Easy rider: how to cycle for better run performance

How can biathletes, dualthletes and triathletes optimally balance pace and effort between the cycling and running legs for maximum overall performance? SPB looks at the research

Cross training, whether for general fitness or to compete in events such as biathlon, duathlon and triathlon (see box 1) offers a number of physiological advantages. First of all, being able to alternate training modes creates a more balanced loading on the muscular system, which is less likely to lead to muscle strength imbalances and (as a consequence) injury. Secondly, varying your training allows athletes to work the cardiovascular system more extensively with less chance of localised muscle overload. For example, after a hard swimming workout, you’re still quite fresh to run or bike because the main muscle groups utilised in swimming are not significantly involved in activities such as running or cycling. The of course, there’s the very important issue of boredom; doing the same activity, day in, day out, is much less mentally stimulating than performing a variety of activities, and is much more likely to lead to boredom and even staleness.

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Box 1: Popular ‘cross-training’ endurance sports

 Biathlon - Officially, a biathlon event consists of a mixture of running and shooting, and is thought to be symbolic of the enduring challenge faced by primitive man – to chase down and kill/capture prey. However, modern biathlon is effectively a kind of cut down triathlon, with the swimming excluded – ie consisting of running and cycling. Although not as ‘all round’ a cross training event as triathlon, this type of biathlon has become popular because it still provides cross-training challenges and benefits, it appeals to non-swimmers and races are easier to stage - ie without the logistics and safety concerns that swimming involves.

Triathlon - (swimming, cycling and running) is perhaps the classic cross-training combination. The first documented triathlons were organised as offbeat training routines for runners back in 1974 by the San Diego Track Club, but the event really caught the public’s imagination with the advent of the Hawaiian Ironman Triathlon four years later. Although it took a while for triathlon to develop into a mainstream sport, runners, swimmers and cyclists from all backgrounds began to realise that including small amounts of the other two disciplines could actually help their main sport by helping to overcome any muscle imbalances and also by enabling cardiovascular training to be continued, while resting the main muscles used in their own sport.

Duathlon is an athletic event that consists of two disciplines (running and cycling) but with three legs: a running leg, followed by a cycling leg and then another running leg in a format similar to triathlons. In a sense then, duathlons are most similar to triathlons, with the key difference being the replacement of the swimming leg with a second run. The standard duathlon distance consists of a 10km run, 40km bike and a second 5km run. Sprint distance duathlons entail a 5km run, 20km bike and a 2.5km run, while long distance duathlons are typically 10km runs followed by a 150km bike leg then a second run of 30km. A popular variation of a duathlon is an off-road duathlon. This entails a trail-running stage and a mountain-biking stage, finishing with a final second trail-running stage. Off-road duathlons differ from their road counterparts in that the terrain is typically rough, uneven and very hilly, with little or no tarmac paving.

Decathlon/heptathlon The decathlon is a 2-day 10-discipline track and field event, which demands comprehensive all round athletic ability. Day 1 comprises of 100m, long jump, shot put, high jump and 400m, while day 2 entails a 110m hurdles, discus, pole vault, javelin and 1500m run. The women’s equivalent is the 7-event heptathlon comprising of (day 1) 100m hurdles, high jump, shot, 200m run and (day 2) long jump, javelin and 800m run. Both events are a supreme test of athletic ability because they demand superb endurance, speed, strength and skill, all of which have to be developed without detriment to each other!

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Cross training downsides

Of course, every silver lining has a cloud and cross-training sport is no exception! Probably the most important of these is the issue of ‘specialization’ – or rather the lack of it. In very simple terms, one of the key factors in determining the training effect is ‘specificity of training’. The concept of specificity means just that – any adaptation occurring as a result of exercise tends to be very specific to the training performed. In other words, to become a good swimmer, you have to do a lot of swim training – not biking or running.

In fact, the concept is even more specific (no pun intended) than that; if you want to become a good 200m freestyle swimmer, the best way to adapt is to perform a lot of 200m freestyle swimming sessions! As a rule of thumb, the specificity law of training favors single-sport athletes. For example, if your only activity is cycling, you’ll have the advantage of spending far more time developing the necessary motor skills/patterns and biochemical adaptations in the muscles used on the bike than say a triathlete, who has to divide their time across three disciplines of which two will be non-specific to cycling.

Cycling and running interference

Less training specificity is a challenge for those trying to reach peak performance in any one discipline. However, there’s a further confounding factor for a cross-training athlete – interference between disciplines. Although it’s a technically more demanding discipline, pacing the swimming leg of a triathlon is of relatively little consequence to the cycling leg that follows. That’s because during the action of swimming, the emphasis on the muscle groups involved is quite different. For starters, there’s a lot more upper body muscle recruitment - muscles that aren’t used in any significant way during cycling. Secondly, the lower body muscles that are used during swimming (legs and buttocks) are recruited through quite different ranges of movement compared to cycling. What this boils down to is that triathletes can swim pretty hard, and apart from the initial swim/bike transition period, subsequent cycling performance will be relatively unaffected.

Things are quite different however when it comes to pacing the subsequent biking leg because in cycling and running, there’s a much stronger overlap between the patterns of muscle recruitment. Both disciplines rely mainly on the calves of the lower leg, the quadriceps and hamstrings of the front and rear thigh respectively and of course the buttock muscles. Also, the ranges of muscle movement in both disciplines are not too dissimilar. Add these facts together and it’s easy to see how the effort invested in the cycling leg of a race can significantly affect an athlete’s subsequent running performance. An obvious question for biathletes and triathletes seeking to maximize their overall performance therefore is how best to train and pace the cycling leg to minimize the impact on running performance without losing too much time on the bike?

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The bike-run connection

It turns out that there’s not much research in this area. However, while only a few studies have been carried out, the results that have emerged are nevertheless intriguing. A comprehensive review of the differences in the physiological demands of cycling and running by Swiss scientists in 2009 (summarized in box 2) suggests that a subsequent bout of running is more likely to be affected by a previous bout of cycling than vice-versa⁽¹⁾ – ie the physiological effects of a cycling leg of a triathlon is very critical to subsequent running performance.

Meanwhile, other researchers have also found solid evidence that during periods of combined high-volume bike and run training, triathletes are by no means immune from injury and may even suffer from cumulative stress precisely because of the cross training nature of their sport⁽²⁾ (see box 3).

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Box 2: The bike-run connection

Why does cycling have such a profound influence on a subsequent run and what is the relationship between the two disciplines? Swiss researchers reviewed the evidence and concluded that the following factors were important⁽¹⁾:

• The increase in central nervous system fatigue that occurs after prolonged exercise has a bigger impact on subsequent running performance than cycling performance. This is because central nervous system (CNS) fatigue impairs coordination and running requires more coordination than cycling.
• It is likely that there’s more physiological training transfer from running to cycling than vice versa – ie each hour spent running in training could be more beneficial to overall triathlon performance than an hour spent cycling.
• The crouched down position means that ventilation is more impaired in cycling than in running, leading to higher concentrations of fatiguing lactate at lower rates of oxygen consumption. This could carry over into the running leg of a triathlon, impairing performance.
• Pedaling cadence affects the metabolic responses not only during cycling but also during a subsequent running bout – ie the way you cycle the bike leg can also impact run leg performance.

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Box 3: Bike-run training and injury risk

In a key study, researchers examined the training diaries of 50 top British Olympic Distance triathletes to see whether their swim, cycle and run training exerted a cumulative stress effect on the risk of overuse injury⁽²⁾. Each triathlete supplied diary data for a 7-month period and the duration and intensity of their training in each discipline was assessed. The researchers also looked to see how the training loads changed from week to week, and were particularly interested in the 4-week period prior to an injury occurring. When all the collected information was analysed, the results showed the following:

• Sixty percent of the triathletes reported at least one overuse injury, which resulted in a performance drop;
• The incidence of an overuse injury was related to the combined loading of cycling and running training performed at moderate to high-intensity two weeks before the onset of the injury.

The researchers concluded that ‘the extent to which cycle and run training have a cumulative effect on triathlon injury risk deserves further investigation’. What this means in practice is a) that high training loads in one discipline can significantly increase the injury risk in another and b) that it’s the total training load that determines an athlete’s injury risk. This means that simply cutting down training volume in one discipline (to reduce injury risk) and replacing it with more from another discipline won’t necessarily protect an athlete from injury in that first discipline!

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Meanwhile, an Australian study found solid evidence that central nervous system fatigue and motor control as a result of a prior bout of cycling play a significant role in subsequent running performance in triathletes⁽³⁾. In particular, they found that a 45-minute high-intensity bike session altered the patterns of muscle recruitment and movement during a subsequent run, particularly at the knee and ankle joints. One of the consequences of this altered muscle recruitment was a reduction in ‘running economy’ in the run that followed – ie compared to no prior cycling, the triathletes needed to consume more oxygen to maintain a given running pace (a bad thing!).

Transition training

In the study above, researchers theorized that the reduction in running economy following a prior bike session was due to altered motor recruitment patterns in the muscles. One question that arises from this is whether training for the bike/run transition can help to ‘teach’ the motor units firing the muscle fibers how to switch from cycling to running mode more efficiently, and so minimize the reduction in subsequent running economy. A 2004 study on elite junior and senior triathletes might provide some answers⁽⁴⁾.

Thirty-one elite triathletes competing at World Championship level (comprising of 7 junior males, 6 junior females, 9 senior males and 9 senior females) performed a laboratory trial, which consisted of sub-maximal treadmill running (to determine running economy), maximal and then sub-maximal cycle ergometry (to determine the peak power output peak power output and cycling economy). This was followed by an additional sub-maximal running bout. Swimming, cycling, running and overall race performance (min) over a standard event was also measured in the field. When the researchers compared the running economy of the triathletes pre-cycling and immediately post-cycling, they found (as expected) poorer running economy post-cycling. Interestingly however, the senior female triathletes showed no post-cycling drop in running economy and the senior males showed a smaller drop compared to the juniors. One possible explanation advanced is that the senior triathletes were much more practiced/experienced in bike/run transitions and had therefore been able to ‘train’ their motor recruitment systems to transition between disciplines more effectively.

Cycling intensity and running economy

There’s solid evidence that prior cycling does impact on subsequent running economy and an Australian study on triathletes found good evidence for a strong link between rate of perceived exertion (RPE – see table 1) during the cycling and subsequent running economy⁽⁵⁾. Running economy was compared between a control run (no preceding cycling) and a run performed after a 45-minute high-intensity cycle in eighteen triathletes. Power output, RPE and blood lactate concentration (a measure of biochemical fatigue) were monitored throughout the cycle test and the relationship between cycling intensity and the change in running economy was evaluated. The results showed that the triathletes' RPE at the end of their cycling bout was significantly associated with the change in running economy after cycling – the higher the average RPE during the cycle bout and RPE at the end of the cycling bout, the more impaired the running economy of the triathletes. The clear implication is that while you can shorten your bike leg time with high-intensity riding, push too hard and your running performance might suffer by a greater margin than the gains accrued from cycling hard!

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Table 1: Borg’s rating of perceived exertion table

NB: The description refers to subjective feelings. The number approximately corresponds to the heart rate divided by ten. Heart rates shown are approximate and will also depend on age.

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Lessons from duathletes

More evidence for the impact of prior bouts of different exercise on running performance were uncovered in a 2016 study on highly-trained duathletes⁽⁶⁾. In this study, researcher looked at the compounding effects of the initial run and cycling legs of duathlon simulation (carried out in the lab) on maximal oxygen uptake (VO2max), ventilatory threshold (VT – the point at which breathing rate increases disproportionately for a small increase in exercise intensity) and running economy (RE). To do this, seven highly trained multisport athletes completed three trials:

• Trial-1 consisted of an incremental treadmill run (to determine VO2max, VT, and RE) – ie to set a baseline for running performance when fresh.
• Trial-2 consisted of a 10km run at 98% of VT followed by an incremental VO2max test on the cycle ergometer – ie assessing the impact of the prior run on cycling performance.
• Trial-3 consisted of a 10km run and 30km cycling bout at 98% of VT followed by a speed only treadmill test – ie to determine the compounding effects of the initial legs of a duathlon on the final running leg.

The main finding was that there was no difference in VO2max, maximal heart rate or the perceived exertion at maximal pace in all three trials. A second finding was that VT was reached at the same oxygen consumption level during the bike session (trial 2) as the first run leg (trial 1). What this means is that a prior run seem to have minimal impact on subsequent cycling performance.

However, the previous run and bike sessions DID has a performance impact on the third run. A very significant drop in running economy was observed in the trial 3 (final run) compared to the initial run (see figure 1). In other words, more oxygen was required to sustain a given pace. As a consequence, VT occurred earlier and at a slower running pace – in short, breathing became harder and more labored at lower running speeds in the second run leg compared to the first run leg.

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Figure 1: Running economy in trial 1 vs. trial 3⁽⁶⁾

Running economy, expressed as a comparison of VO2 at each submaximal running speed during the incremental treadmill tests performed during Trial-1 and Trial-3. Arrows indicate the calculated ventilatory threshold for Trial-1 and Trial-3 respectively.

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Summary and practical implications

Although this is an area where more research is needed, the evidence to date suggests that the performance of cross-training athletes such as duathletes, biathletes and triathletes is significantly affected by the bike-run interface, both in training and in competition. Here are some practical applications of the latest research to help your cross-training performance:

• Include plenty of back-to-back bike/run sessions in your training (see this article). This will help your CNS to ‘become familiar’ with the changes in motor-firing patterns demanded by the bike-run transition.
• By contrast, there’s little evidence that performing back-to-back bike-run training sessions is a good time investment as the impact of prior biking on running appears minimal.
• Perform some regular lower body strength training to help combat CNS fatigue in the later running section of a race (see this article for tips).
• Practice honing your pedaling technique (avoid ‘pushing’ big gears) and riding posture on the bike to minimize the impact on subsequent run performance.
• When increasing your cycling load, back off a bit on the running (and vice-versa). You may risk injury if your total bike/run training load increases within too short a time frame.
• In competition, try to pace yourself on the bike, avoiding high RPEs (keep at 15 or below – see table 1) - to reduce the impact on your subsequent running economy. Push too hard on the bike and any time savings you make could be more than wiped out by increased run times!