What is the Evidence Behind Bike Fit ?

Cycling related pain and overuse injury is historically very common among cyclists. From a 1 year recall period cyclists reported complaints related to the neck (48.8 %), knees (41.7 %), groin/buttocks (36.1 %), hands (31.1 %), and back (30.3 %) (Wilber et al, 1995). Similarly high rates of complaints were found during bicycle tours related to the buttocks (32.8%), knee (patellar and IT band) (20.7%), neck-shoulder (20.4%), groin (10%), palm (10%) (Weiss et al, 1985), buttocks (42%), crotch (34%), upper leg (25%), neck (24%), knee (24%), hand or fingers (19%), shoulder (17%), foot or toes (17%), back (16%), wrist (8%), and lower leg (6%) (Dannenberg et al, 1996).

Percent of Cyclists With Complaints by Body Region

Wilber et al. 1995(1 year recall) Weiss et al. 1985(bike tour) Dannenberg et al, 1996(bike tour)
Neck 48.8 24
Neck/Shoulder 20.4
Shoulder 17
Wrist 8
Hand 31.1 10 19
Back 30.3 16
Buttock 32.8 42
Groin 10 34
Groin/Buttock 36.1
Upper leg 25
Knee 41.7 20.7 24
Lower Leg 6
Foot 17

The primary clinical intervention to treat/prevent cycling related pain is the bike fit. Bike fit is the process of optimizing the 3 dimensional configuration of the cleats, seat, and handlebars for the individual cyclist. Of the bike fit parameters, multiple authors agree that correct saddle height is not only important for knee injury prevention but for performance maximization as well (Obrien 1991, Asplund et al 2004, Holmes et al 1994, Shanner and Halloran 2000, Wanich 2007, Bini et al 2011). At the time of this writing, the most recent recommendations from a comprehensive review of the scientific literature recommends assessing appropriate saddle height by measuring knee angle at bottom dead center (BDC) and achieving a target range of 25-30 degrees flexion (Bini et al 2011). This recommendation is in line with the major commercial fit system recommendations of a 25-35 degrees knee angle at BDC (SICI 2007, Swift and Schoenfeldt). However, these recommendations are based on incomplete evidence (Bini et al 2011).

The initial recommendations for assessing appropriate saddle height are based adjustments to saddle height to match percentages of lower extremity (LE) measurements found to maximize performance parameters (Hamley and Thomas 1967, Shennum and deVries 1976, Nordeen-Snyder, 1977). Experimental evidence also demonstrates that changes in seat height relative to these LE measurements affects both tibiofemoral forces as well as patellofemoral forces (Ericson and Nissell (1986 and 1987). However, a limitation of this early work is that anthropometric measurement based methods result in a wide range of kinematic responses in terms of the knee joint angle achieved at the BDC (Peveler et al, 2005). More recent studies improve upon performance maximization using a target knee angle of 25 degrees BDC as compared to the traditional method (Peveler et al 2007, and Peveler 2008, Peveler and Green 2011). The use of a target knee angle at BDC to assess appropriate seat height is further supported by studies describing strong kinematic relationships between knee angle at BDC and large 4 – 10% changes in seat heights (Nordeen-Snyder 1977, Price and Donne 1997, Sanderson and Amoroso 2009). A recent 3D study, has confirmed the effect of smaller 2 cm seat height changes on hip, knee, and ankle kinematics (Puchowicz et al. 2013).

The major commercial fit methods of SICI and BIKEFIT also primarily use the 25 -35 degree knee angle at BDC to assess saddle height as part of a whole body optimization (SICI 2007, Swift and Schoenfeldt). Cyclists undergoing a bike fit are further instructed that they may need to adjust the seat up or down by up to 1 cm or approximately plus minus 1% of seat height to accommodate for individual comfort and functional status. While any change greater than this suggests there position is out of range and needs reassessment (SICI 2007). Interestingly, while the goal of seat height adjustment has been to alter knee flexion, the only kinematic study comparing cyclists with and without knee pain found no difference in knee flexion (Bailey et al. 2003).

Another focus of bike fit  theory is that knee pain is the result of  repetitive strain from shank abduction and subsequent medial motion of the knee in response to maximal loading during the powerphase of the pedal stroke(Francis 1988, Sanner and O’Halloran 2000, Hannaford et al 1986, Asplund et al 2004, Obrien 1991, Wanich et al 2007, SICI 2007, Swift and Schoenfeldt). Varus wedges mounted under the cleat are recommended as an intervention to support the medial column, decrease shank and knee motion during the power phase, and thereby reduce knee stresses and injury risk (Francis 1988, Sanner and O’Halloran 2000, Wanich et al 2007, SICI 2007, Swift and Schoenfeldt). Due to the presence of forefoot varus in 87% of normal people (Garbalosa et al 1994), it is has been suggested that the normal foot will collapse medially when called upon to act as a rigid lever in cycling (Swift and Schoenfeldt) and that the majority of cyclists would benefit from a  varus cleat wedge (Sanner and O’Halloran 2000, Swift and Schoenfeldt). Bike Fit Systems and Specialized both market plastic cleat wedges for this purpose (bikefit.com, specialized.com).

Francis (1988) put forward the the initial theory linking foot pronation, shank abduction, and knee injury. Based on theoretical modeling, his theory states that as the foot is loaded pronation results in shank abduction during the power phase of the pedal stroke, 30 to 150 degrees (Cavanagh et al, 1988), followed by the shank returning to a neutral position in the recovery phase as the foot is unloaded and pronation is no longer a factor. The power phase shank abduction is seen clinically as medial motion of the knee towards the top tube during the down stroke. The implication is that the normal non-driving moments acting on the knee (Davis et al, 1981, Ericson et al, 1984) would be increased. Effects would then be compounded by the interaction of varus/valgus moments with axial moments to produce more knee stress than either alone (Mills et al, 1991). This theory is supported by the finding that joint moments are significantly increased by forefoot varus, and that the shank follows the expected sequence of abduction during the power phase and adduction through the recovery phase (Ruby, 1992). Unfortunately, simply allowing multi degree freedom at the pedal is not effective in reducing joint moments (Boyd et al, 1997). Instead the authors conclude that pedal parameters needed to be adjusted on an individual by individual basis. Studies on injury are limited but increased medial lateral knee motion (Hannaford et al 1986) and increased shank abduction have been described in subjects with a history of knee pain versus controls (Bailey et al 2003) lending further support to the theory.

Attempts to correct shank abduction during the power phase using cleat wedges have been mixed. Sanderson (1994) found a position shift in lateral extreme of motion but no clear effect on range of medial lateral motion of the knee in response to varus and valgus wedges. Pilot data utilizing 3D analysis did confirm the positional shift, but from the frontal plane positional shift of the ankle center rather than changes in shank ab/adduction (Puchowicz et al. 2011).

In contrast to reductionist approaches to manipulating bike fit for the prevention or management of injury, the kinematic data as a whole suggests an integrated view is likely necessary. Although the seat is a fixed point relative to the bottom bracket the cyclists interaction with this contact point is not. During normal pedalling the hip translates forward and downward (Sauer et al 2007). Changes in hand position have been shown to affect pelvic tilt (Sauer et al 2007) and trunk lean is connected to ankle PF (Dingwell et al 2008). Additionally, knee ROM, knee flexion at BDC, ankle plantar flexion (PF) at BDC (Nordeen-Snyder 1977, Sanderson and Amoroso 2009, Price and Donne 1997, Puchowicz et al. 2013), hip rocking, and pelvic tilt (Price and Donne 1997) have all been shown to alter with changes in seat height. Similarly, kinematics are altered during static versus dynamic measurements, as well as with increasing load, and with fatigue (Peveler et al. 2012). Taken together, it is evident that the effect of any bike fit change, or musculoskeletal dysfunction is likely to be spread over several body segments functioning and dependent upon the dynamic state at time of measurement.

The interconnectedness of cycling kinematics as it relates to injury is reflected in the multi-point and overlapping bike interventions that are suggested for the variety of overuse injuries found in cyclists. Limiting this discussion to the lower extremity, 3 recent in depth reviews the following table illustrates the interventions suggested for each injury:

 

PatelloFem Patellar Tendinitis Quad tendinitis Pes bursitis Medial Plica IT Band Greater Troch Bursitis Iliopsoas tendinitis Achilles tenidinits Plantar Fasciitis Metarsalgia Hamstring strain
Move Cleat Back W ?W
Ext rotate cleat ?W ?W ?W ?W
Introtatecleat ?W W ?W W W,?S ?S ?W ?W
Varus Wedge W, ?S Wh ?W W ?S ?S ?S
Valgus Wedge ?W W,?S ?S
Orthotic W, ?S W W W, ?S ?S ?S
Move Saddle Forward ?W W,S S
Move SaddleBack W, T ?W W
Raise Saddle W, ?S, T, ?B ?W W W,S W
Lower Saddle ?S, ?W W, S W, S W S
Saddle Tilt
Saddle Rot
Saddle Shape
Shorten Bar Reach S S
Raise Bar W, S S
metatarsal button W
more flexible sole W

B = (Bini et al 2011), S = (Sanner et al 2000),  W = (Wanich et al, 2007). A letter indicates a suggested interventions, a “?” preceding a letter indicates an intervention to be evaluated.

Unfortunately, the vast majority of bike fit interventions suggested are supported only by anecdotal experience and have not been tested in a scientific manner. Experimental testing is of particular importance in areas of competing theories. For example, Sanner (2000) suggests that a high seat position increases medial lateral knee tracking due the greater difference in medial and lateral femoral condyle circumference engaged near full extension putting cyclists at risk for knee injury in contrast to the “common knowledge” that too low of a seat causes anterior knee pain due to increase patellofemoral compressive forces. Sanner (2000) goes on to note that his experience has shown VMO overdevelopment in cyclist with patellofemoral dysfunction perhaps as a compensation for poor bike fit/mechanics. Similarly, pilot data on the effect of cleat wedges failed to show changes in shank abduction during the powerphase with varus or valgus wedges (Puchowicz et al. 2011). Instead, the positional shift of the proximal shank previously found (Sanderson et al 1994) appeared to be the result of a symmetric shift of the entire shank across the pedal stroke (Puchowicz et al. 2011). This finding challenges the theory behind the use of wedges to decrease powerphase shank abduction (Francis 1988, Sanner and O’Halloran 2000, Wanich et al 2007, SICI 2007, Swift and Schoenfeldt). Such practice carries a risk of inappropriate varus wedging and potential exposure of the knee to increased varus moments (Wolchock et al 1998, Gregersen et al 2006).

The ultimate goal of bike fit should be to make fit interventions that reduce the risk of injury in a preventive manner as well as treat active disease. However, the current paucity of clinically relevant studies makes it difficult to know where to begin testing. At this point, the most logical point is with a thorough prospective investigation to identify cycling kinematic dysfunctions that correlate with injury risk. This information would allow the targeted testing of bike fit interventions ultimately setting the groundwork future clinical trials.

Conclusion:

Cyclists, due to the repetitive nature of the activity, are at extremely high risk for overuse injuries. A variety of bike fit interventions have been suggested to treat and prevent injury based on often competing and untested theories of kinematic dysfunction.

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