William E. Prentice

Warming-Up and Stretching for Improved Physical Performance and Prevention of Sports-Related Injuries

SummaryCompetitive and recreational athletes typically perform warm-up and stretching activities to prepare for more strenuous exercise. These preliminary activities are used to enhance physical performance and to prevent sports-related injuries.Warm-up techniques are primarily used to increase body temperature and are classified in 3 major categories: (a) passive warm-up — increases temperature by some external means; (b) general warm-up — increases temperature by nonspecific body movements; and (c) specific warm-up — increases temperature using similar body parts that will be used in the subsequent, more strenuous activity. The best of these appears to be specific warm-up because this method provides a rehearsal of the activity or event. The intensity and duration of warm-up must be individualised according to the athlete’s physical capabilities and in consideration of environmental factors which may alter the temperature response.The majority of the benefits of warm-up are related to temperature-dependent physiological processes. An elevation in body temperature produces an increase in the dissociation of oxygen from haemoglobin and myoglobin, a lowering of the activation energy rates of metabolic chemical reactions, an increase in muscle blood flow, a reduction in muscle viscosity, an increase in the sensitivity of nerve receptors, and an increase in the speed of nervous impulses. Warm-up also appears to reduce the incidence and likelihood of sports-related musculoskeletal injuries.Improving flexibility through stretching is another important preparatory activity that has been advocated to improve physical performance. Maintaining good flexibility also aids in the prevention of injuries to the musculoskeletal system. Flexibility is defined as the range of motion possible around a specific joint or a series of articulations and is usually classified as either static or dynamic. Static flexibility refers to the degree to which a joint can be passively moved to the end-points in the range of motion. Dynamic flexibility refers to the degree which a joint can be moved as a result of a muscle contraction and may therefore not be a good indicator of stiffness or looseness of a joint.There are 3 basic categories of stretching techniques: (a) ballistic — which makes use of repetitive bouncing movements; (b) static — which stretches the muscle to the point of slight muscle discomfort and is held for an extended period; and (c) proprioceptive neuromuscular facilitation — which uses alternating contractions and stretching of the muscles. Each of these stretching methods is based on the neurophysiological phenomenon involving the stretch reflex. The muscle spindle and Golgi tendon organ are receptors sensitive to changes in muscle length and tension and are activated during stretching. Because ballistic, static, and proprioceptive neuromuscular facilitation stretching techniques produce different responses from the stretch reflex, the relative effectiveness of these stretching methods also varies.Studies comparing the effectiveness of the various stretching techniques have been confusing and contradictory. However, the majority of the information on this topic tends to support the use of proprioceptive neuromuscular facilitation techniques for providing the best improvements in flexibility.

The effects of an exercise intervention on forward head and rounded shoulder postures in elite swimmers

Objectives To examine the correction of posture, increase in strength and decrease in shoulder pain and dysfunction in varsity swimmers. Design and Setting Randomised clinical trial. Participants Twenty-eight National Collegiate Athletic Association division I varsity swimmers. Measurements Two testing sessions were conducted before and after an 8-week time period. Posture, strength and shoulder pain and function were assessed. Forward head angle was measured using a digital inclinometer, forward head translation was measured using a ruler and total scapular distance was measured with unmarked string. Average and peak values (N) of strength were measured with the hand-held dynamometer. The intervention subjects then participated in an 8-week exercise training programme to correct posture. The procedures were then repeated in the post-test. Results Significant group by time interactions (p<0.05) were found in forward head angle and forward shoulder translation indicating a decrease in forward head angle and forward shoulder translation. Significant main effects for time (p<0.05) were found in strength measures for all muscle groups indicating increased strength for shoulder girdle muscles tested. Conclusions The exercise intervention was successful at decreasing forward head and rounded shoulder postures in elite swimmers. This study supports the theoretical basis for clinical rehabilitation of posture and the shoulder.

Muscle activation during side-step cutting maneuvers in male and female soccer athletes.

CONTEXT Female soccer athletes are at greater risk of anterior cruciate ligament (ACL) injury than males. Sex differences in muscle activation may contribute to the increased incidence of ACL injuries in female soccer athletes. OBJECTIVE To examine sex differences in lower extremity muscle activation between male and female soccer athletes at the National Collegiate Athletic Association Division I level during 2 side-step cutting maneuvers. DESIGN Cross-sectional with 1 between-subjects factor (sex) and 2 within-subjects factors (cutting task and phase of contact). SETTING Sports medicine research laboratory. PATIENTS OR OTHER PARTICIPANTS Twenty males (age = 19.4 +/- 1.4 years, height = 176.5 +/- 5.5 cm, mass = 74.6 +/- 6.0 kg) and 20 females (age = 19.8 +/- 1.1 years, height = 165.7 +/- 4.3 cm, mass = 62.2 +/- 7.2 kg). INTERVENTION(S) In a single testing session, participants performed the running-approach side-step cut and the box-jump side-step cut tasks. MAIN OUTCOME MEASURE(S) Surface electromyographic activity of the rectus femoris, vastus lateralis, medial hamstrings, lateral hamstrings, gluteus medius, and gluteus maximus was recorded for each subject. Separate mixed-model, repeated-measures analysis of variance tests were used to compare the dependent variables across sex during the preparatory and loading contact phases of each cutting task. RESULTS Females displayed greater vastus lateralis activity and quadriceps to hamstrings coactivation ratios during the preparatory and loading phases, as well as greater gluteus medius activation during the preparatory phase only. No significant differences were noted between the sexes for muscle activation in the other muscles analyzed during each task. CONCLUSIONS The quadriceps-dominant muscle activation pattern observed in recreationally active females is also present in female soccer athletes at the Division I level when compared with similarly trained male soccer athletes. The relationship between increased quadriceps activation and greater incidence of noncontact ACL injury in female soccer athletes versus males requires further study.

Dehydration and Performance on Clinical Concussion Measures in Collegiate Wrestlers

CONTEXT The effects of dehydration induced by wrestling-related weight-cutting tactics on clinical concussion outcomes, such as neurocognitive function, balance performance, and symptoms, have not been adequately studied. OBJECTIVE To evaluate the effects of dehydration on the outcome of clinical concussion measures in National Collegiate Athletic Association Division I collegiate wrestlers. DESIGN Repeated-measures design. SETTING Clinical research laboratory. PATIENTS OR OTHER PARTICIPANTS Thirty-two Division I healthy collegiate male wrestlers (age = 20.0 ± 1.4 years; height = 175.0 ± 7.5 cm; baseline mass = 79.2 ± 12.6 kg). INTERVENTION(S) Participants completed preseason concussion baseline testing in early September. Weight and urine samples were also collected at this time. All participants reported to prewrestling practice and postwrestling practice for the same test battery and protocol in mid-October. They had begun practicing weight-cutting tactics a day before prepractice and postpractice testing. Differences between these measures permitted us to evaluate how dehydration and weight-cutting tactics affected concussion measures. MAIN OUTCOME MEASURES Sport Concussion Assessment Tool 2 (SCAT2), Balance Error Scoring System, Graded Symptom Checklist, and Simple Reaction Time scores. The Simple Reaction Time was measured using the Automated Neuropsychological Assessment Metrics. RESULTS The SCAT2 measurements were lower at prepractice (P = .002) and postpractice (P < .001) when compared with baseline. The BESS error scores were higher at postpractice when compared with baseline (P = .015). The GSC severity scores were higher at prepractice (P = .011) and postpractice (P < .001) than at baseline and at postpractice when than at prepractice (P = .003). The number of Graded Symptom Checklist symptoms reported was also higher at prepractice (P = .036) and postpractice (P < .001) when compared with baseline, and at postpractice when compared with prepractice (P = .003). CONCLUSIONS Our results suggest that it is important for wrestlers to be evaluated in a euhydrated state to ensure that dehydration is not influencing the outcome of the clinical measures.

The influence of hip strength on gluteal activity and lower extremity kinematics

The effects of hip muscle strength and activation on anterior cruciate ligament injury biomechanics, particularly knee valgus loading, have been reported in isolation and with equivocal results. However, the combination of these factors influences joint biomechanics. This investigation evaluated the influence of hip strength on gluteal activation and knee valgus motion. Maximal isometric hip abduction (ABD) and external rotation (ER) contractions were used to define High and Low strength groups. Knee kinematics and gluteus maximus (GMax) and medius (GMed) EMG amplitudes obtained during landing were compared between High and Low strength groups after controlling for the potential confounding influence of sex. Knee valgus motion did not differ between the High and Low hip ABD and ER strength groups. However, the Low ABD and ER strength groups displayed greater GMed and GMax EMG amplitudes, respectively, compared to the High strength groups. These findings suggest that weaker individuals compensate for a lack of force production via heightened neural drive. As such, hip muscle strength influences knee valgus motion indirectly by determining neural drive requirements.

Scapular Bracing and Alteration of Posture and Muscle Activity in Overhead Athletes With Poor Posture

CONTEXT Overhead athletes commonly have poor posture. Commercial braces are used to improve posture and function, but few researchers have examined the effects of shoulder or scapular bracing on posture and scapular muscle activity. OBJECTIVE To examine whether a scapular stabilization brace acutely alters posture and scapular muscle activity in healthy overhead athletes with forward-head, rounded-shoulder posture (FHRSP). DESIGN Randomized controlled clinical trial. SETTING Applied biomechanics laboratory. PATIENTS OR OTHER PARTICIPANTS Thirty-eight healthy overhead athletes with FHRSP. INTERVENTION(S) Participants were assigned randomly to 2 groups: compression shirt with no strap tension (S) and compression shirt with the straps fully tensioned (S + T). Posture was measured using lateral-view photography with retroreflective markers. Electromyography (EMG) of the upper trapezius (UT), middle trapezius (MT), lower trapezius (LT), and serratus anterior (SA) in the dominant upper extremity was measured during 4 exercises (scapular punches, Ws, Ys, Ts) and 2 glenohumeral motions (forward flexion, shoulder extension). Posture and exercise EMG measurements were taken with and without the brace applied. MAIN OUTCOME MEASURE(S) Head and shoulder angles were measured from lateral-view digital photographs. Normalized surface EMG was used to assess mean muscle activation of the UT, MT, LT, and SA. RESULTS Application of the brace decreased forward shoulder angle in the S + T condition. Brace application also caused a small increase in LT EMG during forward flexion and Ys and a small decrease in UT and MT EMG during shoulder extension. Brace application in the S + T group decreased UT EMG during Ws, whereas UT EMG increased during Ws in the S group. CONCLUSIONS Application of the scapular brace improved shoulder posture and scapular muscle activity, but EMG changes were highly variable. Use of a scapular brace might improve shoulder posture and muscle activity in overhead athletes with poor posture.

Neuromuscular Fatigue Alters Postural Control and Sagittal Plane Hip Biomechanics in Active Females With Anterior Cruciate Ligament Reconstruction

Background: Females with history of anterior cruciate ligament (ACL) injury and subsequent ligament reconstruction are at high risk for future ACL injury. Fatigue may influence the increased risk of future injury in females by altering lower extremity biomechanics and postural control. Hypothesis: Fatigue will promote lower extremity biomechanics and postural control deficits associated with ACL injury. Study Design: Descriptive laboratory study. Methods: Fourteen physically active females with ACL reconstruction (mean age, 19.64 ± 1.5 years; mean height, 163.52 ± 6.18 cm; mean mass, 62.6 ± 13.97 kg) volunteered for this study. Postural control and lower extremity biomechanics were assessed in the surgical limb during single-leg balance and jump-landing tasks before and after a fatigue protocol. Main outcome measures were 3-dimensional hip and knee joint angles at initial contact, peak angles, joint angular displacements and peak net joint moments, anterior tibial shear force, and vertical ground reaction force during the first 50% of the loading phase of the jump-landing task. During the single-leg stance task, the main outcome measure was center of pressure sway speed. Results: Initial contact hip flexion angle decreased (t = −2.82, P = 0.01; prefatigue, 40.98° ± 9.79°; postfatigue, 36.75° ± 8.61°) from pre- to postfatigue. Hip flexion displacement (t = 2.23, P = 0.04; prefatigue, 45.19° ± 14.1°; postfatigue, 47.48° ± 14.21°) and center of pressure sway speed (t = 3.95, P < 0.05; prefatigue, 5.18 ± 0.96 cm/s; postfatigue, 6.20 ± 1.72 cm/s) increased from pre- to postfatigue. There was a trending increase in hip flexion moment (t = 2.14, P = 0.05; prefatigue, 1.66 ± 0.68 Nm/kg/m; postfatigue, 1.91 ± 0.62 Nm/kg/m) from pre- to postfatigue. Conclusion: Fatigue may induce lower extremity biomechanics and postural control deficits that may be associated with ACL injury in physically active females with ACL reconstruction. Clinical Relevance: Rehabilitation and maintenance programs should incorporate activities that aim to improve muscular endurance and improve the neuromuscular system’s tolerance to fatiguing exercise in efforts to maintain stability and safe landing technique during subsequent physical activity.

Effect of ice hockey helmet fit on cervical spine motion during an emergency log roll procedure.

Objective:To investigate cervical spine motion during a log roll technique in ice hockey players under different helmet fit conditions. Design:Prospective counterbalanced design. Setting:University research laboratory. Participants:Eighteen club ice hockey players were recruited to participate in this study. Assessment of Risk Factors:A standard emergency log roll was performed 3 times under each of 3 different helmet fit conditions: properly fit, improperly (competition) fit, and helmet-removed. Main Outcome Measurements:Frontal, sagittal, and transverse plane cervical spine motion were used as outcome measures. Results:Significantly less sagittal and transverse plane motion occurred during the helmet-removed condition. No differences in frontal plane motion among the 3 conditions were observed. Conclusions:Presence of helmet (whether properly fit or not) resulted in increased of sagittal and transverse plane movement. This suggests that when an ice hockey helmet is stabilized, the head within it is not. We recommend the helmet and face shield be removed before performing an emergency prone log roll.

Focusing the direction of our profession: athletic trainers in America's health care system.

For some time now, I have been concerned that as a profession, we have lost focus regarding exactly what it is that athletic trainers (ATs) do. Athletic trainers have played a unique and important role in our health care system. Moreover, ATs value the contributions sport and exercise make to the health and development of young athletes and recognize the importance of a physically active lifestyle for all. From the beginning, ATs have sought to prevent sportand exercise-related injury. We treat patients engaged in exercise and strenuous work related to competitive sports, recreation, and work. In this issue of the Journal of Athletic Training, the need for ATs in high school, middle school, and youth programs becomes clear. Steinberg et al report on the high incidence of injury in young dancers, whereas Bowman and Bradney highlight the need to have welltrained health care professionals on-site to examine and treat injured and ill athletes. We know that every professional sport team, college, and university employs 1 or more ATs. But it may come as a surprise to realize that of the more than 41 000 US public and private high schools, about 42% (17 000) of these ‘‘have access’’ to an AT, according to the National Athletic Trainers’ Association. That means that more than 24 000 high schools currently have no AT at all. Even if only 1 AT is hired for each of these high schools, the potential market for jobs is huge, and this doesn’t even begin to take into account the potential job possibilities at middle schools. Despite this wealth of job opportunities, the push by our association has been to broaden the scope of practice for ATs to find work as physician extenders, in industry, or in clinics with a variety of patient populations who are different from the physically active population. This focus has created conflict between ATs and physical therapists and, in some cases, occupational therapists who are competing for the same patients in the health care marketplace. Athletic trainers have been trying, with limited success, to make a case to both employers and third-party payers that we are every bit as prepared as physical therapists, occupational therapists, and other health care providers to work with diverse patient populations. Athletic trainers are extremely well prepared to deal with physically active patients who have sustained injuries related to sport activity. In fact, we have better academic preparation and clinical training than ANY other group of health care professionals to work with this population. I firmly believe that many of the challenging issues negatively affecting our profession could be eliminated by refocusing on what we do well. We are health care providers. However, we should focus on providing health care to competitive and recreationally active patients at all levels; this is our niche within the health care system, and we are very good at it. No other professional is prepared to direct prevention efforts, provide on-site emergency and nonemergency care, direct appropriate follow-up, and ensure sufficient rehabilitation and recovery for return to safe participation in sports. In doing so, we provide a much needed service to a very specific patient population in a health care setting that, frankly, very few other health care professions are interested in serving. How can we accomplish this?