ILIOTIBIAL BAND SYNDROME IN CYCLING: A COMBINED EXPERIMENTAL-SIMULATION APPROACH FOR ASSESSING THE EFFECT OF SADDLE SETBACK

Abstract

Background:

Despite abundant literature, the treatment of iliotibial band syndrome (ITBS) in cyclists remains complicated as it lacks evidence-based recommendations.

Purpose:

The aim of this study was to develop a musculoskeletal modelling approach that investigates three potential biomechanical determinants of ITBS (strain, strain rate and compression force) and to use this approach to investigate the effect of saddle setback.

Design:

Cross-sectional

Methods:

An existing 3D lower-body musculoskeletal model was adapted to cycling and to the computation of three putative pathomechanisms responsible for ITBS: ITB strain, ITB strain rate, and compression force between ITB and the lateral femoral epicondyle (LFE). Lower limb kinematics recorded from ten well-trained healthy cyclists served as input data of the model. Cyclists pedalled at a steady state (90rpm and 200W) on an ergometer, and three different saddle setback conditions were tested. The theoretical combined influence of hip and knee joint angles on ITBS was investigated and analysed through the lens of individual pedalling technique.

Results:

ITB-LFE compression force was the only parameter significantly affected by saddle setback and supports the hypothesis that compression force is likely to be a determinant factor in ITBS etiology. Furthermore, results showed that ITB-LFE compression force increases in individuals whose pedalling technique exacerbates hip extension-adduction and/or knee extension-internal rotation.

Conclusion:

This approach has the potential to be advantageously implemented as an additional tool to help diagnose/correct potentially harmful sport techniques and optimize equipment setup/design.

Level of evidence:

3b

INTRODUCTION

Bike fitting is a fast-growing industry with new companies steadily getting into the market. Bike fitting relates to bicycle ergonomics and can be defined as the process of setting-up specific bicycle parameters to best suit an individual and optimize the positioning of the cyclist. The ultimate goal is to improve a cyclist's performance while preserving his or her health since an incorrect bicycle configuration may predispose cyclists to overuse injuries.

Among the parameters that are adjusted, saddle setback position is known to influence variables related to performance and pedalling effectiveness, but its effect on overuse injuries such as cartilage/bone degradation and tendinopathies remains inconclusive.^1-4 Saddle setback refers to its fore-aft position, it is defined here as the horizontal distance between the center of the bottom bracket and the rear of the saddle.⁵ This implies that an increased saddle setback involves a more backward position of the saddle.⁵ Knee functional disorders are one of the most common lower extremity non-traumatic injuries reported by well-trained cyclists (about 50% of injured cyclists).⁶ Iliotibial band syndrome (ITBS), a commonly identified clinical condition characterized by focal lateral knee pain, comprises 15% of cycling overuse injuries.⁷

Numerous studies including several literature reviews have been conducted on ITBS etiology which is commonly acknowledged as “multifactorial”.^8-11 Since Renne's study it has been widely believed that friction resulting from the ITB sliding over the lateral femoral epicondyle (LFE) of the femur during repetitive knee flexion-extension is the major cause of pain.¹² On the contrary, anatomical observations indicate that the ITB is securely anchored onto the distal femur in a way that the ITB cannot create frictional forces by moving forward and backward over the LFE.¹³,¹⁴ Those authors argued in favour of a compression syndrome (pain would result from repetitive compression of the highly innervated fatty tissue beneath the distal aspect of the iliotibial band) rather than a friction syndrome.¹⁵ Others have suggested that ITB strain or strain rate may be a contributing factor.^16-18 Thus, the evidence of a single key parameter responsible for developing ITBS remains inconclusive and several biomechanical determinants may contribute.

In order to prevent the occurrence of ITBS in cycling, several recommendations have been made regarding body position and bicycle setup.^1,7,19,20 These recommendations are based on epidemiological studies rather than on the analysis of biomechanical determinants.¹⁹ Previous experimental research have tried to establish a link between ITBS and sport movements has mostly relied on kinematic analyses. Contradictory results were observed on the effect of hip adduction in running.^21,22 One single experimental study addressed the etiology of ITBS in cycling and the authors suggested that the repetition of knee flexion-extension movement close to 30 ° of knee flexion may be the primarily leading cause.²³ This last result was based on a retrospective evidence (the hypothetical impingement/friction zone around 30 ° knee flexion) and should, as such, be considered carefully.¹² In addition, given the biarticular nature of the ITB, a more thorough analysis of combined effects of all degrees of freedom of the hip and knee joints is necessary.²⁴ Furthermore, kinematic analysis alone fails to apprehend musculoskeletal solicitations. The analysis of musculoskeletal parameters (e.g. muscle length/velocity, muscle/joint forces) is more relevant but, because direct measurement during physical activity is impossible, musculoskeletal modelling is necessary.²⁵

The aim of this study was to develop a musculoskeletal modelling approach that investigates three potential biomechanical determinants of ITBS (strain, strain rate and compression force) and to use this approach to investigate the effect of saddle setback. Also, the theoretical combined influence of hip and knee joint angles on ITB-LFE compression force was investigated and analyzed through the lens of individual kinematic differences.

METHODS

Participants

Ten well-trained cyclists without history of knee pain or injury volunteered to participate in the study (age: 30.9 ± 8.6 years, height: 1.75 ± 0.05 m, weight: 65.2 ± 8.3 kg). Participants were informed of the procedures, methods, benefits, and possible risks involved in the study before their written consent was obtained. The study protocol was approved by the Ethics Committee of the University of Poitiers and met the requirements of the Declaration of Helsinki for research involving human participants.

Musculoskeletal modelling

A 3D musculoskeletal model of the lower body was adapted based on existing models.^26,27 Specifically, ITB force-length properties and attachment sites (origin on the iliac crest, intermediate insertion on the lateral femoral epicondyle (LFE) and termination on Gerdy's tubercle) reflected the most recent anatomical description of the ITB.^16,28 Analogous to the wrapping surface added by Miller's study, the LFE was modelled as an additional body whose surface was flush against the outer surface of the distal-lateral part of the femur.¹⁷ The two bodies connected with a weld joint (0 degree of freedom) so that the interaction force between ITB-LFE was entirely transmitted to the LFE-femur joint. ITB-LFE force could then be computed as the LFE-femur joint force. This astuteness allowed overcoming the absence (in Opensim software) of direct output of interaction force between a musculotendinous unit (e.g ITB) and an intermediate point (e.g LFE).

Kinematics data collection

A stationary cycle ergometer SRM “Indoor Trainer” (SRM, Schoberer, Germany) whose seat and handlebar position were fully adjustable was used. A 20-camera motion analysis system (Vicon Motion Analysis Inc., Oxford, UK) was used to acquire three-dimensional kinematics. The marker set (28 markers on the pelvis, lower limb and ergometer) followed Opensim and the International Society of Biomechanics recommendations (Figure 1).^29,30

Figure 1.

Illustration of the placement details for the marker set used on the pelvis, lower extremity, and foot/shoe.

Details regarding marker placements are provided in Appendix 1.

Experimental protocol

Three saddle positions were compared: a recommended setback condition that standardised values of saddle height and setback (distance between the rear of saddle and the axis of the chainset) based on individual anthropometric measurements, a backward (10% more backward) and a forward (10% more forward) setback conditions.³¹ The actual sitting position (location of the center of pressure on the saddle) was tracked during pedalling using a force sensor integrated within the seat post. This ensured the cyclist did not adjust their position on the saddle to minimize the changes associated with different saddle setbacks.⁴ For each of the three setback conditions (randomised order), participants were instructed to perform a three-minute trial while keeping cadence (90rpm) and power (200W) constant using visual feedback. Only the last 30 seconds of pedalling were analysed, normalised to pedalling cycle, and averaged. A minimum of three minutes of active recovery rest at freely chosen power and cadence between trials was given to the participants to avoid any confounding effect of fatigue.

Data analysis

Similarly to Hamill's study, markers’ data served as input to the model for the computation of joint angles, ITB strain, strain rate and ITB-LFE compression force.¹⁶ The calculation of ITB strain and strain rate resulted from the recommended OpenSim calculation steps: 1) the model (i.e. segment lengths, mass distribution, muscle attachment sites) was scaled to match each participant's anthropometry based on experimentally measured markers placed on anatomical landmarks and location of joint centres individualised using a functional method; 2) joint angles were calculated with a global optimization-based inverse kinematics procedure; 3) ITB strain and strain rate were calculated as ITB length (meters) and lengthening/shortening velocity (meters per second), respectively, based on joint angles and moment arm at each degree of freedom.^29,32,33

A constant unit (1 Newton) ITB force was set for all participants and conditions. ITB-LFE compression force was calculated as the norm of the resulting LFE-femur joint reaction force component perpendicular to the sagittal plane of the femur and expressed as a percentage of ITB force.

Similarly, ITB-LFE force was computed for all combinations of hip and knee joint angles with the same procedure. Three participants were chosen to illustrate the potential influence of individual pedalling technique on ITB-LFE force.

Statistical analysis

Skewness, kurtosis, and the Shapiro Wilk test were used to establish data normality. All variables were normally distributed (Shapiro Wilk test p-value > 0.05, skewness between -2 and +2 and kurtosis between -2 and +2). A one-way analysis of variance (ANOVA) with repeated measures was performed on peaks of all hip and knee joint angles and on ITB strain, strain rate, and compression force. Subsequent post hoc analyses (Tukey least difference multi-comparison test) were used to determine significant differences among setback condition. All data are presented as mean ( ± standard deviation).

RESULTS

First it was verified that instructions were followed by the subjects. The 10% variation of saddle setback resulted in an average value of 29.60 ± 3.3 cm in the backward saddle condition and 23.75 ± 3.7 in the forward saddle condition (∼6 cm change).

There was no effect of saddle setback on peak of hip joint angles and peak of knee external/internal rotation. There was a significant effect of saddle setback on the peak of knee flexion/extension angle (p < 0.05) such that in the backward condition, the peak knee extension angle (37.5 ± 11.8 °) was lower than in the forward condition (39.9 ± 10.5 °). In other words, there was a 7% difference in knee flexion angle between the two extreme saddle setback conditions. ITB strain, strain rate, and compression force are illustrated in Figure 2. There was no effect of saddle setback on the peak ITB strain and strain rate (p = 0.8 and p = 0.25, respectively, Table 1). The peak of ITB strain and strain rate were 0.53 ± 0.03 m and 0.23 ± 0.04 m.s⁻¹ (average across all three conditions), respectively. The peak of ITB strain occurred around 194.1 ± 3 ° of pedalling cycle (e.g shortly after the bottom dead center), simultaneously with the time of the peak of hip extension angle (Figure 2). There was a significant effect of saddle setback on the peak compression force (p < 0.05) such as in the backward condition, peak compression force (5.05 ± 1.85 % of ITB force) was greater than in the forward condition (4.67 ± 1.74 %) (p < 0.05). These results are reported in Table 1. The time of peak compression force occurred at 150.3 ± 2 ° of the pedalling cycle simultaneously with the peak of knee extension (39.1 ± 11.1 °, mean across participants and conditions).

Figure 2.

Iliotibial band (ITB) strain, iliotibial strain rate, compression force between iliotibial band and lateral femoral epicondyle (ITB-LFE), hip and knee flexion angle. Black line represents the mean across all participants, conditions and cycles. Vertical dotted grey line and blue dashed line highlight the peak of hip extension (flexion is positive) and the peak of knee extension respectively (0 ° corresponds to maximal knee extension) during the pedalling cycle.

Table 1.

Peak (mean ± SD) of the iliotibial band (ITB) strain, the iliotibial band (ITB) strain rate and the compression force between iliotibial band and lateral femoral epicondyle (ITB-LFE) observed while pedaling in the three saddle setback conditions: backward, recommended, and forward.

Peak / Conditions	Backward	Recommended	Forward	p-value
ITB strain (m)	0.53 ± 0.02	0.52 ± 0.02	0.53 ± 0.02	p = 0.8
ITB strain rate (m.s−1)	0.23 ± 0.02	0.24 ± 0.02	0.23 ± 0.03	p = 0.25
Compression force (N)	5.05 ± 1.85	4.98 ± 2.06	4.67 ± 1.74*	p < 0.05

^*Significantly different from backward

Results of the simulation showed that the intensity of compression force was higher when the hip was extended and adducted (Figure 3) and when the knee was extended and internally rotated (Figure 4). One pedalling cycle of three cyclists (using their own preferred bike setup) is also drawn to illustrate the importance of individual pedalling technique. Maximal hip extension was 40 °, 55 ° and 70 °, maximal adduction was -15 °, -10 ° and -5 °, and the maximal compression force was 11%, 6%, and 3 % for participants 2 (solid black), 5 (dashed white) and 8 (dotted grey), respectively. Maximal knee extension was -20 °, -40 ° and -70 °, maximal knee internal rotation was 8 °, 1 °, and -3 ° (external rotation), and maximal compressive forces was 2.8%, 2.6%, and 2.4%, respectively.

Figure 3.

Simulated compression force between the iliotibial band and the lateral femoral epicondyle (ITB-LFE) (Newton) for combined knee flexion/extension [35, 110 °] and abduction/adduction [-20, 10 °] angles. Solid black, dashed white and dotted grey lines illustrate the kinematics of participant 2, 5, and 8 respectively.

Figure 4.

Simulation compression force between the iliotibial band and the lateral femoral epicondyle (ITB-LFE) (Newton) for combined knee flexion/extension [-140, 0 °] and external-internal rotation [-20, 20 °] angles. Solid black, dashed white and dotted grey lines illustrate the kinematics of participant 2, 5, and 8 respectively.

DISCUSSION

Researchers have suggested that saddle setback might have an influence on the occurrence of ITBS, but to date, no experimental study had demonstrated a link between saddle position and biomechanical determinants.^1,3,7 Therefore, this study offers an original approach to investigate the putative underlying mechanisms of ITBS and their association with bike setup and pedalling technique.

Kinematics (increased knee joint flexion and/or hip joint abduction) was proposed as being related to ITBS but no link had been established with the putative biomechanical determinants of ITBS put forward by researchers. Using a musculoskeletal model, the method developed here brings new interpretation of kinematic data related to cycling.

Significant changes were found in knee flexion angle in a way that decreasing saddle setback (moving the saddle closer to the handle bar) limited minimal flexion angle of the knee joint. Despite being statistically significant, the differences between the two extreme conditions were small (∼3 °). This is likely due to the fact that adjustment of saddle setback was limited (6cm) to remain realistic with changes that cyclists may actually do. Similarly, Bini's study reported a ∼5 ° difference in knee joint angle associated with a 9 cm amplitude change (tracked using a reflective marker fixed on the sacrum) in sitting fore-aft position.³⁴ Previous studies reported that bike adjustments of professional cyclists are very small and lead to limited changes in aerodynamics as well.³⁵ However, those limited changes can make a difference on the overall performance and may similarly have a significant effect on injury risk.³⁶

Although ITB strain and strain rate were suggested to be related to ITBS in runners in a similar study, the current results did not reveal any influence of saddle setback on those parameters. Hamill's study compared runners suffering from ITBS against a control group and found that runners with ITBS exhibited a greater ITB strain and strain rate.¹⁶ This discrepancy likely origintates from the different kinematics observed in running vs. cycling. Also, in the current study, a constant unit (1N) ITB force was prescribed instead of using a static optimization or electromyography-driven approach as used by Hamill and Miller. This modelling choice was made to focus solely on the influence of kinematics. This is a limitation as in reality ITB force is not constant across the pedalling cycle but this also dismisses uncertainties brought by the estimation of ITB force from inverse or forward dynamics.^16,17,37 Overall, the significant effect of saddle setback on ITB-LFE force supports the idea of compression force being a biomechanical determinant of ITBS and confirms previous studies by Falvey et al. and Fairclough et al.^14,15 Moreover, maximal compression force occurred when knee flexion was minimal, i.e. approximately 30 °, which corresponds to the joint posture that exacerbates pain in patients with ITBS.^{7,12,14,15,38}

In order to better understand the combined influence of hip and knee joint angles on compression force, ITB-LFE force was computed for all possible combinations of joint angles throughout the ranges of motion observed in cycling. The simulation revealed a strong influence of knee rotation, for example, 30 degrees of knee flexion combined with 10 degrees of internal (or external) rotation increased compression force by 24% compared to 0 degree rotation. Hip joint angles have a stronger influence: for example, 40 ° hip flexion (minimum flexion observed during a pedalling cycle) combined with 10 ° adduction increases compression force 100% compared to 40 ° flexion associated with a 10 ° abduction. The kinematics of three participants were drawn over the simulation graphs to illustrate this finding and show, for example, that participant 2 (solid black line) might be at a greater risk of developing ITBS than the other two. This participant had indeed a smaller hip adduction - which is beneficial - but this was counteracted with potentially detrimental higher hip extension and knee internal rotation that lead to an overall greater ITB-LFE compression force. As illustrated here, large inter-individual kinematic differences were found on all degrees of freedom. Therefore, individual pedalling technique, more than saddle setback, could be related to injury risk.

Limitations

Several limitations of the present study should be noted. Most importantly, there were no direct measures of strain, strain rate, or compression force. Each of these parameters were determined based on a model driven by the 3-D kinematics that were used as input into the model. Validation of these data would be difficult without invasive instrumentation placed within the ITB. Most of the modelling method was previously published and despite the numerous parameters accounted for, it cannot reproduce all the complexity of ITB attachments on the femur and tibia. Also, the model accounts for an individual's anthropometry (e.g. segments length, natural knee varus/valgus), but it does not address specific anatomical variations that may exist such as muscle imbalances or abnormal iliotibial band width or length which could exacerbate symptoms.¹⁴

There is no consensus of opinion regarding best practice in the treatment of ITBS.¹⁴ Conservative therapy, including rest, cryotherapy, stretching exercises, etc. and the use of anti-inflammatory medications, has been effective in helping athletes return to full competition, but they still miss much time in their sport (4-6 weeks) and the risk of re-injury is high. Complementary to these treatments, and given the limited influence of pedalling technique, this study strongly encourages the correction of individual pedalling technique from feedback on the whole lower limb kinematics rather than to limit to bicycle adjustments. In this perspective, physical therapy may also be useful to identify and improve limited ranges of motion (e.g. hip flexion). The simulation also offers biomechanical evidence for the potential use of stretching and strengthening exercises which could help minimize abnormal knee internal rotation and hip adduction.

CONCLUSION

The combined experimental-simulation approach developed in this study provides new insights into the pathomechanics of ITBS in cyclists and supports the hypothesis that compression force between ITB and LFE may be a leading cause. Saddle setback and more importantly individual pedalling technique seem to play a critical role. Further studies may include longitudinal investigation of knee pain before and after pedalling kinematics correction to confirm these findings. Finally, in the context of bike fitting, this study offers a valuable tool to help identify and correct potentially harmful sport techniques and optimize equipment setup/design.

Appendix 1. Description of Marker set.

Ind	Name	Placement	Related segments
1	R.ASIS	Right anterior-superior iliac spine	Pelvis
2	L.ASIS	Left anterior-superior iliac spine	Pelvis
3	R.PSIS	Right posterior-superior iliac spine	Pelvis
4	L.PSIS	Left posterior-superior iliac spine	Pelvis
5	R.Thigh.Front	Right front marker of the thigh	Right Thigh
6	R.Thigh.Upper	Right greater trochanter coordinates	Right Thigh
7	R.Thigh.Lateral	Right lateral marker of the thigh	Right Thigh
8	R.Thigh.Lower	Right lower marker of the thigh	Right Thigh
9	R.Knee.Lateral	Right lateral femoral epicondyle	Right Thigh
10	R.Knee.Medial	Right medial femoral epicondyle	Right Thigh
11	L.Thigh.Front	Left front marker of the thigh	Left Thigh
12	L.Thigh.Upper	Left greater trochanter coordinates	Left Thigh
13	L.Thigh.Lateral	Left lateral marker of the thigh	Left Thigh
14	L.Thigh.Lower	Left lower marker of the thigh	Left Thigh
15	L.Knee.Lateral	Left lateral femoral epicondyle	Left Thigh
16	L.Knee.Medial	Left medial femoral epicondyle	Left Thigh
17	R.Shank.Front	Right tibial tuberosity	Right Leg
18	R.Shank.Upper	Right fibula head	Right Leg
19	R.Shank.Lateral	Right lateral marker of the shank	Right Leg
20	R.Shank.Lower	Right inferior marker of the shank	Right Leg
21	R.Ankle.Lateral	Right lateral tibial malleolus	Right Leg
22	R.Ankle.Medial	Right medial tibial malleolus	Right Leg
23	L.Shank.Front	Left tibial tuberosity	Left Leg
24	L.Shank.Upper	Left fibula head	Left Leg
25	L.Shank.Lateral	Left lateral marker of the shank	Left Leg
26	L.Shank.Lower	Left inferior marker of the shank	Left Leg
27	L.Ankle.Lateral	Left lateral tibial malleolus	Left Leg
28	L.Ankle.Medial	Left medial tibial malleolus	Left Leg
29	R.Heel	Right posterior calcaneus	Right Foot
30	R.Toe.Med	Right 1st distal metatarsal head	Right Foot
31	R.Toe.Lat	Right 5th distal metatarsal head	Right Foot
32	R.Midfoot.lat	Right 5th proximal metatarsal head	Right Foot
33	R.Midfoot.sup	Right front part of the foot	Right Foot
34	L.Heel	Left posterior calcaneus	Left Foot
35	L.Toe.Med	Left 1st distal metatarsal head	Left Foot
36	R.Toe.Lat	Left 5th distal metatarsal head	Left Foot
37	L.Midfoot.lat	Left 5th proximal metatarsal head	Left Foot
38	L.Midfoot.sup	Left front part of the foot	Left Foot