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Biomedical subjects

D T Kirkendall

Publications and source records attributed to D T Kirkendall.

At least 19 recordsLinked to original sources
PubMed2005

Injury history as a risk factor for incident injury in youth soccer.

OBJECTIVES: To determine if athletes with a self reported history of previous injury have a higher incident injury rate than athletes without a self reported injury history. METHODS: A prospective cohort study of Classic League soccer players playing at the level under 12 through under 18. Injury history forms were mailed to all registering Classic League soccer players in the North Carolina Youth Soccer Association during 1997-2000 (n = 7000); 1483 (19%) returned the baseline questionnaire and were followed up for injuries. RESULTS: There were 5139 player-seasons of follow up and an estimated 171 957 athlete-exposures. More than half self reported an injury history (59.7%). Overall, the unadjusted incidence rate was 4.6 (95% confidence interval (CI) 4.3 to 4.9) incident injuries per 1000 athlete-exposures. Multivariate generalised Poisson regression modelling indicated that players with one previous injury had a twofold greater risk of incident injury (IRR = 2.6; 95% CI 2.0 to 3.3), and those with two or more previous injuries had a threefold greater risk of incident injury (IRR = 3.0; 95% CI 2.3 to 3.8) compared with athletes with no previous injuries. CONCLUSIONS: Injury history was associated with an increased injury rate. This suggests that, even in these youth soccer players, those with an injury history may be at higher risk.

Adolescent↗
PubMed2001

A comparison of knee joint motion patterns between men and women in selected athletic tasks.

BACKGROUND: Women have higher non-contact anterior cruciate ligament injury rate than men do in sport activities. Non-contact anterior cruciate ligament injuries frequently occur in sports requiring cutting tasks. Alternated motor control strategies have identified as a potential risk factor for the non-contact anterior cruciate ligament injuries. The purpose of this study was to compare the patterns of knee kinematics and electromyographic activities in running, side-cutting, and cross-cutting between men and women recreational athletes. METHODS: Three-dimensional kinematic data of the knee and electromyographic data of selected muscles across the knee joint were collected for 11 men and 9 women recreational athletes in running, side-cutting, and cross-cutting. Regression analyses with dummy variables for comparison of knee motion patterns between men and women. RESULTS: Women tend to have less knee flexion angles, more knee valgus angles, greater quadriceps activation, and lower hamstring activation in comparison to men during the stance phase of each of the three athletic tasks. Literatures suggest these alternated knee motion patterns of women tend to increase the load on the anterior cruciate ligament. CONCLUSION: Women on average may have certain motor control strategies that may alter their knee motion patterns. Women's altered knee motion patterns may tend to increase the load on the anterior cruciate ligament in the selected athletic tasks, which may contribute to the increased anterior cruciate ligament injury rate among women. RELEVANCE: Non-contact anterior cruciate ligament injuries frequently occur in sports. Altered motor control strategies and lower extremity motion patterns are likely to play an important role in non-contact anterior cruciate ligament injuries. Non-contact anterior cruciate ligament injuries may be prevented by correcting altered motor control strategies and associated lower extremity motion patterns through certain training programs.

Electromyography↗
PubMed2001

Heading and head injuries in soccer.

In the world of sports, soccer is unique because of the purposeful use of the unprotected head for controlling and advancing the ball. This skill obviously places the player at risk of head injury and the game does carry some risk. Head injury can be a result of contact of the head with another head (or other body parts), ground, goal post, other unknown objects or even the ball. Such impacts can lead to contusions, fractures, eye injuries, concussions or even, in rare cases, death. Coaches, players, parents and physicians are rightly concerned about the risk of head injury in soccer. Current research shows that selected soccer players have some degree of cognitive dysfunction. It is important to determine the reasons behind such deficits. Purposeful heading has been blamed, but a closer look at the studies that focus on heading has revealed methodological concerns that question the validity of blaming purposeful heading of the ball. The player's history and age (did they play when the ball was leather and could absorb significant amounts of water), alcohol intake, drug intake, learning disabilities, concussion definition and control group use/composition are all factors that cloud the ability to blame purposeful heading. What does seem clear is that a player's history of concussive episodes is a more likely explanation for cognitive deficits. While it is likely that the subconcussive impact of purposeful heading is a doubtful factor in the noted deficits, it is unknown whether multiple subconcussive impacts might have some lingering effects. In addition, it is unknown whether the noted deficits have any affect on daily life. Proper instruction in the technique is critical because if the ball contacts an unprepared head (as in accidental head-ball contacts), the potential for serious injury is possible. To further our understanding of the relationship of heading, head injury and cognitive deficits, we need to: learn more about the actual impact of a ball on the head, verify the exposure to heading at all ages and competitive levels, determine stable estimates of concussive injury rates across the soccer spectrum, conduct prospective longitudinal studies on soccer players focusing on exposure, injury and cognition, and determine the minimum safe age to begin instruction on the skill of heading. Only then will we be able to speak with some authority on the issue of heading and head injuries in soccer.

Biomechanical Phenomena↗
PubMed2000

The anterior cruciate ligament enigma. Injury mechanisms and prevention.

The reasons for the higher frequency of anterior cruciate ligament injuries in women are largely conjecture. These injuries may result from direct contact or, more frequently, from no direct contact to the knee during activities that most athletes consider routine to their sport. This implies that there are intrinsic factors that lead to anterior cruciate ligament rupture. For the anterior cruciate ligament to tear, there must be excess anterior tibial translation or rotation of the femur on the tibia. In the former case, the tibia can move anteriorly during quadriceps activation that is not counterbalanced by hamstring activation. Patients describe their injury as occurring when landing, stopping, or when planting to change directions. The knee typically was near full extension. Mechanically, the angle of the patellar tendon and tibial shaft increases as the knee approaches full extension. This gives a mechanical advantage to the quadriceps. During cutting maneuvers, athletes tend to cut with a knee near extension (0 degree-20 degrees) when the quadriceps are active and the hamstrings are neither very active nor at a knee flexion angle that offers much of a mechanical advantage. In performing cutting and landing maneuvers, women tend to perform the activities more erect; that is, with their knee and hips closer to extension. One possible factor to help reduce the frequency of anterior cruciate ligament injuries in women may be in proper instruction for performing cutting and landing maneuvers which will lower their center of gravity thereby denying the quadriceps the opportunity to shift the tibia anteriorly.

Anterior Cruciate Ligament Injuries↗
PubMed2000

Shoulder muscle activation during aquatic and dry land exercises in nonimpaired subjects.

STUDY DESIGN: Randomized, single blind experimental design using electromyography to measure shoulder muscle activation in nonimpaired subjects. OBJECTIVES: To compare the muscle activation of rotator cuff and shoulder synergists during rehabilitation exercises performed in water or on dry land. BACKGROUND: Early motion is critical to restoration of normal shoulder function. Aquatic therapy has been promoted as a method for increasing range of motion while minimizing stress on the shoulder. METHODS AND MEASURES: The integrated electromyography amplitude of 6 muscles of the shoulder girdle was examined on the nondominant shoulders of 6 subjects (supraspinatus, infraspinatus, and subscapularis, anterior, middle, and posterior deltoids). Each subject performed elevation (0 degree to 90 degrees) in the scapular plane with neutral rotation on land and in water at 3 different speeds of elevation (30 degrees/s, 45 degrees/s, and 90 degrees/s). The mean percentage of the maximal voluntary contraction was determined for each of the 3 test speeds on land and in water. Comparisons between water and dry land were made with a repeated measures analysis of variance. RESULTS: For all 6 muscles tested, muscle activation during the 30 degrees/s test speed and all muscles tested at the 45 degrees/s test speed was significantly less when performed in water versus when performed on land. For example, electromyography activation of the supraspinatus muscle was 16.68% of a maximal voluntary contraction when elevation at was performed at 30 degrees/s on dry land versus 3.93% when performed in water. CONCLUSION: These data suggest that shoulder elevation in the water at slower speeds resulted in a significantly lower activation of the rotator cuff and synergistic muscles. This decreased muscle activation during aquatic physical therapy allows for earlier active motion in the postoperative period without compromising patient safety.

Adult↗
PubMed1999

Electromyographic analysis and energy expenditure of harness supported treadmill walking: implications for knee rehabilitation.

Harness supported treadmill ambulation has been recommended for patients as a way of decreasing loads on the healing tissues, conserving energy and reducing pain. We quantified muscle activation levels around the knee and metabolic responses during harness supported treadmill walking. Ten healthy recreational athletes (age 28.9+/-7.8 years) walked on the treadmill (1.34 m/s) for 5 min each at full weight bearing (FWB), 20 and 40% body weight support (BWS). Electromyography (EMG) was monitored for the vastus lateralis, vastus medialis, rectus femoris, biceps femoris, medial hamstrings and the gastrocnemius. Oxygen consumption was collected by open circuit spirometry and the heart rate was collected by a heartwatch. A statistically significant reduction in EMG was found at 40% BWS for the quadriceps. Oxygen consumption decreased by 6% (20% BWS) and by 12% (40% BWS) from FWB (P<0.05). The heart rate was unchanged. BWS ambulation reduces energy cost, but does not significantly alter muscle activation, except for the quadriceps at 40% BWS.

Adult↗
PubMed1998

Fluid and electrolyte replacement in soccer.

Soccer can be played under a wide range of environmental conditions. Traditionally, fluid replacement is limited during the game, but in reality, there are numerous opportunities for fluid ingestion during a match. Many of the recommendations on fluid replenishment have been directed at continuous exercise, and application of those suggestions can be applied to an intermittent sport like soccer.

Drinking↗
PubMed1997

Function and biomechanics of tendons.

Tendon is a highly organized connective tissue joining muscle to bone, capable of resisting high tensile forces while transmitting forces from muscle to bone. The dense, regularly arranged collagenous tissue is made up of fibers, cells of various shapes and ground substance. The mechanical and physiological characteristics of collagen (nearly 85% of the dry weight of tendon) dictate the qualities of tendon. In addition, tendon is flexible so that it can bend at joints, as well as acting as a damping tissue to absorb shock and limit potential damage to muscle (1). Tendon also shows a degree of extensibility. If the strain used to stretch a tendon could be recovered, a beneficial elastic effect would be achieved. Muscles lengthen and shorten in a cyclical manner. During the lengthening period, elastic energy can be stored and used as elastic recoil. For example, the Achilles tendon is stretched late in the stance phase as the triceps surae muscles contract and the ankle dorsiflexes. Prior to plantarflexion, muscle activation ceases and stored energy helps to initiate planter flexion.

Adrenal Cortex Hormones↗
PubMed1997

Technical considerations for electromyographic research on the shoulder.

This study compared 2 methods of indwelling bipolar electrode insertion. One method used a single needle for the insertion of both wire leads, and the second method used 2 needles for the independent insertion of both leads at a specified interdetection distance. Simultaneous electromyography recordings from the 2 different electrode configurations were made during the activation of nonfatigued supraspinatus and infraspinatus muscles from 10 healthy subjects. Subjects performed 6 different isometric contractions at 3 different levels of force (100%, 60%, and 30% effort). In this study, the bipolar electrode configuration using 2 hypodermic needles for placement of the 2 leads produced superior electromyography recordings than did the configuration using a single needle for the wire lead insertion. The separated bipolar electrodes produced a significantly higher amplitude electromyography signal with less intersubject variability and greater partial correlation with force. This study suggests an alternative method of bipolar wire electrode placement that results in improved signal characteristics and decreased variability of signal acquisition. A standardization of wire electromyography examination of the shoulder that improves signal characteristics and acquisition ultimately will lead to more accurate results with greater clinical use and validity.

Action Potentials↗
PubMed1996

Optimal normalization tests for shoulder muscle activation: an electromyographic study.

To accurately compare electromyographic data from different muscles and different subjects, it is necessary to normalize the integrated data obtained from each muscle. The purpose of this study was to identify the manual muscle testing positions that elicit maximal neural activation (integrated electromyography) of three rotator cuff muscles (supraspinatus, infraspinatus, and subscapularis) and five shoulder synergists (pectoralis major, latissimus dorsi, and anterior, middle, and posterior deltoids). The electromyographic activity of these eight muscles was examined in the nondominant shoulders of nine subjects. Indwelling wire electrodes (supraspinatus, infraspinatus, and subscapularis) and surface adhesive electrodes (pectoralis major, latissimus dorsi, and anterior, middle, and posterior deltoids) were placed. Each subject performed a series of 27 isometric contractions, and optimal tests (maximal neural activation) were identified for each muscle. Four tests were identified that resulted in the maximal neural activation of all eight shoulder muscles: 90 degrees of scapular elevation with -45 degrees of humeral rotation for the supraspinatus, anterior deltoid, and middle deltoid: external rotation at 90 degrees of scapular elevation and -45 degrees of humeral rotation for the infraspinatus and posterior deltoid: internal rotation at 90 degrees of scapular elevation and neutral humeral rotation for the subscapularis and latissimus dorsi: and internal rotation at 0 degree of elevation and neutral rotation for the pectoralis major. These results identify four standard testing positions that will provide reference values for normalization of maximal voluntary contraction for the eight muscles of the shoulder examined in this study. Standardization of these test positions offers normalization guidelines that can be used in future dynamic electromyography studies of the shoulder.

Adult↗
PubMed1996

A 20-yr longitudinal study of Olympic oarsmen.

Nine 1972 silver-medalist oarsmen were studied before the Olympic Games and 10 and 20 yr later. Peak power, metabolic responses, and heart rate were recorded during rowing ergometry; blood lactate was measured following exercise. The skinfold equation yielded percent body fat. The average change (multiple analysis of variance) among measurements from 1972 to 1992 was 37.5 +/- 3% (P < 0.01). Average changes between 1972 and 1982 and between 1982 and 1992 were similar, 17 and 18%, respectively (P < 0.01). The most significant change between 1972 and 1992 was decreased peak blood lactate (106%). Decreases in peak power, VE, and VO2 (ml.kg-1.min-1) were all similar, approximately 40%, and were significant. Body fat increased (from 12.3 to 15.6%), and absolute VO2 and relative VO2 (lean body mass) decreased 30% (P < 0.01). Only body weight, heart rate, and O2 pulse showed smaller changes, but these changes were still significant (P < 0.05). Relative peak VO2 decreased from 65.5 to 46.8 ml.kg-1.min-1 from 1972 to 1992 and at a rate of 10%.decade-1. The most significant changes between 1972 and 1982 were increases in percent body fat (from 12.3 to 16.3%) and decreases in VO2 values (P < 0.01). There was less change in body fat between 1982 and 1992, but lactate significantly decreased (P < 0.01), as did peak power and absolute and relative VO2 and VE. Although fitness levels in former elite oarsmen decreased each decade, these declines were somewhat arrested by regular aerobic training. Body fat increased and metabolic capacity decreased rapidly during the first decade, whereas anaerobic capacity decreased more significantly in the second decade. Anaerobic capacity diminished at a significantly greater rate than aerobic capacity, probably as a result of the aging process and emphasis on aerobic training in post-competitive years.

Adult↗
PubMed1993

A comparison of temperature rise in human calf muscles following applications of underwater and topical gel ultrasound.

For ultrasound to be effective, a conducting medium must be placed between the soundhead and the skin. Little research has been performed to test whether or not these mediums actually work. The purpose of this study was to compare the effect of tap water immersion and ultrasound gel conducting mediums on tissue temperature rise in the human leg. A 23-gauge hypodermic needle microprobe was inserted 3 cm deep into the medial portion of the gastrocnemius muscle of 20 subjects. Each subject participated in two random order treatments using tap water immersion and topical gel conducting mediums. Each treatment consisted of continuous ultrasound delivered topically at 1.5 W/cm2 for 10 minutes. During both treatments, the soundhead was moved at a speed of 4 cm per second, and the temperature was recorded every 30 seconds. A significant difference was found between the two treatment methods [t(19) = 9.18, p < .001]. The topical gel increased tissue temperature 4.8 degrees C, whereas the underwater treatment increased tissue temperature only 2.1 degrees C. Therefore, at a tissue depth of 3 cm, ultrasound gel is a better conducting medium than water. Also, the authors discovered that it took nearly 8 minutes for the temperature to reach therapeutic levels during the gel technique. These findings should be of clinical significance to clinicians who regularly use ultrasound.

Adult↗
PubMed1993

Effects of nutrition on performance in soccer.

The majority of research on nutrition and physical performance centers around continuous endurance exercise. That appropriate food intake can influence endurance performance is widely recognized. Considering that games in general and soccer in particular enjoy an enormous amount of participation, it should come as no surprise that nutritional influences on soccer performance has been studied. The literature shows that soccer is a glycogen-depleting activity and that work volume and rate are influenced by level of muscle glycogen. The dietary habits of soccer players do not appear to contain optimal carbohydrate intake given the varied, and sometimes minimal, amount of time between games. Nutritional assessment and counseling, if necessary, are suggested to afford the player adequate glycogen stores to work at the rate and volume demanded by the game.

Glycogen↗
PubMed1990

Mechanisms of peripheral fatigue.

Fatigue can be defined as the failure to maintain an expected power output. This is often an antecedent to some sports-related injury. It is important for those involved in physical performance to be familiar with the variety of mechanisms which can lead to fatigue. All too often, a single factor is described as the cause of fatigue when actually fatigue may be a combination of factors that contribute to the sequence of events that results in decreased performance. It may be suggested that every step in the chain of events that leads to voluntary contraction of skeletal muscle could be a culprit in fatigue. Peripheral sites and processes include the motor neuron, neuromuscular junction, sarcolemmal membrane, excitation-contraction coupling, accumulation of metabolites, or depletion of fuels. Physical training is frequently designed to delay the onset of fatigue. The actual mechanism(s) add to the specificity concept, that is, a "specificity of fatigue". To the performer, the end result is the same, the inability to maintain his or her expected level of performance or power output.

Action Potentials↗
PubMed1989

The effects of anabolic steroids and strength training on the human immune response.

The immune response was assessed in 13 competitive bodybuilders self-administering anabolic-androgenic steroids and ten competitive bodybuilders not administering these drugs. Laboratory assessment included the number and relative distribution of T-cells, T-helper/inducer cells, T-cytotoxic/suppressor cells, activated T-cells, lymphocyte transformation to the mitogens, pokeweed mitogen (PWM), phytohemagglutinin (PHA), Concanavalin-A (CON-A), Staphylococcus aureus Cowan strain I (SAC), serum immunoglobulins, and natural killer (NK) activity. There were no significant differences in T-cell subsets among steroid users and non-users, but lymphocyte transformation studies revealed that the anabolic-androgenic steroid-using group had enhanced proliferative ability to the B-cell mitogen, SAC, in comparison to non-bodybuilding controls. NK activity was significantly (P less than 0.05) augmented in the anabolic-androgenic steroid users but not in the non-using bodybuilders. Serum immunoglobulin levels, in particular IgA, were significantly (P less than 0.017) lower in the steroid-using group. Four of 13 steroid users and three of eight non-steroid-using bodybuilders had detectable antinuclear antibodies. These studies indicate that 1) anabolic-androgenic steroid use as practiced by contemporary athletes is a potent modulator of immune responsiveness and 2) autoantibodies are prevalent in strength-trained men even in the absence of anabolic steroid use.

Anabolic Agents↗
PubMed1986

Mechanical jumping power in athletes.

The Wingate cycle ergometer test is a widely used test of sustained muscular power. A limitation of the test is the lack of development and retrieval of stored elastic energy due to a lack of an eccentric phase. To measure mechanical power output of the entire stretch-shortening cycle, the test of Bosco et al (1983) was administered to 119 male athletes in 7 different activities during their pre-participation evaluations. The sports tested were indoor soccer, American football and ballet (professionals), outdoor soccer, basketball and wrestling (collegiate) and amateur bobsled. Results showed the overall average power output to be 20.37 W.kg-1 for the 60s reciprocal jumping test. Ballet dancers generated significantly less mechanical power than indoor soccer, basketball and bobsled athletes, while wrestlers generated significantly less power than indoor soccer and basketball athletes (all p less than 0.05). No other between-sport differences were seen. A subset of indoor soccer players (n = 10) were retested after 4 months of training. Power improved from 20.8 to 24.3 W.kg-1 (p less than 0.05). While between sport differences were limited, training differences in one subset of athletes were readily identified.

Adult↗
PubMed1985

Physiologic aspects of gymnastics.

It should be evident from this discussion that there has been little research on gymnastics specifically. A great deal of applied work on the physiology of gymnastics needs to be explored. The bulk of research recently has been related to skill performance (biomechanics). The limited data indicated that the gymnast has the expected low aerobic capacity, due to the short time factor in competition. They are quite lean and muscular and extremely flexible about the hip and shoulders. Training for gymnastics should emphasize activities specifically related to the routine. Various methods can be used to reduce the fatigue that develops throughout the routine and improve performance of the activity. Supplemental strength training should be emphasized using multiple joint exercises.

Body Composition↗