respectively. The present study revealed that male volleyball players with greater quadriceps strength, who displayed increased ankle dorsiflexion velocity and trunk flexion velocity during landing, were predicted to incur higher patellar tendon loading. Conclusions: As frequent application of high patellar tendon loading has previously been identified as a causative factor for developing patellar tendinopathy, interventions designed to decrease ankle dorsiflexion velocity and trunk flexion velocity at landing, particularly in male players with strong quadriceps muscles, may be effective in reducing patellar tendon loading and, in turn, patellar tendinopathy prevalence in this population.
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Influence of Relative Hip and Knee Extensor Muscle Strength on Landing Biomechanics
Wed, 05/01/2013 - 05:00Purpose: This study aimed to determine whether the tendency of women to exhibit higher knee extensor moments relative to hip extensor moments during the deceleration phase of landing can be explained by the relative strength of the knee and hip extensors. Methods: Forty recreationally active individuals participated in this study (20 men and 20 women). The maximum isometric strength of the knee extensors and hip extensors was assessed using a load cell and custom testing setup. Lower extremity kinematics and kinetics were collected during a double-leg drop-jump task. Results: When compared with men, women demonstrated a significantly higher knee–hip extensor moment ratio during the deceleration phase of landing (1.42 ± 0.6 vs 1.12 ± 0.3, P < 0.001). In addition, the knee–hip extensor isometric strength ratio was significantly higher in women compared with men (1.01 ± 0.2 vs 0.89 ± 0.2, P < 0.001). The Pearson partial correlation (controlling for sex) revealed a significant positive association between the knee–hip extensor isometric strength ratio and the knee–hip extensor moment ratio (r = 0.41, P = 0.005). Conclusion: The tendency of women to exhibit higher knee extensor moments relative to hip extensor moments may be explained, in part, by the relative strength of the hip and knee extensors.
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Knee Biomechanics during a Jump-Cut Maneuver: Effects of Sex and ACL Surgery
Wed, 05/01/2013 - 05:00Purpose: The purpose of this study was to compare kinetic and knee kinematic measurements from male and female anterior cruciate ligament (ACL)–intact (ACLINT) and ACL-reconstructed (ACLREC) subjects during a jump-cut maneuver using biplanar videoradiography. Methods: Twenty subjects were recruited; 10 ACLINT (5 men and 5 women) and 10 ACLREC (4 men and 6 women, 5 yr postsurgery). Each subject performed a jump-cut maneuver by landing on a single leg and performing a 45° side-step cut. Ground reaction force (GRF) was measured by a force plate and expressed relative to body weight. Six-degree-of-freedom knee kinematics were determined from a biplanar videoradiography system and an optical motion capture system. Results: ACLINT female subjects landed with a larger peak vertical GRF (P < 0.001) compared with ACLINT male subjects. ACLINT subjects landed with a larger peak vertical GRF (P ≤ 0.036) compared with ACLREC subjects. Regardless of ACL reconstruction status, female subjects underwent less knee flexion angle excursion (P = 0.002) and had an increased average rate of anterior tibial translation (0.05%·ms−1 ± 0.01%·ms−1, P = 0.037) after contact compared with male subjects. Furthermore, ACLREC subjects had a lower rate of anterior tibial translation compared with ACLINT subjects (0.05%·ms−1 ± 0.01%·ms−1, P = 0.035). Finally, no striking differences were observed in other knee motion parameters. Conclusion: Women permit a smaller amount of knee flexion angle excursion during a jump-cut maneuver, resulting in a larger peak vertical GRF and increased rate of anterior tibial translation. Notably, ACLREC subjects also perform the jump cut maneuver with lower GRF than ACLINT subjects 5 yr postsurgery. This study proposes a causal sequence whereby increased landing stiffness (larger peak vertical GRF combined with less knee flexion angle excursion) leads to an increased rate of anterior tibial translation while performing a jump-cut maneuver.
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Modified Kaatsu Training: Adaptations and Subject Perceptions
Wed, 05/01/2013 - 05:00Purpose: Although Kaatsu training involves low training loads, high perceived exertion and pain scores suggest that potential benefits may be offset by poor adherence or tolerance, particularly if applied in untrained or clinical populations. The purpose of this study was to investigate muscle adaptations, perceived exertion ratings, perceived sensations, and exercise adherence to a modified Kaatsu training protocol involving upper arm exercise. Methods: Forty subjects ages 18–30 yr were assigned to exercise (EX) or nonexercise control (CON) groups. The EX group performed three sets of 15 repetitions of unilateral biceps and triceps exercises, three times per week for 8 wk while wearing a pneumatic cuff to restrict blood flow on one arm (CUFF) and nothing on the other (NCUFF). The CON group did not exercise but wore the cuff on one arm for a comparable amount of time. Strength, girth, tomography scans along with RPE, and sensations during workouts were assessed. Perceived exertion and sensations were assessed during workouts using visual analog scales. Results: Biceps curl and triceps extension strength along with arm size increased during the 8-wk period when compared with the CON group. Compliance was 85.4% and 97% for the EX and CON groups, respectively. EX subjects completed 85.4% of their workouts, whereas controls attended 90.4% of their sessions. The prominent sensations reported in the CUFF arm were pressure and aching. Conclusions: The Kaatsu training used in this study yielded moderate exertion ratings and low-pressure sensations, increased muscle size and strength, and was well tolerated, thereby lending support to Kaatsu training’s potential as a training modality for untrained or clinical populations.
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Comment on “Estimating Activity and Sedentary Behavior from an Accelerometer on the Hip and Wrist”
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