Question

Read the article, more specifically the abstract, introduction, discussion and conlcusion and summarize those specific sections in a paragraph or two.

SYSTEMATIC REVIEW THE INFLUENCE OF EXTRINSIC FACTORS ON KNEE BIOMECHANICS DURING CYCLING: A SYSTEMATIC REVIEW OF THE LITERATURE Therese E. Johnston, PT, PhD, MBA Tiara A. Baskins, DPT Rachael V. Koppel, DPT Samuel A. Oliver, DPT" Donald J. Stieber, DPT Lisa T. Hoglund, PT, PhD, oCS Background: The knee is susceptible to injury during cycling due to the repetitive nature of the activity while gen- erating torque on the pedal. Knee pain is the most common overuse related injury reported by cyclists, and intrinsic and extrinsic factors can contribute to the development of knee pain. Purpose: Due to the potential for various knee injuries, this purpose of this systematic review of the literature was to determine the association between biomechanical factors and knee injury risk in cyclists. Study Design: Systematic review of the literature Methods: Literature scarches were performed using CINAHL, Ovid, PubMed, Scopus and SPORTDiscus. Quality of studies was assessed using the Downs and Black Scale for non-randomized trials. Results: Fourteen papers were identified that met inclusion and exclusion criteria. Only four studies included cyclists with knee pain. Studies were small with sample sizes ranging from 9-24 participants, and were of low to moderate quality. Biomechanical factors that may impact knee pain include cadence, power output, crank length, saddle fore/ aft position, saddle height, and foot position. Changing these ctors may lead to differing effects for cyclists who experience knee pain based on specific anatomical location Conclusion: Changes in cycling parameters or positioning on the bicycle can impact movement, forces, and muscie activity around the knee. While studies show differences across some of the extrinsic factors included in this review there is a lack of direct association between parameters/positioning on the cycle and knee injury risk due to the limited studies examining cyclists with and without pain or injury. The results of this review can provide guidance to professionals treating cyclists with knee pain, but more research is needed. Level of Evidence: 3a Key Words: Biomechanics, cycling, knee injury, knee pain, overuse CORRESPONDING AUTHOR Therese E. Johnston, PT, PhD, MBA Department of Physical Therapy, Jefferson College of Health Professions 901 Walnut Street, Room 515, Philadelphia, PA 19107 Department of Physical Therapy, Jefferson College of Health Professions, Philadelphia, PA, USA E-mail: therese The Irternational Journal of Sports Physical TherapyI Volume 12, Number 7 December 2017Page 1023 DOI: 1016603/jspt20171023

INTRODUCTION

With the increase in recreational and competitive cycling, cyclists are experiencing more overuse inju- ries related to repetitive loading.Both intrinsic and extrinsic factors contribute to injury. Intrinsic fac- tors are inherent to the cyclist and include fitness level as well as anatomical alignment of the lower extremities. Extrinsic factors are generally asso- ciated with factors external to the cyclist such as equipment, riding technique, and training.

The knee is the most common joint impacted by cycling overuse injuries in recreational and pro- fessional cyclists.Knee pain is reported to affect 40-60% of recreational cyclists and 36-62% of profes- sional cyclists. Anterior knee pain is the most common, which is likely due to patellofemoral pain, patellar tendinopathy, or quadriceps tendinopa- thy. Factors that may cause anterior knee pain include increased pressure due to hill climbing, heavy workloads, increased training, altered patel- lar tracking, or by a combination of factors. Many risk factors can contribute to the problem such as altered patellar position, decreased flexibility, increased quadriceps (Q) angle, muscle imbalances, and various limb torsional and foot deformities. In a review article, Johnston reported that cycling cadence and workload impact moments around the knee, which may contribute to knee injury at higher effort levels. Increasing knee flexion angle can increase forces impacting the knee8 while co- contraction of the knee flexors and extensors can decrease them.9 Thus the interaction of these vari- ables as well as power output and cycling duration may be important in understanding cyclists who are at greater risk of injury due to loading.

Several knee structures are potentially at risk for over- use injury with cycling due to intrinsic and extrinsic factors. Patellofemoral pain (PFP) is one of the most common causes of knee pain in cyclists, resulting in anterior knee pain.5 Female gender is a risk fac- tor for PFP,10 and PFP is more common in female cyclists. An additional risk factor is reduced quadri- ceps strength,10 which may cause the greatest preva- lence of PFP during preseason training in cyclists.4 Additional associated factors with PFP in cyclists include excessive varus knee moments during the power stroke, excessive valgus knee alignment, repetitive loading of the patella, weak gluteal mus- cles, increased Q angles, excessive patellar lat- eral tilt,5 and excessive foot pronation. Patellar and quadriceps tendinopathies are additional causes of anterior knee pain in cyclists, 5 which are caused by chronic repetitive overload of tendons during quadri- ceps contractions. Iliotibial band (ITB) syndrome is the most common cause of lateral knee pain in cyclists.2 Proposed mechanisms for ITB syndrome are compression of fat beneath the ITB at the lateral femoral epicondyle or friction of the ITB as it moves across the lateral femoral epicondyle during repeti- tive knee flexion and extension.2,11,16 When the knee reaches 20-30° of flexion, the ITB passes over the lateral femoral epicondyle,17,18 creating an impinge- ment zone for fat and an adventitial bursa.2,5,11 ITB syndrome is likely caused by increased tibial inter- nal rotation, ITB tightness, inward pointing of toes on the pedals, increased hip adduction, a bicycle saddle position that is too high, and rapid increase in mileage.1,2,5,16,19 Medial knee injuries seen in cyclists include medial collateral ligament bursitis, plica syn- drome, pes anserine syndrome and medial meniscus tear.2 Plica syndrome is characterized by pain, snap- ping or clicking sensations as inflamed remnants of synovial tissue impinge against the anterior medial femoral condyle as the knee flexes and extends.2,20 Medial meniscus tear is least likely to occur in cyclists, but can be symptomatic when rotating the leg to release the shoe from the pedal.2 The poste- rior knee is the least commonly injured and may be attributed to biceps femoris tendinopathy presenting posterolaterally.2 The etiology of biceps femoris ten- dinopathy is chronic overload of the hamstring mus- cles and tendons, and may be due to tight hamstrings or an excessively high saddle.21

Due to the potential for various knee injuries, this purpose of this systematic review of the literature was to determine the association between biomechanical factors and knee injury risk in cyclists. To accom- plish this goal, biomechanical studies that examined extrinsic factors including kinematics, kinetics, and/ or muscle activity under various cycling conditions and cycle component settings were included.

DISCUSSION

Cycling parameters (i.e., cadence and power out- put) and bicycle fit settings have differing effects on kinematics, kinetics, and muscle activity around the knee. Few studies compared cyclists with and with- out knee pain, so injury risk can only be surmised based on the results of biomechanical studies that examine cyclists without injury or pain. There is also a lack of longitudinal studies to assess the effects of altering parameters on knee injury and pain. Thus, causation cannot be determined.

Studies examining cycling kinetics indicate that vari- ous stresses are imparted on the knee based on a vari- ety of kinetic variables. Vertical and anterior pedal reaction forces increase at higher cadences,30 and vertical and medial pedal reaction forces increase at higher power outputs.30 Tibiofemoral peak anterior shear forces were found to be increased at higher saddle heights,34 and ankle inversion increased peak vertical forces.12 These findings are in partial agree- ment with an earlier study by Ericson and Nisell,37 which reported that higher saddle heights signifi- cantly increased tibiofemoral anterior shear forces, but decreased tibiofemoral compressive forces. The findings of the studies in this systematic review and earlier studies have implications for loading of the knee joint during cycling and suggest that lower cadences, lower workloads, a higher saddle height, and foot eversion might be preferred for cyclists with knee pain due to tibiofemoral compres- sive joint loading, such as with medial tibiofemoral OA. In contrast, cyclists with anterior cruciate liga- ment injury or reconstruction may benefit from a

ower saddle height and lower cadences.30,34,37 How- ever, force effectiveness, a measure of force output in relation to angle of force application, may be decreased with these settings,29 and thus the effects of combining these conditions is unknown. The effect of crank length due to loading is more diffi- cult to interpret as a shorter crank length at a higher cadence increases power output,25 yet increased crank lengths may shift more of the power produc- tion from the knee extensors to the hip extensors.27 When comparing the moments around the knee to other activities such as walking, jogging, and stair climbing, the extension and flexion moments are generally smaller when cycling at 120 Watts. At 240 Watts, the loads were similar to the other activities.38 Knee injuries are the most commonly reported inju- ries in cyclists, thus it may be the combined effects of workload, cadence, and positioning on the cycle that contribute to injury.

Shear forces are another concern in cyclists, par- ticularly possible injury to the anterior cruciate ligament (ACL) or after an ACL reconstruction. Tib- iofemoral anterior shear forces may decrease with a more forward28 or lower saddle position,34 decreas- ing potential strain on the ACL. However, studies reported low in vivo ACL strain39 and low anterior tibiofemoral shear force37 during cycling. Fleming et al.39 reported that strain on the ACL during cycling was approximately 1.7%, and did not change sig- nificantly with alteration of cadence or power level. Strain on the ACL during cycling was low compared to 3.6% while squatting and 2.8% while extending the knee from flexion.39 Strong contraction of the hamstrings during the second half of the power phase may minimize ACL strain.40 Posterior pull of the hamstrings on the tibia when the crank angle is 180° from top dead center may limit ACL strain as the knee approaches its least flexed position of 37°,41 an angle which is within the range of great- est ACL strain during activities, 0° - 50° flexion.42 While shear forces on the ACL during cycling appear to be low, more research is needed to examine shear forces on the posterior cruciate ligament and patella during cycling. Thus, cyclists with anterior cruciate ligament injury or reconstruction may benefit from a lower saddle height or more forward saddle posi- tion.28,34 as well as a lower cadence.30

Medial and lateral regions of the knee are also sus- ceptible to injury. Coronal plane forces are affected by foot position, with eversion lowering peak varus and internal axial moments and increasing vastus medialis activation compared to inversion.12 For people with medial knee OA, rotating the shank to increase toe-in angle reduced peak knee adduc- tion angles, with no impact on peak knee abduction moments.36 Gardner et al.36 hypothesized that an alignment change with increased toe-in foot posi- tion would decrease the frontal plane moment arm of the pedal reaction force, which would decrease knee abduction moments. As competitive cyclists and people with knee OA differ in knee alignment, findings may be specific to these populations. One study examined the impact of saddle height on ITB syndrome and reported that a lower saddle height that increased minimum knee flexion angle to greater than 30° kept the ITB out of the impinge- ment zone.31 For cyclists at risk for ITB pain, a lower seat height may also be desirable by reducing com- pensatory lateral pelvic motion31 that can increase stress to the ITB. Overall, more research is needed to better understand the effects of cycling on the medial and lateral regions of the knee.

Few studies have examined PFP in cyclists specifi- cally, which is surprising due to the prevalence of anterior knee pain in cyclists.2 One study reported differences in muscle activation between cyclists with and without PFP.35 Although no differences were found between groups for vastus medialis onset times, the slower contraction offset time of vastus lateralis relative to vastus medialis in the PFP cyclist group may be associated with lateral patellar mal- tracking.35 These findings are consistent with a sys- tematic review that did not find a difference in vastus medialis and vastus lateralis contraction onset in per- sons with PFP, but reported significant variability in muscle activation ratio.43 Dieter et al.35 also reported earlier contraction onset and later offset time of the biceps femoris relative to the semitendinosus in the PFP group compared to controls.35 These changes may result in increased tibial external rotation, with a resultant increase in the dynamic Q angle and potentially increased lateral patellofemoral joint stress.44,45 As the hamstrings are active longer than the quadriceps during cycling,21 altered hamstring

activation may be more critical to development of PFP in cyclists compared to vasti activation. How- ever, it is unknown if altered muscle activation is compensatory to or a cause of PFP. Altered coronal plane knee position may be associated with PFP as reduced knee adduction angles, that is, a more val- gus position, are seen in cyclists with anterior knee pain or patellar tendonitis.24 Studies in this system- atic review that examined the impact of saddle posi- tion on patellofemoral compressive forces did not find significant differences.28,33 In contrast, an earlier study by Ericson and Nisell8 reported that a lower saddle increased patellofemoral joint compressive forces. Although increased knee flexion from a lower saddle position would increase patellofemoral joint reaction force,46 patellofemoral joint cartilage stress does not increase linearly with increasing knee flexion from 0° to 90°.47 Patellofemoral joint stress increases to a lesser degree than patellofemoral joint reaction force with increasing knee flexion due to increased patellofemoral joint contact surface area.47 Tamborindeguy and Bini33 found the highest patel- lofemoral compressive force occurred with the knee at approximately 75°-80°. Thus, patellofemoral joint stress may be minimized during cycling by greater patellofemoral joint contact area at knee joint posi- tions which have high patellofemoral joint reaction forces.47 PFP in cyclists may not be related to high joint stress, but rather secondary to frequent patello- femoral joint loading from repetitive knee extension. This repetitive loading could cause supraphysiologic loading of osseous and non-osseous structures poten- tially causing loss of tissue homeostasis and PFP.48,49 More research is needed to understand patellofemo- ral compressive and shear forces and how they are associated with risk of injury.

In the articles in this systemic review, no issues spe- cific to the posterior knee were discussed. Elmer et al.26 reported that knee flexion power increased relative to extension power as overall power out- put increased,26 which may have implications for biceps femoris tendinopathy.2 Interestingly, Dieter et al.35 found that biceps femoris muscle activation occurred prior to semitendinosus onset in cyclists with PFP, unlike those without this anterior pain condition. More research is needed on posterior knee pain in cyclists.

There are several limitations of this systematic review. Studies differed considerably in methodol- ogy, making qualitative or quantitative compari- sons challenging. It is also difficult to make strong recommendations as far as the amount of change needed to decrease injury risk as studies vary in the magnitude of changes in cycling parameters and bicycle settings. Bini et al.34 reported that even a 5% difference in saddle height can affect knee joint kinematics by 35% and joint moments by 16%;34 yet it is unknown how these differences then trans- late into injury risk. There is also the lack of direct association between parameters/positioning on the cycle and injury due to limited studies examining cyclists with and without pain or injury and a lack of longitudinal studies. More research is needed to establish clear links and recommendations by manipulating parameters based on the available lit- erature and knowledge of biomechanics impacting specific areas of the knee. Longer term effects on pain, performance, and participation should then be assessed. Another limitation is the inclusion of 2D measurements in some studies. 2D data capture can be misleading as movement outside of the sag- ittal plane impacts how each joint is visualized on a 2D image. In addition, 3D kinetic measurements are needed to fully understand the effects on the knee in all three planes.

CONCLUSIONS

The results of this systematic review indicate that changes in cycling parameters or positioning on the bicycle can impact movement, forces, and muscle activity around the knee. While studies showed dif- ferences across some of the extrinsic factors, there is a lack of direct association between parameters/ positioning on the cycle and knee injury. Despite the lack of this clear association, the results of this systematic review can provide guidance to profes- sionals treating cyclists with knee pain. The liter- ature provides important information about how biomechanical factors and positioning on the bicy- cle can increase or decrease stress in specific areas of the knee joint. Further research is needed with larger samples of cyclists with including those with- out knee pain to better understand direct relation- ships between these variables and knee pain during cycling.

Answer 1

Ans - The above article is based on study of knee injury due to long term cycling. The repeated events of cycling to produce torque on paddle of cycle causes knee pain.Knee being the most common joint to be impacted by the cycling, is result of knee pain in 40-60% in recreational cyclist and 36-62% in professional cyclist. Study reported that cycling cadence and workload impact moments around the knee contribute to knee injury at higher effort levels. various knee structures are at high risk for over- use injury with cycling such as Patellofemoral pain (PFP) is one of the most common reason of knee pain in cyclists and Female being at high risk of PFP. Another risk factor is reduced quadriceps strength which cause the greatest proliferation of PFP during preseason training. As competitive cyclists and people with knee OA differ in knee alignment, findings may be specific to these populations. forces applied due to cycling can also cause injury to anterior cruciate ligament. medial as well as lateral regions of are also at risk of injury. while a proper posture can minimise the risk of injury.
The study finally conclude that cycling parameters and positioning can impact movement and muscle activity around knee. however biochemical factors and proper postioning can reduce risk of injury.