Saddle setback in cycling refers to the horizontal distance between the centre of the bottom bracket and the front tip of the saddle. Over the past few decades two principle methodologies for determining optimal saddle setback have emerged in the bike fitting community. The more traditional method, know as ‘Knee Over Pedal Spindle’ (KOPS), proposes that optimal saddle setback occurs when the tibial tuberosity is directly over the pedal spindle when the crank arm is at 90 degrees in the downward stroke. This methodology has been championed by Burke & Pruitt (2003) who have published widely in the scientific and cycling press.
More recently, KOPS has come under attack in the popular cycling literature on the grounds that it has no sound physiological and/or biomechanical foundation. An alternate methodology known as ‘Centre of Gravity’ (COG), originally proposed by Bontrager (1998), and given voice by well-known bike fitting commentators such as Steve Hogg, has recently gained considerable traction in the bike fitting community. Using COG, the optimal saddle setback is said to occur when the rider is well balanced and does not have to expend excessive muscular energy to support their weight (Bontrager 1998).
The purpose of this article is to evaluate the two principle methodologies used by bike fitters to determine optimal saddle setback. This paper will be published in three parts. Part 1 seeks to determine the validity of the key supporting arguments put forward by the proponents of KOPS by exploring the published research as well as the relevance of other related kinematic variables in determining saddle setback. Part 2 examines the validity of the theoretical foundation of the COG methodology as well as practical considerations in its application and issues in measurement accuracy. And finally, Part 3 deals with other relevant factors in determining saddle setback such as saddle comfort, frame geometry, Union Cycliste Internationale (UCI) regulations and cycling discipline. A summary of the key findings of the series is also provided to help guide best practice in determining optimal saddle setback.
Proponents of KOPS put forward two main arguments. Firstly, that in order to get maximum power from the pedals, the knee’s centre of rotation, in this case given as the patella-femoral joint (PFJ), must be directly over the pedal spindle (e.g. Pruitt 2006). And secondly, that knee positions forward of the pedal axis may result in higher PFJ compressive forces, leading to an increased incidence of overuse injuries (e.g. Wanich et al. 2007). However, very little evidence in the scientific literature can be found in support of these assertions.
In regards to power generation and performance optimisation, the scientific literature has focused on the relationship between seat tube angle (STA) and cycling performance, not KOPS. STA is defined as the position of the seat relative to the crank axis of the bicycle (Price & Donne 1996). However, there is no published research that compares STAs with KOPS positions. This leaves us with observation, anecdote and expert opinion. Accordingly, it would appear that KOPS for the majority of cyclists is typically achieved at an STA of between 72 to 74 degrees. The exact relationship between STA and KOPS may be of limited utility as much of the research on the effect of STA on cycling performance is in dispute.
One of the factors contributing to this apparent lack of clarity is the difficulty in isolating the effects of specific variables from each other, such as trunk angle, when researching the influence of STA on cycling performance. Of the studies that have used a research protocol that attempted to control for all relevant kinematic variables, it was found that STA was not a significant factor influencing cycling performance (Caddy et al 2015; Jackson et al 2008; Rankin and Neptune 2010). One explanation for this is that pedaling profiles change at different STAs. Research has shown that at steeper STAs, peak pedal forces occur later in the pedal cycle (Caddy et al. 2015; De Groot et al. 1994) and a clockwise shift in pedal angle is observed (Rankin and Neptune 2010; Browning et al. 1992).
That said, it has been suggested by researchers and practitioners alike that the utility in altering STA may come more from the effect on hip angle (HA), rather than the vertical relationship between the knee and pedal (e.g. Carver 2017; Hunter et al. 2003; Savelberg et al. 2003). Indeed research has shown that optimal muscle force production occurs within a certain range of muscle lengths and therefore within a range of joint angles (Rassier et al. 1999). In terms of aerodynamic considerations, there is general agreement that for a given trunk and knee angle, a steeper STA will result in a more open HA, thereby allowing cyclists to potentially improve aerodynamics without impacting hip kinematics (e.g. Caddy et al. 2015; Rankin and Neptune 2010). However, the effect of HA on power production and efficiency is not so clear.
While much of the research indicates that more open hip angles are associated with improved efficiency (Chen et al. 2015; Garside and Doran 2000; Heil et al. 1995; Price and Donne 1997; Ricard et al. 2006), other research has shown little or no correlation (Bisi et al. 2012; Heil et al. 1997; Rankin and Neptune 2010). One important pattern that does emerge from the research is that extreme positions of slack STAs (e.g. 70o and below) and/or low trunk angles (e.g. 20o and below), resulting in very closed hip angles, are associated with decreased efficiency (e.g. Gnehm et al. 1997; Heil et al. 1997; Heil et al. 1995). That aside, unlike the knee joint, optimal HA ranges to guide best practice in bike fitting have not been established. There are a number of reasons why this gap in the literature exists.
Firstly, the inconsistency with which HA is measured. In much of the literature, as well as in bike fitting practice, HA is defined as the angle formed between the femur and trunk in the sagittal plane (e.g Carver 2017; Heil et al 1995; Umberger et al 1998), hereafter referred to as HAa. The other less common, but more biomechanically correct way that HA is defined is the angle formed between the femur and pelvis, hereafter referred to as HAb (e.g. Bisi et al. 2012; Price and Donne 1997) and sometimes referred to as pelvis orientation (e.g. Dorel et al. 2009). While research has shown that changes in trunk angle influence muscle recruitment and joint kinematics in the lower limb (Dorel et al. 2009; Savelberg et al. 2003), in theory HAb should have a more direct impact on the power producing capabilities of the muscles that cross the hip joint that are important in generating propulsive forces in cycling, such as the gluteus maximus, rectus femoris and biceps femoris (Korff et al. 2017; Rassier et al 1999).
Secondly, the relative difficulty in manipulating HAb, as compared to, the knee angle. Anecdotally, in a bike fitting setting where positional changes are limited, HAb seems to be as much influenced by the relative strength and length of the muscles that cross the hip joint as it is by positional interventions, such as changes in handlebar position. Research by Bisi et al. (2012) supports this observation. In a study of trained triathletes they found that the effect of positioning the saddle closer to handlebars was compensated by changes in trunk inclination and not HAb.
And finally, the effect of long-term training on the muscle length and force production relationship (Savelberg and Meijer 2003). For example, Heil et al. (1997) found that oxygen uptake was optimised at HAa that corresponded to the subjects preferred HAa from their own bicycles. Hence, it seems that optimal hip angles may be as much a functional of individual musculoskeletal strength and mobility as well as training, as it is a range that can be applied across the general cycling population. More research isolating the specific effects of HAa and HAb on power production and efficiency in trained and untrained cyclists is needed before any definitive conclusions can be made.
There are a number of scientific papers and popular literature publications that suggest that knee positions forward of the pedal spindle when the crank is at the 3 o’clock position may increase the risk of patellofemoral joint (PFJ) pain (e.g. Callaghan 2004; Pruitt 2006; Silberman et al. 2005; Wanich et al. 2007). However, none of this literature has provided an explanation as to why this may be the case or evidence to support these claims. When it comes to PFJ pain in cycling, modeling of knee kinematics has shown that for a given knee extensor muscle force, patellofemoral compressive forces increase with an increased knee flexion angle (Ericson and Nisell 1987; Nisell and Ekholm 1986), which in turn may lead to an increase risk of knee overuse injuries (Neptune and Kautz 2000).
At steeper STAs, knee flexion angles when the crank is at the 3 o’clock position would be greater. To illustrate this point, consider the following example. If a cyclist were able to pedal in a prone position, knee flexion would be close to its maximum with the crank at 3 o’clock. One might argue then, that if, as many proponents of KOPS believe, peak pedal and knee extensor muscle forces occur at the 3 o’clock position (e.g. Pruitt 2006), patellofemoral compressive forces would be larger. However, as mentioned previously, research has shown that at steeper STAs peak forces occur later in the pedal cycle (Caddy et al. 2015; De Groot et al. 1994). Therefore, so long as the appropriate increase in saddle height is made to accommodate the change in saddle setback to maintain optimal knee flexion/extension angles, the fore/aft position of the saddle should be of little consequence. The epidemiology of PFJ pain in cyclists and triathletes supports this thinking. Bini and Di Alencar (2014) observed that research has shown that triathletes, who typically opt for saddle position that results in a ≈6cm forward projection of the knee compared to ≈2cm for road cyclist, do not have a greater occurrence of overuse knee injuries as compared to road cyclists.
In summary, it would seem that the key arguments that the KOPS methodology is built upon is not supported by the research. The scientific evidence suggests that the effect of saddle setback on HAa and/or HAb, rather than the position of the knee over the pedal has a greater impact on cycling performance, particularly in aerodynamic positions. Furthermore, in terms of saddle position, saddle height rather than setback play a greater role in minimising patellofemoral compressive forces and hence the risk of injury.
Part 2 of this series, due for release early in 2018, will discuss the COG methodology for determining saddle setback, a protocol that focuses more on rider comfort than performance.
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