While it has been well established that an acute stretching program can inhibit maximal muscle performance, the amount of stretching needed to produce the deleterious response is unknown. Therefore ...this study examined the dose-response relationship between acute stretching and strength inhibition. Eighteen college students performed a one repetition maximum (1-RM) test of knee-flexion following 0, 1, 2, 3, 4, 5, or 6 30-s bouts of hamstring stretching held at the limit of toleration. All seven dose variations were done by each subject, with each variation done on a separate day. One week separated each test, and the order of the stretch variations was balanced across the seven testing days. Stretching significantly (p < .05) reduced 1-RM after one 30-s stretch (5.4%), and continued to decrease 1-RM up to and including six 30-s stretches (12.4%). A single 30-s stretch, if held at the limit of toleration, is sufficient to cause an inhibition in a person's 1-RM. Additional bouts of stretching will further decrease the 1-RM, suggesting that multiple mechanisms may be involved in stretch-induced strength inhibition.
Ensuring internal validity is the key procedure when planning the study design. Numerous systematic reviews have demonstrated that considerations for internal validity do not receive adequate ...attention in the primary research in sport sciences. Therefore, the purpose of this study was to review methodological procedures in current literature where the effects of resistance training on strength, speed, and endurance performance in athletes were analyzed. A computer-based literature searches of SPORTDiscus, Scopus, Medline, and Web of Science was conducted. The internal validity of individual studies was assessed using the PEDro scale. Peer-reviewed studies were accepted only if they met all the following eligibility criteria: (a) healthy male and female athletes between the ages of 18-65 years; (b) training program based on resistance exercises; (c) training program lasted for at least 4 weeks or 12 training sessions, with at least two sessions per week; (d) the study reported maximum strength, speed, or endurance outcomes; and (e) systematic reviews, cohort studies, case-control studies, cross-sectional studies were excluded. Of the 6,516 articles identified, 133 studies were selected for rating by the PEDro scale. Sixty-eight percent of the included studies used random allocation to groups, but only one reported concealed allocation. Baseline data are presented in almost 69% of the studies. Thirty-eight percent of studies demonstrated adequate follow-up of participants. The plan to follow the intention-to-treat or stating that all participants received training intervention or control conditions as allocated were reported in only 1.5% of studies. The procedure of blinding of assessors was also satisfied in only 1.5% of the studies. The current study highlights the gaps in designing and reporting research in the field of strength and conditioning. Randomization, blinding of assessors, reporting of attrition, and intention-to-treat analysis should be more fully addressed to reduce threats to internal validity in primary research.
This study investigated the effects of ballistic resistance training and strength training on muscle fiber composition, peak force (PF), maximal strength, and peak power (PP). Fourteen males (age = ...21.3 +/- 2.9, body mass = 77.8 +/- 10.1 kg) with 3 months of resistance training experience completed the study. Subjects were tested pre and post for their squat one-repetition maximum (1RM) and PP in the jump squat (JS). Peak force and rate of force development (RFD) were tested during an isometric midthigh pull. Muscle biopsies were obtained from the vastus lateralis for analysis of muscle fiber type expression. Subjects were matched for strength and then randomly selected into either training (T) or control (C) groups. Group T performed 8 weeks of JS training using a periodized program with loading between 26 and 48% of 1RM, 3 days per week. Group T showed significant improvement in PP from 4088.9 +/- 520.6 to 5737.6 +/- 651.8 W. Rate of force development improved significantly in group T from 12687.5 +/- 4644.0 to 25343.8 +/- 12614.4 N x s(-1). PV improved significantly from 1.59 +/- 0.41 to 2.11 +/- 0.75 m x s(-1). No changes occurred in PF, 1RM, or muscle fiber type expression for group T. No changes occurred in any variables in group C. The results of this study indicate that using ballistic resistance exercise is an effective method for increasing PP and RFD independently of changes in maximum strength (1RM, PF), and those increases are a result of factors other than changes in muscle fiber type expression.
This study investigated kinematic and kinetic variable changes in the power snatch (PS) after 4 weeks of training and the use of summary feedback. Twenty-four collegiate football players participated ...as subjects in this study. The subjects were pretested for their 1-repetition maximum (1RM) and were separated into feedback (FG; n = 12) and control (CG; n = 12) groups. The FG was provided with augmented feedback (AF) during power snatch training sessions, which took place 3 times per week for 4 weeks. The AF is defined as information that is received in addition to what is naturally available. Variables measured include peak force (PF), peak power (PP), and several kinematic variables at 50, 70, and 90% of the subjects' pre-1RM. The PF was improved at 50% 1RM from 567 +/- 202 to 769 +/- 230 N, at 70% from 725 +/- 186 to 890 +/- 199 N, and at 90% from 822 +/- 197 to 1008 +/- 201 N in the FG (p <or= 0.05). The PP was increased at 50% 1RM from 2061 +/- 562 to 2538 +/- 498 W, at 70% from 2321 +/- 743 to 2754 +/- 629 W, and at 90% from 2076 +/- 437 to 2491 +/- 526 W in the FG (p <or= 0.05). Variables with respect to bar path kinematics improved significantly. No improvements in kinetics or kinematics were noted in the CG. These results indicate that both kinematic and kinetic variables improve through training and AF. Practitioners wishing to improve weightlifting performance should attempt to use evidence-based AF.
Pompe disease is an autosomal recessive disorder of glycogen metabolism caused by a deficiency of the lysosomal enzyme acid α-glucosidase (GAA). It presents at any age, with variable rates of ...progression ranging from a rapidly progressive course, often fatal by one-year of age, to a more slowly, but nevertheless relentlessly progressive course, resulting in significant morbidity and premature mortality. In infants, early initiation of enzyme replacement therapy is needed to gain the maximum therapeutic benefit, underscoring the need for early diagnosis. Several new methods for measuring GAA activity have been developed. The Pompe Disease Diagnostic Working Group met to review data generated using the new methods, and to establish a consensus regarding the application of the methods for the laboratory diagnosis of Pompe disease. Skin fibroblasts and muscle biopsy have traditionally been the samples of choice for measuring GAA activity. However, new methods using blood samples are rapidly becoming adopted because of their speed and convenience. Measuring GAA activity in blood samples should be performed under acidic conditions (pH 3.8–4.0), using up to 2
mM of the synthetic substrate 4-methylumbelliferyl-α-
d-glucoside or glycogen (50
mg/mL), in the presence of acarbose (3–9
μM) to inhibit the isoenzyme maltase–glucoamylase. The activity of a reference enzyme should also be measured to confirm the quality of the sample. A second test should be done to support the diagnosis of Pompe disease until a program for external quality assurance and proficiency testing of the enzymatic diagnosis in blood is established.
The purpose of this study was to compare session rating of perceived exertion for different resistance training techniques in the squat exercise. These techniques included traditional resistance ...training, super slow, and maximal power training. Fourteen college-age women (Mean ± SD; age = 22 ± 3 years; height = 1.68 ± 0. 07 m) completed three experimental trials in a randomized crossover design. The traditional resistance training protocol consisted of 6 sets of 6 repetitions of squats using 80% of 1-RM. The super slow protocol consisted of 6 sets of 6 repetitions using 55% of 1-RM. The maximal power protocol consisted of 6 sets of 6 repetitions using 30% of 1-RM. Rating of perceived exertion (RPE) measures were obtained following each set using Borg's CR-10 scale. In addition, a session RPE value was obtained 30 minutes following each exercise session. When comparing average RPE and session RPE, no significant difference was found. However, power training had significantly lower (p < 0.05) average and session RPE (4.50 ± 1.9 and 4.5 ± 2.1) compared to both super slow training (7.81 ± 1.75 and 7.43 ± 1.73) and traditional training (7.33 ± 1.52 and 7.13 ± 1.73). The results indicate that session RPE values are not significantly different from the more traditional methods of measuring RPE during exercise bouts. It does appear that the resistance training mode that is used results in differences in perceived exertion that does not relate directly to the loading that is used. Using session RPE provides practitioners with the same information about perceived exertion as the traditional RPE measures. Taking a single measure following a training session would appear to be much easier than using multiple measures of RPE throughout a resistance training workout. However, practitioners should also be aware that the RPE does not directly relate to the relative intensity used and appears to be dependent on the mode of resistance exercise that is used. Key PointsThe present study showed that session RPE values are not significantly different from the more traditional methods of measuring RPE during exercise bouts.Power training had significantly lower average and session RPE compared to both super slow training and traditional trainingIt does appear that the resistance training mode that is used results in differences in perceived exertion that does not relate directly to the loading that is used.
Glc1Man9GlcNAc2-PP-dolichyl α1,3-glucosyltransferase (ALG8). ...far, the only patient has been described with a relatively mild clinical picture. According to topology predictions, T47 is located in ...a long peptide motif in the first luminal loop of ALG8, a region which shows conservation among the dolP-Man and dolP-Glc dependent mannosyl- and glucosyltransferases. 26 Position 275 (glycine) is located in the cytoplasmic loop between the transmembrane domains 6 and 7 and is also conserved between ALG6 and ALG8 of different species but not in other mannosyl- or glucosyltransferases. 26 Despite these differences in position and conservation, no significant difference has been observed in the effect of the mutations on the ALG8 function.
Previous research has demonstrated the importance of isometric maximal strength (PF) and rate of force development (RFD) in a variety of athletic populations including track cyclists and track and ...field athletes. Among coaches and sports scientists there is a lack of agreement regarding how much strength is required for optimal performance in most sports. The purpose of this study was to examine relationships between measures of PF, RFD and one repetition maximum (1RM) strength with other variables that might contribute to successful performance in collegiate wrestlers. Eight men (M = 20.0, SD = 0.4 years; Height M = 1.68, SD = 0. 13 m; Mass M = 78.0, SD = 4.2 kg) who were Division III college wrestlers participated in this study. They were tested for PF using the isometric mid thigh pull exercise. Explosive strength was measured as RFD from the isometric force-time curve. The 1RM for the squat, bench press and power clean exercises were determined as a measure of dynamic strength. Vertical jump height was measured to determine explosive muscular power. The wrestlers also ranked themselves and the coaches of the team also provided a ranking of the athletes. Correlations between the variables were calculated using the Pearson product moment method. Results indicated strong correlations between measures of PF and 1RM (r = 0.73 - 0.97). The correlations were very strong between the power clean 1RM and PF (r = 0.97) and squat 1RM and PF (r = 0.96). There were no other significant correlations with other variables apart from a strong correlation between RFD and coaches ranking (r = 0.62). Findings suggest that isometric mid thigh pull test does correlate well with 1RM testing in college wrestlers. RFD does not appear to be as important in college wrestlers. The isometric mid thigh pull provides a quick and efficient method for assessing isometric strength in athletes. This measure also provides a strong indication of dynamic performance in this population. The lack of strong correlations with other performance variables may be a result of the unique metabolic demands of wrestling. Key PointsIn Division III collegiate wrestlers the isometric mid thigh pull test correlates well with 1RM testing.Rate of Force Development does not appear to be as important in college wrestlers.The lack of strong correlations with other performance variables may be a result of the unique metabolic demands of wrestling.
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