Biomedical subjects

Michael R Sitler

Publications and source records attributed to Michael R Sitler.

10 recordsLinked to original sources

PubMed2006

Gender comparisons of dynamic restraint and motor skill in children.

OBJECTIVES: To assess differences in neuromuscular dynamic restraint between high-skilled and low-skilled prepubescent girls and boys. To determine the contribution of sport experience and physical characteristics to motor skill. SUBJECTS: Nineteen girls and 17 boys (8.89-9.40 y) participated. INTERVENTION: Isometric hamstring and quadriceps muscle strength was assessed. Subjects performed 3 landing trials for measurement of preparatory EMG and vertical leg stiffness. Motor skill was assessed through analysis of 12 fundamental tasks. Sport experience was reported as hours per week and total years in organized and nonorganized activity. OUTCOME MEASURES: Dynamic restraint variables of isometric strength, preparatory EMG activity, and vertical leg stiffness were measured between groups. The contributions of time in sport, type of sport, and physical characteristics on skill were analyzed. RESULTS: No significant gender or skill differences were found in quadriceps strength (P = 0.73), hamstring strength (P = 0.96), hamstring-to-quadriceps ratio (P = 0.71), or vertical leg stiffness (P = 0.38). Low-skilled children exhibited significantly greater (47.8%) preparatory hamstring-quadriceps coactivation than high-skilled subjects (P = 0.03). Participation in organized and nonorganized sport accounted for 29% of the variance in motor skill. CONCLUSIONS: Neuromuscular differences between genders were not observed, but dynamic restraint EMG measures differed between skill levels. The factors predisposing females to noncontact injuries may develop prepuberty to postpuberty from a combination of variables. Greater coactivation in the low-skilled group appears consistent with immature feedforward neuromuscular control strategies. These unrefined motor skills are less economical, may compromise dynamic restraint, and appear partially determined by sport experience.

Athletic Injuries↗

PubMed2005

Gender differences in head-neck segment dynamic stabilization during head acceleration.

PURPOSE: Recent epidemiological research has revealed that gender differences exist in concussion incidence but no study has investigated why females may be at greater risk of concussion. Our purpose was to determine whether gender differences existed in head-neck segment kinematic and neuromuscular control variables responses to an external force application with and without neck muscle preactivation. METHODS: Forty (20 females and 20 males) physically active volunteers participated in the study. The independent variables were gender, force application (known vs unknown), and force direction (forced flexion vs forced extension). The dependent variables were kinematic and EMG variables, head-neck segment stiffness, and head-neck segment flexor and extensor isometric strength. Statistical analyses consisted of multiple multivariate and univariate analyses of variance, follow-up univariate analyses of variance, and t-tests (P < or = 0.05). RESULTS: Gender differences existed in head-neck segment dynamic stabilization during head angular acceleration. Females exhibited significantly greater head-neck segment peak angular acceleration (50%) and displacement (39%) than males despite initiating muscle activity significantly earlier (SCM only) and using a greater percentage of their maximum head-neck segment muscle activity (79% peak activity and 117% muscle activity area). The head-neck segment angular acceleration differences may be because females exhibited significantly less isometric strength (49%), neck girth (30%), and head mass (43%), resulting in lower levels of head-neck segment stiffness (29%). CONCLUSION: For our subject demographic, the results revealed gender differences in head-neck segment dynamic stabilization during head acceleration in response to an external force application. Females exhibited significantly greater head-neck segment peak angular acceleration and displacement than males despite initiating muscle activity earlier (SCM only) and using a greater percentage of their maximum head-neck segment muscle activity.

Acceleration↗

PubMed2005

Effectiveness of prophylactic hyperextension elbow braces on limiting active and passive elbow extension prephysiological and postphysiological loading.

STUDY DESIGN: Experimental 3-factor design with repeated measures on all factors. OBJECTIVES: The purpose of this study was to determine the effectiveness of 3 prophylactic hyperextension elbow braces on limiting active and passive elbow extension before and after exercise. BACKGROUND: Prophylactic hyperextension elbow braces are used to protect the joint against excessive extension, but their effectiveness for this purpose has not been determined. METHODS AND MATERIALS: Twenty Division I intercollegiate football players (mean +/- SD age, 20.2 +/- 1.3 years; mean +/- SD height, 184.4 +/- 9.9 cm, mean +/- SD mass, 102.9 +/- 22.0 kg) completed all phases of the study. The Breg Functional Elbow Brace, PRO 470 Kendall Elbow Brace, and DonJoy Elbow Guard were tested both actively and passively before and after an isokinetic exercise session on a Biodex Multi-Joint Testing and Exercise Dynamometer. For all tests, the braces were set at a 30 degrees flexion limit angle. The exercise session consisted of 1 set of reciprocal elbow extension and flexion at an angular velocity of 360 degrees/s, totaling 1627 J of work. RESULTS: None of the braces limited elbow extension to the 30 degrees flexion limit. However, all of the braces were successful in preventing the elbow from reaching the vulnerable position of hyperextension. The Breg Functional Elbow Brace was the most effective for limiting elbow extension near its set angle, followed by the DonJoy Elbow Guard, and the PRO 470 Kendall Elbow Brace across all test conditions. CONCLUSION: The braces' effectiveness to limit motion is enhanced when limits are set higher than the desired angle of the protected motion.

Adult↗

PubMed2002

Head Position and Football Equipment Influence Cervical Spinal-Cord Space During Immobilization.

OBJECTIVE: To assess the effect of head position and football equipment (ie, helmet and shoulder pads) on cervical spinal cord space in individuals lying supine on a spine board. DESIGN AND SETTING: The independent variables were head position (0-cm, 2-cm, and 4-cm occiput elevation with no helmet and shoulder pads and with helmet and shoulder pads) and cervical spine level (C3, C4, C5, C6, and C7). The 3 dependent variables were sagittal space available for the cord (SAC) (mm), sagittal spinal-cord diameter (mm), and cervical-thoracic angle ( degrees ), determined via magnetic resonance imaging. SUBJECTS: Twelve men (age = 24.3 +/- 2.1 years; height = 181.1 +/- 5.7 cm; weight = 93.9 +/- 3.6 kg). MEASUREMENTS: Sagittal space available for the cord was determined by subtracting the sagittal spinal-cord diameter from the corresponding sagittal spinal-canal diameter. The spinal-canal diameter was measured as the shortest distance from the vertebral body to the spinolaminar line at each of the spinal levels. Each measurement was taken 3 times, and the 3 measurements were averaged. RESULTS: Sagittal space available for the cord was significantly greater (P <.01) for 0-cm (mean = 5.50 mm) than for 2-cm (mean = 4.86 mm) and 4-cm (mean = 5.07 mm) occiput elevation. SAC was also significantly greater (P <.01) for the equipment condition (mean = 5.34 mm) than for the 2-cm and 4-cm elevation levels. No significant difference (P =.093) in SAC existed between 0-cm elevation and the equipment condition. CONCLUSIONS: The helmet and shoulder pads should be left on during spine-board immobilization of the injured football player. Similarly, during spine-board immobilization of an individual without football helmet and shoulder pads, the head should be maintained at 0 cm of occiput elevation. Sagittal spinal-cord space is optimized in both of these conditions.

Journal Article↗

PubMed2002

Cervical Spine Stenosis Measures in Normal Subjects.

OBJECTIVE: To compare 2 methods of determining cervical spinal stenosis (Torg ratio, space available for the cord [SAC]); determine which of the components of the Torg ratio and the SAC account for more of the variability in the measures; and present standardized SAC values for normal subjects using magnetic resonance imaging (MRI). DESIGN AND SETTING: The research design consisted of a posttest-only, comparison-group design. The independent variable was method of measurement (Torg ratio and SAC). The dependent variables were Torg ratio and SAC scores. SUBJECTS: Fourteen men (age = 24.4 +/- 2.5 years, height = 181.0 +/- 5.8 cm, weight = 90 +/- 13.5 kg) participated in this study. The C3 to C7 vertebrae were examined in each subject (n = 70). MEASUREMENTS: The Torg ratio was determined by dividing the sagittal spinal-canal diameter by the corresponding sagittal vertebral-body diameter. The SAC was determined by subtracting the sagittal spinal-cord diameter from the corresponding sagittal spinal-canal diameter. The Torg ratio and SAC were measured in millimeters. RESULTS: The SAC ranged from 2.5 to 10.4 mm and was greatest at C7 in 71% (10 of 14) of the subjects. The SAC was least at C3 or C5 in 71% (10 of 14) of the subjects. A Pearson product moment correlation revealed a significant relationship between the Torg ratio and SAC (r =.53, P <.01). Regression analyses revealed the vertebral body (r (2) =.58) accounted for more variability in the Torg ratio than the spinal canal (r (2) =.48). Also, the spinal canal (r (2) =.66) accounted for more variability in the SAC than the spinal cord (r (2) =.23). CONCLUSIONS: The SAC measure relies more on the spinal canal compared with the Torg ratio and, therefore, may be a more effective indicator of spinal stenosis. This is relevant clinically because neurologic injury related to stenosis is a function of the spinal canal and the spinal cord (not the vertebral body). Further research must be done, however, to validate the SAC measure.

Journal Article↗

PubMed2002

Temporal Pattern of the Repeated Bout Effect of Eccentric Exercise on Delayed-Onset Muscle Soreness.

OBJECTIVE: To determine the temporal pattern of the repeated bout effect of eccentric exercise on perceived pain and muscular tenderness associated with delayed-onset muscle soreness (DOMS). DESIGN AND SETTING: Subjects completed 2 identical eccentric exercise bouts separated by 6, 7, 8, or 9 weeks. The experiment was conducted in a biokinetics research laboratory. SUBJECTS: Sixteen male and 15 female untrained subjects (age = 24.59 +/- 4.42 years, height = 171.71 +/- 7.81 cm, weight = 73.00 +/- 11.20 kg). MEASUREMENTS: Two physiologic characteristics of DOMS were measured immediately before and 0, 24, 48, and 72 hours after each eccentric exercise bout. Perceived pain was measured using a visual analog scale (VAS), and muscular tenderness was measured using a punctate tenderness gauge (PTG). RESULTS: Two 4 x 2 x 5 (group x bout x time) analyses of variance with repeated measures on the bout and time factors were performed on the VAS and PTG data. Significant (P <.05) main effects were found for group, bout, and time for the VAS and the PTG data. No significant interactions were detected. Post hoc analysis revealed significantly less perceived pain for the 9-week group than the 8-week group. The 7-week group had significantly less and the 8-week group had significantly more muscular tenderness than any other group. Perceived pain and muscular tenderness were significantly less after exercise bout 2 than after exercise bout 1. All subjects had significantly less perceived pain and muscular tenderness pre-exercise than 0 and 24 hours after the eccentric exercise bouts. CONCLUSIONS: An effective prophylaxis for perceived pain and muscular tenderness associated with DOMS is the performance of an eccentric exercise bout 6 to 9 weeks before a similar exercise bout.

Journal Article↗

PubMedDate not supplied

Effect of a prophylactic brace on wrist and ulnocarpal joint biomechanics in a cadaveric model.

BACKGROUND: Wrist pain from repetitive dorsiflexion and compression during pommel horse exercises is common among male gymnasts. PURPOSE: To determine the biomechanical effects of a prophylactic wrist brace on the wrist and ulnocarpal joints during mechanical loading in a cadaveric model. HYPOTHESIS: The lateral wedge of the palmar pad of the brace will compensate for positive ulnar variance, distributing contact forces more evenly across the radioulnar carpal joint. STUDY DESIGN: Controlled laboratory study. METHODS: Six male and six female fixed cadaveric forearm-wrist specimens were subjected to a 32.13-kg compressive load applied through the long axis of the pronated forearm with a dorsiflexed wrist in contact with a support surface. Wrist joint dorsiflexion angle and ulnocarpal joint intraarticular peak pressure were assessed under three brace conditions: Ezy ProBrace with and without palmar pad and a nonbraced control. RESULTS: Wrist joint dorsiflexion angle was significantly reduced by the Ezy ProBrace with and without the palmar pad. However, ulnocarpal joint intraarticular peak pressure was reduced only by the brace with pad. CONCLUSION: Prevention of pathologic wrist changes requires intervention in pressure attenuation, which was achieved with the Ezy ProBrace with palmar pad. CLINICAL RELEVANCE: This brace may decrease the cumulative effects of repetitive stress of pommel horse exercise training.

Aged↗

PubMedDate not supplied

Dehydration and symptoms of delayed-onset muscle soreness in hyperthermic males.

CONTEXT: Exercise in the heat produces cellular conditions that may leave skeletal muscle susceptible to exercise-induced microdamage. Delayed-onset muscle soreness (DOMS) is a clinical model of contraction-induced skeletal muscle injury. OBJECTIVE: To determine whether thermoregulation during exercise heat stress adversely affects muscle injury and the accompanying DOMS. DESIGN: Randomized group test-retest design. SETTING: Laboratory. PATIENTS OR OTHER PARTICIPANTS: Ten healthy male volunteers were randomly assigned to either the euhydration/hyperthermic or dehydration/hyperthermic group. INTERVENTION(S): Participants were randomly assigned to treadmill walking in a hot, humid environmental chamber (40 degrees C and 75% relative humidity) with either oral rehydration (euhydration/hyperthermic) or fluid restriction (dehydration/hyperthermic). Immediately after heat exposure and while hyperthermic, participants performed an eccentrically biased downhill run to induce DOMS. MAIN OUTCOME MEASURE(S): We measured DOMS characteristics pre-exercise and at 0.5, 24, 48, 72, and 96 hours postexercise. RESULTS: Treadmill exercise and exposure to the hot ambient environment elicited a 0.9% body mass loss for the euhydrated/ hyperthermic (mean rectal temperature after 60 minutes of heat-stress trial = 38.2 +/- 0.4 degrees C) and 3.3% body mass loss for the dehydrated/hyperthermic participants (mean rectal temperature after 60 minutes of heat-stress trial = 38.1 +/- 0.4 degrees C). Quadriceps perceived pain was significantly higher (F(5,40) = 18.717, P <or= .001) than baseline at 24 and 48 hours postexercise, following the classic pattern of DOMS. Overall lower extremity perceived pain was significantly higher for the dehydration/hyperthermia group than the euhydration/hyperthermia group (F(1,8) = 6.713, P = .032). Punctate tenderness of the vastus lateralis for the dehydration/hyperthermic group was 6.9% higher (F(5,40) = 4.462, P = .003) than for the euhydration/ hyperthermic group. No clinically important findings were revealed for passive range of motion for knee flexion. For both groups, quadriceps isometric strength (F(5,40) = 12.924, P <or= .001) was 17.5% and 20.0% lower at 0.5 hours postexercise than at 72 and 96 hours postexercise, respectively. Further, quadriceps isometric strength remained 10.5% reduced at 24 hours postexercise compared with 96 hours postexercise. CONCLUSIONS: Skeletal muscle microdamage, indirectly evidenced by DOMS, was exacerbated in hyperthermic participants dehydrated by exercise in a hot ambient environment. Individuals performing novel exercise, particularly with a significant eccentric component, should use caution when training in a hot, humid environment and implement frequent rest and rehydration breaks.

Journal Article↗

PubMedDate not supplied

Resistance training and head-neck segment dynamic stabilization in male and female collegiate soccer players.

CONTEXT: Cervical resistance training has been purported to aid in reducing the severity of brain injuries in athletes. OBJECTIVE: To determine the effect of an 8-week resistance-training program on head-neck segment dynamic stabilization in male and female collegiate soccer players. DESIGN: Pretest and posttest control group design. SETTING: University research laboratory and fitness center. PATIENTS OR OTHER PARTICIPANTS: Thirty-six National Collegiate Athletic Association Division I collegiate soccer players (17 men, 19 women). INTERVENTION(S): The resistance training group underwent an 8-week cervical resistance training program that consisted of 3 sets of 10 repetitions of neck flexion and extension at 55% to 70% of their 10-repetition maximum 2 times a week. Participants in the control group performed no cervical resistance exercises. MAIN OUTCOME MEASURE(S): Head-neck segment kinematics and stiffness, electromyographic activity of the upper trapezius and sternocleidomastoid muscles during force application to the head, and neck flexor and extensor isometric strength. RESULTS: No kinematic, electromyographic, or stiffness training effects were seen. The posttest resistance training group isometric neck flexor strength was 15% greater than the pretest measurement. Isometric neck extensor strength in the female resistance training group was 22.5% greater at the posttest than at the pretest. Women's neck girth increased 3.4% over time regardless of training group level. Women exhibited 7% less head-neck segment length and 26% less head-neck segment mass than men. CONCLUSIONS: Despite increases in isometric strength and girth, the 8-week isotonic cervical resistance training did not enhance head-neck segment dynamic stabilization during force application in collegiate soccer players. Future researchers should examine the effect of head-neck segment training protocols that include traditional and neuromuscular activities (eg, plyometrics) with the focus of reducing head acceleration on force application.

Journal Article↗

PubMedDate not supplied

Dehydration and symptoms of delayed-onset muscle soreness in normothermic men.

CONTEXT: A dehydrated individual who performs eccentric exercise may exacerbate skeletal muscle damage, leading to structural, contractile, and enzymatic protein denaturation, in addition to the myofiber and connective damage resulting from the eccentric muscle tension. OBJECTIVE: To identify the effects of dehydration on 5 physiologic characteristics of delayed-onset muscle soreness (DOMS) in normothermic men after an eccentric exercise perturbation. DESIGN: Randomized group test-retest design. SETTING: Laboratory. PATIENTS OR OTHER PARTICIPANTS: Ten healthy male volunteers randomly assigned to either a euhydration (age = 26.2 +/- 4.9 years, height = 174.1 +/- 6.0 cm, mass = 86.5 +/- 15.3 kg) or dehydration (age = 25.8 +/- 2.2 years, height = 177.2 +/- 3.1 cm, mass = 84.4 +/- 3.8 kg) group. INTERVENTION(S): Subjects performed treadmill walking for 45 minutes in either a thermoneutral (euhydration) or a hot, humid (dehydration) environment. After a rest period to allow for return to the normothermic condition, DOMS was induced with a 45-minute downhill run. MAIN OUTCOME MEASURES: We assessed 5 physiologic characteristics of DOMS before and at intervals after the eccentric exercise. The characteristics were perceived pain of the bilateral quadriceps and overall body, bilateral punctate tenderness of the superficial quadriceps muscles, bilateral knee-flexion passive range of motion, bilateral thigh circumference, and bilateral isometric quadriceps muscle strength. Thermoregulatory and cardiovascular measures were obtained to monitor participants' heat load during exercise. RESULTS: The experimental protocol produced a 0.9% increase in body mass of the euhydration group and a significant 2.7% decrease in body mass of the dehydration group. The downhill-running exercise perturbation induced DOMS in both the euhydrated and dehydrated participants, based on increased bilateral quadriceps and overall body perceived pain and punctate tenderness of the bilateral vastus medialis muscle. The signs and symptoms of DOMS after an eccentric exercise perturbation were not exacerbated by moderate dehydration of 2.7% body mass after rest and return to the normothermic condition. CONCLUSIONS: Significantly dehydrated participants who rested and returned to a normothermic condition did not experience increased characteristics of DOMS.

Journal Article↗