The purpose ofthis study was to determine the fatigue-induced compensations of the shouldercomplex in adolescent volleyball players after a jump-float serve fatiguingprotocol. The results indicate that the adolescent volleyball athlete experiencedno change in the MPF of the upper trapezius, middle trapezius, lower trapezius,and infraspinatus muscle; and an increased MPF of the posterior deltoid. On theother hand, the lower trapezius experienced significant fatigue after thejump-float serve fatiguing protocol. Therefore, the researcher must reject thehypothesis and accept the null hypothesis, as the infraspinatus did not experiencesignificant fatigue. This discussion will examine the causes for our results,make connections between adolescent volleyball players and SIS, recognizelimitations, consider the clinical implications and identify ideas for furtherresearch. Shoulder Muscle Fatigue and Shoulder Impingement Syndrome LiteratureSupportThe investigatorof this study conducted a systematic review and identified, four articles thatreported on the effects of infraspinatus muscle fatigue after a shoulderfatiguing protocol, using electromyography. Contrary to our results, three ofthe four studies found that participants experienced significant fatigue of theinfraspinatus muscle and no change of the lower trapezius muscle.
15,19,20Onthe other hand, Joshi et al. found a decrease in the MPF of the lowertrapezius, similar to the findings of our study.21 Shea et al., who observedfatigue-induced compensations of the shoulder complex in National Collegiate AthleticAssociation Division 1 female volleyball players, also reported a reduction inthe MPF of the lower trapezius muscle after a jump-float serve fatiguingprotocol.The significantfatigue in the lower trapezius is true for several reasons. It is important tonote that the lower trapezius functions to depress and stabilize the scapulathroughout shoulder elevation in order for the humerus to clear under thesubacromial arch during the jump-float serve.15 Therefore, prolonged andrepetitive contractions may have greater contributions to the fatigue of thelower trapezius muscle in our subjects. 21 In fact, Joshi et al.
believedactivities that require shoulder external rotation at 90° of GHabduction facilitates greater activation of the lower trapezius than the infraspinatus.21 Fatigue-InducedCompensationsDespite thesignificant fatigue seen in the lower trapezius, the infraspinatus didexperience a decline in the EMG amplitude during serving interval 11, while theEMG amplitude of the lower trapezius experienced a rise during serving interval12. This fatigue-induced compensation between the lower trapezius andinfraspinatus is opposite of the trend that Joshi and colleagues reported: significantfatigue in the lower trapezius correlated with a significant increase in muscleactivity of the infraspinatus. Perhaps, the inclination of the EMG amplitude ofthe lower trapezius and upper trapezius occurred because our subjectanticipated the end of the fatiguing protocol. This anticipation motivated thesubject to increase her serving intensity in order to finish the protocol strong.Orperchance, the altered activity of the infraspinatus muscle affected thelength-tension relationship for the lower trapezius. The alteration in muscle activationcan influence positional changes at the GH and ST joints, thus stretching amuscle to its ideal length allowing for maximal muscular contraction (https://study.
com/academy/lesson/length-tension-relationship-in-skeletal-muscle.html).Such decrease in infraspinatus muscle activity may produce an unstableGH joint, which can affect the center of rotation of the ST joint, and alterthe length-tension relations for the surrounding muscles.21,25 Therefore,the increase in the lower trapezius muscle activation could be a compensatorymechanism, where the fatigue of the infraspinatus lead to altered kinematicsthat lengthened the lower trapezius to the ideal position to increase its forceproduction in order to continue to generate the serving motion. 21 The connectionbetween muscle fatigue and altered kinematics was also noted in theinvestigator’s systematic review. Furthermore, an increase in scapular upwardrotation was reported in all four studies after the fatiguing protocol. Thismotion is contrary to GH and ST kinematics that is documented in individualswith SIS.
In fact, normal shoulder motion during elevation involves scapularupward rotation. 15,19-21However, results from a study by Karduna et al. found that with an increase inscapular upward rotation there was a reduction in the subacromial clearance incadavers.26 Perhaps, an increase inscapular upward rotation seen in the fatiguing protocol suggests that there isa compensatory mechanism where ST motion is altered as a results of rotatorcuff muscle fatigue.15,27 As such, the compensatoryresponse may promote scapular upward rotation as a way to clear humerus underthe subacromial space and reduce the possibility of SIS.
15,27 Regardless, shoulder musclefatigue can alter shoulder kinematics, making one susceptible to SIS. As such,knowledge concerning muscle fatigue in adolescents is especially important dueto kinematic changes associated with SIS, but also given the incompletedevelopment of their musculoskeletal system and earlier sport specialization.1Volleyball Adolescent Athlete and Muscle FatigueIt is also importantto point out that the subject of the current study experienced significantreductions in muscle activation 20 minutes sooner than the collegiate athletesin the study by Shea et al. This difference highlights that there are qualitiesin our subject that increase her risk of muscular fatigue and developing SIS. Thus far,the literature supports the role that muscle fatigue plays on the developmentof SIS.
Yet, the connection regarding why an adolescent volleyball player who isat an increased risk of muscle fatigue may also have increased susceptibilityto SIS, has not been made. Nonetheless, lack of skeletal maturity andsport specialization is often emphasized as the primary means for injuries inadolescents; these factors also seem to best fit our subject’s profile.22,25,28,29SkeletalMaturity and Muscle FatigueFull skeletalmaturity occurs by 15 years old in females and 18 years old in male (https://pedsforparents.wordpress.com/tag/skeletal-maturity/).25,28The risk of an injury is increased in the adolescent athlete due to their bonegrowth and development. Furthermore, long bone growth advances rapidly, leavinginadequate time for compensatory elongation and flexibility of the accompanyingmuscle tendon units. 22 Loss of flexibility and rapidgrowth is likely to contribute to muscle-tendon imbalances and such imbalancesmay result in tendon injuries.
22 The growing bone anddeveloping musculoskeletal system of adolescent athletes cannot handle therepetitive stress as the mature adult skeleton. 22,25,29Thus, when this repetitive stress is applied to a muscle, tendon, or bone,overuse injuries occur. Overuse injuriesin adolescent athletes has become an increasing concern among pediatric health.
22 Nearly 50% of injuriespresenting to pediatric sports medicine practice are related to overuse. 22,25,29In fact, overuse injuries account for 46% to 50% of all athletic injuries; inhigh school athletes alone, overuse injuries represented 7.7% of all injuries. 28 Overuse injuries result inmicro-traumatic damage, especially when the athlete has not allotted adequatetime for the tissue to heal or repair. Additionally, overuse injuries canoriginate from muscle fatigue, and develop into irritable syndromes of themuscle, tendon, and bone.30 As such, SIS in overheadathletes is the most common overuse injury of the shoulder in overhead athletesdue to the repetitive stress placed upon the shoulder musculature (Overuse andImpingement Syndromes of the shoulder in the athlete by Cowderoy GA et al,Lisle DA, O’Connell PT).
Reasons for overuse injuries can be split intointrinsic and extrinsic factors. Intrinsic riskfactors include anatomy, the growth and development of the adolescent,nutrition, pre-existing conditions, height, sex, age, menstrual cycle, andpsychological matters. 18,33The athlete’s psychological disposition is an important factor to consider inregards to overuse injuries. There is often a disconnection between anathlete’s mind and body. The adolescent athlete may be unable to cognitivelyconnect fatigue or poor performance and mechanics as a potential sign of anoveruse injury.25 Athletes may not considerthemselves fatigue, although the EMG activity of the muscles suggest otherwise.This impaired perception of true muscle fatigue correlates to the notion of “no pain, no gain” that most athletes embrace.It is likely that volleyballathletes are practicing through shoulder musculature fatigue, which increasestheir likelihood for altered shoulder kinematics leading to the development of SIS.
Running several drills, during practice, to perfect the jump-float serve andother overhead skilled activities is inevitable. However, coaches can implementstrategies to allot adequate resting time to unload stress to a single jointand stress to the same muscle group.2 For instance, since thesubject of the current study experienced fatigue by the 40th serve,perhaps 40 or fewer repetitions of serving or other overhead tasks without restor in a single drill, is the limit for this age group. After the 40-serve cap,other drills could be performed emphasizing use of the lower extremity or even theupper extremity below 60 degrees of elevation, such as passing. By implementingthis strategy, it allows for additional rest time between bouts of the overheadactivity. Just as intrinsicrisk factors play a role in overuse injuries, extrinsic risk factors have largecontributions. Extrinsic risk factors are often modifiable, thus physical therapistsplay a crucial role in preventing overuse injuries by educating parents andyoung athletes regarding the risk of adolescent sport injuries.
Identifyingadolescents at risk of overuse injuries is the first step to injury prevention,injury reduction and early recognition. 25 Several extrinsic factorsthat are often identified for injury prevention include training error,equipment, poor technique, environment, conditioning, and early specialization. 18,33 SportSpecialization and Muscle FatigueSportspecialization occurs when an athlete focuses on only 1 sport and usuallyyear-round, as select or travel leagues start as young as 7 years old.
28 Although, only 3.3 to 11.3%of high school athletes compete at the NCAA level, and only 1% receives anathletic scholarship, parents and their young athletes decide to specialize forthe chance at being the 1%. 28 Sport specialization isbecoming increasingly common in youth sports. In fact, the athlete of thecurrent study specialized in volleyball at 13 years old. Consequently, thisincreased emphasis of sports specialization has led to an increase in overuseinjuries such as SIS, overtraining, and burnout since the same muscle groupsare performing the same movement patterns repeatedly. 29,28 Participating in adolescentssports has several benefits, including developing lifelong physical activityskills, socializing with peers, building teamwork and leadership skills, improvingself-esteem, and having fun.
28 Nonetheless, adolescentathletes who participate in only 1 sport are at higher risk for overuse injuriesthan those in multiple sports with different emphases.22 It is also theorized thatathletes who participate in a variety of sports have fewer injuries and playsports longer, and a higher likelihood of athletic success than those whospecialize before puberty. 35 Infact, early diversification and later specialization is recommended as itprovides a greater opportunity of lifetime sports involvement, physicalfitness, and possibly elite participation. 22,28AdolescentVolleyball Players and Shoulder Impingement SyndromeUnfortunately, theexact amount of training needed to succeed in volleyball, is unknown, as is thethreshold to avoid injuries and burnout. However, it is documented that fatigueleads to SIS in overhead athletes due to the altered kinematics associated withmuscle fatigue. Since our subject specialized in volleyball before full maturityof her musculoskeletal system, it is likely that the repetitive stress placedon the same shoulder muscle groups was too much for her undevelopedmusculoskeletal system to handle. This frequent stress from repetitive shouldermotion increases her risk of muscular fatigue.
And as shown in research, musclefatigue can lead to altered shoulder kinematics and ultimately the developmentof SIS. Thus, educating our athletes and their parents on injury prevention maydecrease a volleyball player’s risk of SIS.35Injury PreventionIt is essentialfor physical therapists and other members of the sport medicine team, to understandand perform biomechanical and functional assessments on our athletes.
23 Understanding what the sportentails and applying the aforementioned skills prior to a sporting season mayincrease an athlete’s longevity of play by identifying risk factors for injury.This can be done by assessing an athlete’s preparedness to meet physicaldemands of their sport.23 Pearce believes that apre-participation physical examination should be performed annually, by aphysical therapist or other certified personnel, to accommodate for thechanging growth in adolescents, and 6 to 8 weeks before training or competing,to allow for rehabilitation of previous injuries. 23 The physical examination shouldinclude range of motion and functional strength of the upper and lowerextremities. The scapular stabilizing muscles are often neglected as a role inshoulder function.
However, the scapular stabilizing muscles play several rolesin promoting optimal shoulder stability, when elevated above 60 degrees, to produceefficient movement.4 Therefore, adequate strengthof the muscles surrounding the GH and ST joint are especially important inadolescent volleyball players. However, if thematter at hand (adolescent volleyball players and their risk of SIS) truly stemsfrom skeletal immaturity and sport specialization, then it is also important toeducate and guide our athletes and their parents accordingly. Thus, sportspecialization has increased as athletes and parents seek to be the few whoobtain an athletic scholarship or make it to elite levels. However, delayingsport specialization until late adolescence, 15 or 16 years old, may minimizethe risks for overuse injuries and lead to a higher likelihood of athleticsuccess due to skeletal maturity.28 Nevertheless, a well-roundedmultisport athlete, regardless of age, has the highest potential to achieve thegoal of lifelong fitness and enjoyment with physical activity.25 Yet, for thoseathletes and parents who continue to seek sport specialization, The AmericanAcademy of Pediatrics Council on Sports Medicine and Fitness have severalsuggestions for the athlete, parent, and coach. 22,25,28Some of which include: (1) preseason and in-season preventive training programsfocusing on neuromuscular control, balance, coordination, flexibility, andstrengthening, (2) at least 1 to 2 days off per week from competitivepractices, competitions, and sport-specific training, (3) participate on only 1team of the same sport per season, (4) progression of training intensity, load,time, and distance should only increase by 10% each week to allow for adequateadaptation and to avoid overload, (5) having at least a total of 3 months offthroughout the year from the sport of interest, but still remain active inother activities to meet physical activity guidelines, and (6) after injury, overheadathletes should pursue a gradual return-to-sport program over several weeksbefore resuming full overhead activities.
22,25,28Not only can we encouragethat adolescent athletes follow set guidelines, we can also suggest that theseathletes implement different theories with the focus of countering thedetrimental effects of sport specialization. 28 For example, long-termathlete development (LTAD) programs, which started in the 1990s in the UnitedStates, Canada, and other industrialized countries implemented frameworks toavoid the effects of early sport specialization and promote physical literacyor mastering of fundamental movement skills and fundamental sports skills.28 LTAD is made up of 5 phasesall of which entail a goal as well as age ranges in order to prevent burnout(Table 2). LimitationsThe investigatorrecognizes some limitations within the study. Our participant sample was madeup of only one subject. The sample is not a sufficient representation for theadolescent volleyball population, which is a threat to external validity (2016Spring Reliability and Validity lecture by Dr. Cheryl Hickey). Only one subjectwas observed because this is a pilot study as part of a bigger project lookingat muscle fatigue, kinematics, and motion analysis in adolescent volleyballplayers.
Lastly, the subject included did not have a previous history ofshoulder pathology; this information should be kept in mind when interpreting andcomparing the results of similar studies.Changes in methodology,regarding the shoulder and body positioning during the fatiguing protocoldiffers between the studies. These changes may contribute to the differences inthe results. For example, Chopp-Hurley et al. positioned their participantsprone with their arm fully extended and abducted to 60° in the coronal plane. 20Joshi et al. positioned their participants in prone with the shoulderpositioned in 90° of abduction.
21 The participants in the studyby Ebaugh et al. (2006) were standing and achieved up to 160 degrees ofshoulder elevation.19Ebaugh et al. (2005) instructed their subjects to lie on their non-tested sidewith their shoulder abducted to 10° to 20° of abduction in the frontalplane.15 Also, theinvestigator of the current study as well as Shea et al. placed the surfaceelectrodes based upon guidelines from SENIAM (http://seniam.
org). However, itis unclear if similar placement was performed in the other studies, which canalso lead to discrepancies among the results of the studies. One of thedisadvantages of using surface electromyography is the lack of selectivity or crosstalkof the surrounding muscles. As such, the electromyography readings may containcontributions from proximal muscles over which the electrode was placed such asthe rhomboids and latissimus, which can lead to mistaken conclusion. Also, thisstudy only observed fatigue of 5 muscles. Thus, the conclusions drawn can onlybe relevant between those muscles; but perhaps other muscles that were notobserved such as the serratus anterior was activated to a greater extent, whichmay explain other compensatory mechanism. Observing changesin MPF between the serving intervals is just one way to measure muscle fatigue.Assessing the individual’s heart rate is another indicator of potential musclefatigue or overtraining.
30 Unfortunately, heart rate wasnot assessed throughout the fatiguing protocol. Monitoring an individual’sheart rate allows the investigator to ensure that an individual’s physiologicalstatus and training tolerance is appropriate to continue the fatiguing protocol(https://certification.acsm.org/blog/2015/july/using-heart-rate-monitoring-for-personal-training).
30 Nevertheless, the investigatorsof the study did use other methods to avoid placing the athlete at risk ofinjury. Moreover, volleyball athletes with prior shoulder surgery or shoulderinjury over the past two weeks were deemed ineligible. Termination of thefatigue protocol would occur if the subject reported a ?18/20 on the Borg Scale ofperceived exertion and ? 8/10 on the fatigue scale. Lastly, observations such asfacial grimaces and gradual reductions in shoulder motion during the serving protocolwere also a measure for termination of the fatigue protocol to promote thesubject’s safety.ConclusionOverall, twoconclusions were generated: (1) shoulder muscle fatigue leads to alterations inshoulder kinematics that are associated with SIS and (2) since this adolescentvolleyball player is susceptible to fatigue, due to sport specialization beforereaching skeletal maturity, she too is at risk for developing SIS. Therefore,it is likely that other adolescent volleyball players who share similar riskfactors may also be at risk for developing SIS.
Fatigue-inducedprotocols, simulating overhead activities above shoulder height, requires muchdemand from the rotator cuff and scapula stabilizing muscles, and givesresearchers an opportunity to identify risk factors for SIS in a controlled andsafe setting. Such information is critical to prevent shoulder injuries andincrease an adolescent volleyball athlete’s longevity of play. Conciseknowledge regarding fatigue and SIS in adolescent volleyball players, givesinsight to physical therapists and other members of the sport medicine team toimproved examination tools and evidence-based practice tailored for adolescentvolleyball players.
Thus, future research is warranted, using consistentmethodology, to examine shoulder muscle fatigue and shoulder kinematicssimultanesouly, during a fatiguing protocol in adolescent volleyball players.