What about uphill cycling biomechanics?

Tour de France (TdF) 2017 includes 21 stages raced in 23 days (with two resting days). Since its first stage, an individual time trial, to the last, a 103 km ride with the famous finish on the Paris Champs-Élysées, cyclists will fight for the yellow jersey (maillot jaune). In my first post here for WheelPower Training, I will talk about a decisive challenge during the TdF and other tours: the hills.

Cycling races have different configurations. In the tours, time trials stages are raced under steady-state conditions. Shorter time trials are raced on average at intensities close to the onset of blood lactate accumulation, while longer ones close to the individual lactate threshold. Mass-start stages are raced at low mean intensities, but are intermittent, with cyclists spending on average 30 to 100 minutes at, and above lactate threshold, and 5 to 20 minutes at and above the onset of blood lactate accumulation [1]. Climbs are included in some mass start stages, with longer distances going uphill followed by downhill segments placed at different moments of the stage. Considering this, here are two main points of my discussion: what are the main biomechanical changes while cycling uphill? Will the moment of the stage/race where hills happen influence cycling strategy/ technique?

Despite all strategic interplay among teammates that we know to be decisive in the results, what does science tell us about the biomechanics of pedaling uphill? Can the biomechanics of pedaling help us to better prescribe, monitor, and assess cycling performance?

Uphill cycling requires a higher torque production (i.e. 26-42% higher torque than while cycling on flat) [2]. With this higher torque demand, to sustain the target power output it is fundamental to control pedaling cadence. Back in 2008 we showed the importance of the preferred pedaling cadence being sustained despite of changes in the exercise workload to maintain pedaling effectiveness [3]. This higher demand for torque output on hills has an impact on exercise intensity, especially when the cyclist is standing [4]. The standing posture increases energy expenditure but is known also to add more power output. However, pedaling cadence invariably drops when standing, which means that power output will rely more on the magnitude of torque applied to the cranks. It is one of the factors that helps us to explain why a standing posture during uphill is not so common among professional cyclists, except – of course – when attacking or responding to an attack in the peloton. Standing posture impairs the technique and can progressively decrease efficiency if sustained for too long.

The higher torque and power output required while climbing comes at a cost for the cyclist: The change in body position and the higher demand of force modify the time and magnitude of activation of many leg and hip muscles, being the most affected those that cross the hip joint and tibialis anterior [5]. For instance, an 8% incline elicits higher pedaling effectiveness between crank angles of 45° and 225°, which are not the same case for more moderate slopes (ranging between 0% and 4%); this means that muscles will have to produce higher forces at lengths they are not used to.  By increasing slope, the onset of muscle activation (start of activation) will tend to happen earlier, but the offset will remain mostly unchanged, which means that muscles are activated for a longer period as slope increases. Longer activation time results in a higher metabolic demand, which impairs cycling efficiency and pedaling technique [6]. Interestingly, uphill cycling increases activation of calf muscles, which are known not to be very responsive to changes in workload on flat courses [7].

These aforementioned changes in pedaling biomechanics during uphill help us to understand why uphill is so challenging for the cyclists. Nevertheless, there many other factors to be considered that can make uphill cycling even harder. Mountain passes are highly demanding and intensity is related not only to the difficulty of the ascents but also to its moment within the stage [8]. The number and interconnections of al challenging factors during a mountain pass can be puzzling, but in a nutshell: exercise intensity at mountain passes varies depending on the cyclist  position in the stage and race. Intensity can be higher during mountain passes at the ‘end’ and/or ‘middle’ compared to the ‘beginning’ of a stage. Intensity during “OFF”  and “FIRST” category climbs are normally greater in the ‘middle’ than at ‘end’ of a stage. Itensity also varies according to race strategy since riders competing for the first  position (overall classification)  have to try to stay near the front group all times, and also keep as many teammates as possible with them. These teammates will support the leader driving the pace and controlling the rival teams especially in ‘middle’ and at  ‘end’ of the mountain pass. At this point, the leader should attack or respond to attacks strongly at end of the stages, trying to gain or not to lose time against the main rivals (overall classification not necessarily the stage classification). At the ‘end’ phase, only the leader and one or two very strong teammates will probably be still pushing hard, the remaining will tend to slow down once their support job is done [8].

Note: details of climb classification mentioned [8]: OFF category – uphill with a distance of at least 10 km and average slope of 8% or higher, and those with a distance and slope of at least 20 km and 6%; FIRST category – those longer than 6 km and slope of at least 7%, and those longer than 10 km and slope of 5%; SECOND category – longer than 7 km with a slope of 5%, and longer than 11 km with a slope of 3%.

In summary, cycling uphill is challenging because it changes the way force and torque are applied to the pedals, increases magnitude and time of activation of lower muscles, changes the pattern of the muscle activaiton, requires a strict control of pedaling cadence to sustain the power output, and compromises efficiency. A standing posture should be avoided for as long as possible since it affects cadence and increases energy expenditure. Pedaling cadence uphill must be as close as possible of the preferred pedaling cadence the cyclists are used to pedal as such a cadence will elicit the best pedaling effectiveness. Finally, the moment of the stage a climb will come will influence the strategy to takle it.

Coaches need to be able to integrate a large amount of information when planning training for uphill cycling. Furthermore, power output assessment in lab setups must consider not only absolute power output during maximal incremental laboratory tests but also the power to mass ratio, as a lighter body weight will play a fundamental role in the power output – consequently speed – during climbs.

References

[1] Mujika I, Padilla S. Physiological and performance characteristics of male professional road cyclists. Sports Med. 2001;31(7):479-87.

[2] Bertucci W, Grappe F, Girard A, Betik A, Rouillon JD. Effects on the crank torque profile when changing pedalling cadence in level ground and uphillroad cycling. J Biomech. 2005 May;38(5):1003-10.

[3] Rossato M, Bini RR, Carpes FP, Diefenthaeler F, Moro AR. Cadence and workload effects on pedaling technique of well-trained cyclists. Int J Sports Med. 2008 Sep;29(9):746-52

[4] Millet GP, Tronche C, Fuster N, Candau R. Level ground and uphill cycling efficiency in seated and standing positions. Med Sci Sports Exerc. 2002 Oct;34(10):1645-52.

[5] Sarabon N, Fonda B, Markovic G. Change of muscle activation patterns in uphill cycling of varying slope. Eur J Appl Physiol. 2012 Jul;112(7):2615-23

[6] Arkesteijn M, Jobson SA, Hopker J, Passfield L. Effect of gradient on cycling gross efficiency and technique. Med Sci Sports Exerc. 2013 May;45(5):920-6.

[7] Carpes FP, Diefenthaeler F, Bini RR, Stefanyshyn D, Faria IE, Mota CB. Does leg preference affect muscle activation and efficiency? J Electromyogr Kinesiol. 2010 Dec;20(6):1230-6.

[8] Padilla S, Mujika I, Santisteban J, Impellizzeri FM, Goiriena JJ. Exercise intensity and load during uphill cycling in professional 3-week races. Eur J Appl Physiol. 2008 Mar;102(4):431-8.