Triathlon training: improving the bike-run transition during competition

If you have ever competed in a duathlon or triathlon or even carried out a 'brick' workout, in which you shift quickly from biking to running, you will know how challenging the bike-run transition can be. Once you have left the relative comfort of your bike seat, those first running steps can feel awesomely difficult; your running pace will certainly be below par - and you may well wonder whether you will be able to finish the run portion of your competition or workout with any kind of quality at all.Why do your legs feel so leaden when you try to run after strenuous cycling? If you happen to be competing in an Olympic, middle- or long-distance triathlon, your leg muscles may well be somewhat glycogen-depleted after 40, 80, or 180k of strenuous cycling respectively. This glycogen depletion can cause significant fatigue, making your legs 'heavy' and unresponsive. When your leg muscles are low on glycogen, they simply don't have enough of the 'high-octane fuel' needed for fast running.

If you haven't stoked up on fluids properly during the bike stage, dehydration may also be taking its toll. But even when glycogen level and fluid intake are fine, there is another complication which can make you struggle: as you start the run phase of your bike-run transition, your nervous system is still geared towards controlling the mechanical movements required for cycling. It takes time for the brain and spinal cord to adjust to the completely new patterns of neuromuscular coordination needed for running, and during this adjustment period running feels sluggish and uncoordinated. This is an attractive explanation for the troubles experienced during the first few minutes of running after biking, especially since the muscles often begin to feel less fatigued after a few minutes, which would not happen if glycogen depletion or dehydration were the source of the fatigue.

There's also another intriguing explanation for the difficulties of running after cycling: the change from one activity to the other induces a redistribution of blood flow to the propulsive force-producing muscles in the legs(1). Thus, muscles that are activated more for running than for cycling may have to wait for a short period of time to receive augmented flows of blood. During this waiting period, they may be somewhat short of the oxygen (or fuel) required for high-intensity effort.

How bad are the drop-offs in capacity during the initial portion of the running stage of a triathlon? Recently French researchers found that 70% of national-level triathletes remained up to 10% below their average 10k running velocity over the first 500-1000m of the run phase, losing much valuable time in the process(2).

Why the bike-run transition is such a critical period

Such findings make an important point - and raise a couple of key questions. First, it's clear that the bike-to-run transition is a critical time during the triathlon, when much time can be gained or lost. Athletes who can preserve running ability during the transition will have a significant advantage over the majority of competitors, who have significant troubles with this stage of the race. The key questions then are:

a. How did some triathletes (up to 30%) manage to hang on to their usual 10k speeds during the run portion of the bike-run transition?
b. What training and racing strategies are best for enhancing the ability to manage the transition effectively?

To find out more about the problems associated with the bike-run transition and to develop techniques which might optimise performance during this key portion of a triathlon, British sports scientists Millet and Vleck studied the physiology and biomechanics of the transition in both junior and elite triathletes(3). They defined the 'cycle-to-run transition' as the period from the beginning of the last kilometre of the cycle section to the end of the first kilometre of the run, and the 'transition area' as the clearly demarcated area in which athletes dismount their cycles and begin running.

They begin their analysis by pointing out an obvious transition strategy - to reach the transition area at the head of a group, rather than in the middle or at the end of it, thus avoiding collisions and jams within the transition area. In fact, most experienced triathletes increase their speed during the final kilometre with this goal in mind - and often find, in doing so, that they have 'something left' at this stage. There is some evidence, though, that significant speed-ups over the last kilometre of the cycling stage may have a negative impact on performance during the first part of the running stage - on which more in a moment.

Although it represents just a small fraction of the total time required to complete a triathlon, time spent in the transition area is actually a fairly good predictor of finishing position and overall triathlon ability. For example, during the 1997 and 1998 Triathlon World Championship competitions, elite senior triathletes took an average of 56 seconds to traverse the transition area (less than 1% of the total time required to finish an 'Olympic' triathlon), while junior-level athletes took 83 seconds (1.1% of total time). Amazingly, the very best triathletes require less than eight seconds to rack their cycles, take off their helmets and put on their running shoes (and should be put to work immediately at nursery schools, teaching young children how to tie their shoes laces in fewer than the usual 20 minutes!) Millet and Vleck were able to show that the higher a triathlete is placed in the field toward the end of the cycling section, the greater the importance of transition area time to his/her final finishing position. Since top 10 finishing positions are gained or lost by seconds and even fractions of seconds, transition area skills are extremely important.

Transition-phase running is harder

Millet and Vleck summarised other studies documenting the physiological uniqueness of the bike-run transition - investigations which showed that transition-phase running really is harder than running on its own. Oxygen consumption, respiratory frequency, ventilation rate, and heart rate all tend to be higher during transition-phase running than during routine running at the same speed. In one study of 13 female duathletes and triathletes, running economy (the rate at which oxygen is used at a specific speed) was measured at running speeds of 169, 177, 196, and 215m per minute during control running (without prior biking) and also after 45 minutes of cycling at the rather modest intensity of 70% VO2max. In each case, running economy was worse (ie oxygen consumption rate was higher) after the biking(4). This increase in oxygen consumption appears to range from about 1% in some athletes to as much as 12% in others! In other words, in some triathletes it 'costs' 12% more to run at race pace after the bike portion of a triathlon than it does just to run. Small wonder that running feels tough after biking!

Significantly, this rise in oxygen cost (or decrease in economy) at the beginning of the run portion of a triathlon is inversely related to triathlon ability level: the greater the rise (compared to running without previous cycling), the poorer the performance(5). Thus, it makes sense for triathletes to train in a way that reduces this drop in economy (more on this in a moment). Interestingly enough, in this study the researchers were able to show that athletes who best preserved economy tended to be the ones who maintained normal leg stiffness from the outset of their runs - ie their legs were better controlled, more stable and with roughly the same resilience associated with usual running. To put it another way, their legs were less fatigued and better controlled by their nervous systems.

What causes the oxygen squandering which is so typical of the bike-run transition? The mechanical changes mentioned above undoubtedly play a role, and glycogen depletion may be an additional interrelated factor. If triathletes start their runs with low muscle-glycogen concentrations because of glycogen depletion during the bike phase, their leg muscles might turn increasingly to fat to supply the energy needed to continue. For a given power output (running speed), the utilisation of fat rather than carbohydrate for energy causes a significant rise in the rate of oxygen consumption. Thus, it is critically important for triathletes to maximally load their muscles with glycogen before the event - and to keep carbohydrate flowing into the body amply and steadily during the competition itself. At least five regular swallows of sports drink should be taken in every 15 minutes during the bike portion of a triathlon, and a 10oz 'slug' of sports drink should probably be taken right at the beginning of the biking. Plain water should not be ingested along with the sports drink, as this would dilute it in the stomach and lower the absorption rate of carbs. This consumption pattern should also help control rises in body temperature and limit the risk of dehydration, both of which can impair economy.

In an exploration of bike-run transition problems, which attempted to mimic an Olympic-style triathlon, five triathletes ran 10k after either a normal warm-up or a strenuous 40k cycle ride. Average running speed was significantly slower after the cycle ride and there was also a trend toward decreased stride lengths(6).

Drafting reduces physiological stress

s you might expect, running after a cycling segment in which drafting has taken place is significantly different from running after non-drafting conditions. In one study, eight elite male triathletes participated in 75k-20k-5k triathlons with and without drafting in the 20k bike portion of the event. For a given cycling speed, drafting decreased oxygen consumption, ventilation, heart rate, and blood-lactate values during the cycle portion of the event. The total reduction in energy expenditure was considerable and led to reduced physiological stress at the outset of the running portion of the race(7).
This raises a key question: do various cycling strategies have a large impact on transition running performance? Specifically, does it matter whether the cycling portion of a competition is completed with a fairly steady power output or with rather wide variations in speed? Little is known about this important subject, although one study has supported the notion that uniformity of intensity might be preferable. This study showed that when individuals either cycled steadily at 58% of peak power for 150 minutes or allowed intensity to vary widely while keeping 58% as the average power output for 150 minutes, the former strategy produced much better 20k cycle performances afterwards(8). Whether running performance would also be better if cycling intensities were held fairly constant remains unclear.

It does appear, however, that the cost of running is directly related to the intensity of the preceding cycling. In one piece of research, the cost of running was increased by 5.7% (over control running) after 10 minutes of steady-state cycling at 60% of VO2max; after 10 minutes of cycling at 80% VO2max, the cost of running went up by 8.7%(9). This implies that coming into the transition area like a rocket might be good for the time taken to complete the cycling portion (and might lead to a favourable position in the transition area and thus a quick exit into the running segment) but could also chip away at overall running performance, especially during the first kilometre or so.

Interestingly, scientific data obtained from draft-legal World Cup events has shown that drafting is associated with quite variable overall power outputs, rather than the relatively steady-state cycling one might expect. Scientists have explained that these swings in intensity are associated with attempts to bridge gaps, maintain contact with a pack and contribute to the overall speed of the lead or chasing packs. Indeed, for one competitor cycling velocity averaged 40k per hour but ranged from 24-56 k/hour during the event(10). As above, it is unclear how these wide swings in intensity influence the running portion of the triathlon, although one might argue that excessive 'swinging' could deplete glycogen more rapidly. In addition, a dramatic upward swing at the end of the bike stage is nearly certain to make the running harsher in nature.

Exercise scientists have analysed runners' biomechanics during the run portion of the bike-run transition to determine whether running form actually changes in comparison with routine running and whether conscious attempts to control form might improve economy and performance. Several (but not all) of these studies have shown that stride length and frequency don't change much when running after cycling(11). The research has also detected very few changes in hip or ankle vertical oscillation, thigh, knee, and trunk angle during the stance phase of the gait cycle, and 'flight time' - the time between toe-off on one foot and initial ground contact with the other(12).

Runners use 'death-march' style after quitting their bikes

Perhaps the only consistent difference in running form during the bike-run transition (compared with regular running) is that athletes tend to run with a more 'stooped' posture - ie with their upper bodies inclined forwards(13). This 'death-march' style may be a sign of delayed adjustment from the forward-leaning style of cycling; alternatively it could reflect fatigue. However you explain it, the forward slump probably produces a dip in economy and may be responsible, at least in part, for the 1-12% drop in running efficiency commonly observed during the bike-run transition. The solutions to this problem would, of course, be to:

a. improve low-back strength in a functional way to prevent this upper-body droopiness;
b. practise the bike-run transition often, concentrating on preserving good posture at the start of the run;
c. enhance overall fitness to lessen fatigue at the transition stage.

As mentioned above, the loss in economy during transition may be partly related to neural factors - an inability of the nervous system to adjust quickly to the new pattern of mobility and recruit motor units in an optimal fashion. Evidence for this theory comes from the loss of coordination commonly experienced by novice triathletes during the run stage of the bike-run transition. A very interesting study, which also supports the importance of 'neural factors', showed that adaptation to neurosensory feedback from prolonged running or stationary biking persists in triathletes after the cessation of each of these activities(14). In the words of Millet, mentioned above, '...postural compensation at the start of the cycle-to-run transition may be out of phase with actual neurosensory feedback'.

The best solution to this problem would be to practise the bike-run transition repeatedly during training to force the nervous system to learn to adapt quickly to the changes in body position and overall mechanics of movement associated with transition. For this purpose, I recommend the 'pile-of-bricks' training session, in which triathletes (or duathletes) warm up thoroughly and then alternate 10-15 minute intervals on the bike at race-type intensity with 10-15 minute running intervals, also at triathlon intensity. Initially, a triathlete might use just three 10-minute intervals of biking and running per workout, followed by a gradual progression to four or five 15-minute intervals of each activity. During each transition within the session, triathletes should focus on maintaining normal posture, form, stride rate and stride frequency while running.

Working out blindfold might help

To improve running economy during transition, some experts favour the 'blind transition workout', in which cycling blindfold on a stationary bike is alternated with running blindfold on a treadmill (or in an obstacle-free field) at race-type intensities. The idea is to develop sensitivity to physical and sensory information by taking visual input out of the picture. Such sessions are probably helpful, but should be approached with caution: always work with a partner to avoid falls on the treadmill, for example.

As you attempt such workouts, bear in mind that the combined cycle and run time for a triathlon competition is best predicted by two key factors: physiological variables associated with cycling power and the extent of change in running economy during the bike-run transition(15). Workouts like the pile-of-bricks session will work on the latter factor but, strangely enough, many triathletes fail to include back-to-back cycle-run training in their overall programmes. Five-time world champion Simon Lessing doesn't do it, and an informal poll has revealed that 27 out of 30 members of the British national team also fail to include such workouts in their programmes.

What about cycling power?

The inclusion of power as a potent predictor of performance indicates that training sessions which feature maximal-intensity 1-2 minute work intervals, followed by 2-4 minute recoveries and also five-minute work intervals at around 90% of maximal effort, with 3-5 minute recoveries, may be more important to triathletes than the standard fare of 3-5 hour rides at more modest power outputs. However, if you are going to be competing in super-Olympic distance triathlons, you do need sessions that feature 2-4 hour cycle workouts followed by 90-180 minutes of running. These efforts build stamina and mental fortitude, have a modest impact on overall fitness and will help you get accustomed to running with low muscle-glycogen levels. Here, then, are my final take-home messages on triathlon training and, particularly, the bike-run transition:

1. Practise the transition repeatedly during training, making sure your running mechanics are not disturbed by the change from cycling to running. This will help minimise your time in the transition area and will also improve your running economy during the critical first kilometre of the run stage.
2. Draft during the cycling portion of your triathlon. This will help both your cycling performance and your running performance during the transition.
3. Load your muscles with glycogen adequately before the race and use sports drinks appropriately (as indicated above) throughout the cycling and running segments of the competition.
4. If possible, avoid racing hell-for-leather into the transition area. This strategy might shave some seconds off your cycling time and a few more off your transition-area passage (if you manage to arrive a few seconds ahead of competitors), but it will further complicate the initial portion of the run phase, adding muscle fatigue and potential downturns in muscle pH to the unavoidable transition problems of 'neural catch-up' and blood redistribution.
5. Look on the first kilometre of the run portion of a triathlon as your opportunity to outdistance rivals. If you follow the strategies outlined in this article, you will be much better prepared than your competitors to handle the stresses of the bike-run transition and therefore able to outperform them during the early phases of the running stage. If you can put some distance between yourself and your competitors while they are really struggling, you can beat them, even if they are slightly better than you in running-only road races.
6. Even if you are a middle to long-distance triathlete, don't hesitate to utilise triple-supersprint triathlons as training sessions. These back-to-back 3k, 7k and 2k triathlons are great for overall fitness, power, and the ability to shift easily from cycling to running without a drop-off in economy and speed.
7. Use 'fatigue drills' to improve your ability to run well even when your leg muscles are fatigued from cycling. Cycle uphill or in a high gear (or against heavy resistance on a stationary cycle) for 3-5 minutes to induce significant leg-muscle fatigue, then jump off the bike and run at 5k pace for four minutes-or-so, then repeat the pattern. Start with two intervals and work up to four to five over time.

Owen Anderson

References

1. Annals of Sports Medicine, vol 3, pp 220-225, 1988

2. Actes du Premier Symposium International de L'Entrainement en Triathlon, Les Cahiers de l'INSEP, vol 20, pp 143-145, 1997

3. British Journal of Sports Medicine, vol 34, pp 384-390, 2000

4. WSPAJ, vol 3, pp 29-39, 1995

5. International Journal of Sports Medicine, vol. 21, pp 1-6, 2000

6. Proceedings of the XIth Symposium of the International Society of Biomechanics in Sport, Amherst, MA, USA, pp 86-88, 1993

7. Medicine and Science in Sports and Exercise, vol 31, pp 599-604, 1999

8. Medicine and Science in Sports and Exercise, vol. 29, pp 684-687, 1997

9. Annals of Sports Medicine, vol. 3, pp 25-29, 1986

10. 2nd INSEP International Triathlon Congress, Les Cahiers de l'INSEP, vol 24, pp 224-232, 1999

11. European Journal of Applied Physiology, vol 77, pp 98-105, 1998

12. Journal of Applied Biomechanics, vol 12, pp 470-479, 1996

13. International Journal of Sports Medicine, vol 18, pp 330-339, 1997

14. European Journal of Applied Physiology, vol. 76, pp. 55-61, 1997

15. Medicine and Science in Sports and Exercise, vol 29-5 (supplement), p S221 (abstract 1262), 1997