Can't Run? Aqua Jogging, the Elliptical and What Keeps Run Fitness When Injured

Injuries are a normal part of running, and triathletes are no exception. A stress reaction in a shin, a calf strain or a flare of Achilles pain can stop your running for weeks while your swimming and cycling carry on.

Triathletes have one advantage here: two other sports to keep training. But neither swimming nor cycling is running. This article covers what keeps run-specific fitness during a break, what the evidence says about aqua jogging, the elliptical and the bike, and why fitness isn't the only thing that matters when you return.

What you lose when you stop running

TriForward's "The Off-Season: How Much Time Off Before Fitness Really Slips" covers detraining in detail. In short, aerobic fitness starts to decline within a couple of weeks of stopping training, with falls in blood volume and VO2max. For a triathlete who keeps swimming and cycling, the aerobic losses will be much smaller than for someone who stops all training.

What a swim-bike triathlete is likely to lose, by inference rather than from a single study, is the running-specific part:

• Running economy, which depends on movement skill and how muscles and tendons store and return energy.
• Muscle and tendon tolerance to impact, which takes weeks to months to build.
• Running-specific muscle endurance, particularly in the calves and quads.

Cross-training can help with some of these more than others.

Deep-water running: what it is

Deep-water running, often called aqua jogging, means running in the deep end of a pool without touching the bottom, usually wearing a flotation belt. The movement mimics running, with an upright trunk, a slight forward lean and a running arm action. There's no impact, because your feet never land.

A 2003 review by Reilly, Dowzer and Cable in the Journal of Sports Sciences summarised the physiology:

• Maximal oxygen uptake and heart rate are lower in water than during running on land.
• At submaximal intensities, blood lactate is higher than on a treadmill at the same oxygen uptake.
• Spinal loading is reduced, supporting its use for injury prevention.
• Training studies confirm it works, with the clearest gains seen in water-based tests.
• Trained endurance athletes maintain aerobic performance for up to 6 weeks with deep-water running.

The 6-week trial

A 1996 study by Randall Wilber and colleagues in Medicine & Science in Sports & Exercise compared treadmill running with deep-water running in 16 trained male runners, with an average VO2max of 58.6 ml/kg/min.

• Runners were split into two groups matched for VO2max. One trained on a treadmill and one in deep water, for 6 weeks.
• Both groups trained 5 days a week, alternating 30 minutes at 90 to 100% of VO2max with 60 minutes at 70 to 75% of VO2max.

The results:

• VO2max didn't differ within or between groups: 58.4 to 60.1 ml/kg/min in the treadmill group and 58.7 to 59.6 in the water group.
• Ventilatory threshold and running economy didn't change in either group.
• Blood markers and body composition didn't differ between groups.

The authors concluded that deep-water running may serve as an effective alternative to land-based running. Note that this was a demanding programme, with hard sessions on alternate days. The runners weren't injured, and all were men.

The 4-week trial

A 1997 study by Bushman and colleagues, also in Medicine & Science in Sports & Exercise, asked a more practical question: what happens to performance when deep-water running replaces all running? It involved 11 well-trained competitive runners, 10 men and 1 woman, aged around 32.

• For 4 weeks, they did only deep-water running, 5 to 6 days a week, for 20 to 24 sessions in total. They practised the technique beforehand.
• Before and after, they did a 5-km treadmill race, a submaximal economy test and a VO2max and lactate threshold test.

The results:

• 5-km time didn't change significantly: 1,142.7 seconds before and 1,149.8 seconds after. Inference: that's roughly 19:03 and 19:10, a difference of about 7 seconds, or 0.6%.
• VO2max (63.4 vs 62.2 ml/kg/min), lactate threshold velocity and economy didn't change significantly.

The authors concluded that competitive runners maintained treadmill running performance for 4 weeks when deep-water running replaced land training. There was no control group, so we can't say how much fitness the runners would have lost without it.

Why heart rate misleads in the pool

A 1999 study by Dowzer and colleagues in Ergonomics tested 15 trained male runners in three maximal tests: treadmill running, shallow-water running and deep-water running with a buoyancy vest.

• Peak oxygen uptake in deep water was 75.3% of the treadmill value, and 83.7% in shallow water.
• Peak heart rate in deep water was 87.2% of the treadmill value, and 94.1% in shallow water.

The authors still concluded that water provides an adequate training stimulus. Inference: if your land-based heart-rate zones put threshold at 165 beats per minute, you may never reach 165 in the pool even when working very hard. Use perceived effort and cadence alongside heart rate, and set lower targets in the water.

The elliptical

The elliptical trainer mimics a running motion without the impact of landing, and it's widely available. The research is thin.

The only training study found for this article was a 2011 study by Joubert and colleagues in the International Journal of Exercise Science. It involved 20 recently trained adults, 12 women and 8 men, aged around 24.

• All participants ran 4 days a week for 4 weeks to build fitness.
• They were then split into three groups for 3 weeks: continued running, elliptical training at the same prescription, or no training.

The results:

• VO2max fell slightly in all groups, by 0.8% with running, 1.5% with the elliptical and 4.8% with no training. None of these changes was statistically significant.
• Time on the treadmill test fell significantly only in the no-training group.

This study was very short, in people who had only just started training, and its VO2max values were estimated rather than measured directly. It hints that the elliptical can hold fitness for a few weeks, but it can't tell a trained triathlete much.

Cycling

For triathletes, cycling is the obvious fallback, since you're already doing it. A 1994 review by Hirofumi Tanaka in Sports Medicine looked at how training effects on VO2max transfer between cycling, running and swimming. Key points:

• Some transfer of training effects on VO2max exists from one mode to another.
• Swimming produces minimal transfer.
• Cross-training effects never exceed those of sport-specific training.
• Specificity matters more for highly trained athletes.
• Cross-training may be a useful supplement during injury rehabilitation.

Inference: for a triathlete who already rides several times a week, extra cycling will help maintain the aerobic engine, but it's unlikely to preserve running-specific economy and muscle endurance as well as a movement that looks like running. That's one reason deep-water running may be more useful than a few extra bike hours.

Who was studied

Before applying these findings, it's worth being clear about who took part:

• Almost all were men. Wilber's and Dowzer's runners were all male, and Bushman's group included one woman. Only the short elliptical study had more women than men.
• They were healthy, not injured. The trials asked whether water running could replace land running in fit runners, not whether it helps people recover from an injury.
• They were runners, not triathletes. None of the participants was also swimming and cycling, so we don't know how deep-water running adds to a full triathlon week.
• The samples were small, between 11 and 20 people.
• The trials are old. The main deep-water running studies date from the 1990s, and there's been little new training research since.

Inference: the direction of the evidence is consistent, and it's plausible that it applies to injured triathletes. But it's an extrapolation, which is why the principle behind this article is graded as limited.

Fitting cross-training into a triathlon week

A triathlete who can't run still has a full week to manage. Some practical points, which are inference rather than tested advice:

• Don't simply add the lost run hours to the bike. Extra cycling adds fatigue and may aggravate some injuries, and it doesn't replace the running movement.
• Swap like for like where you can. Replace an interval run with a deep-water interval session, and an easy run with an easy one.
• Watch total fatigue. Deep-water running is harder than it looks, especially the first few sessions. Hard pool sessions on top of hard bike sessions can leave you more tired than your normal week.
• Use the time. An injury break is a chance to work on swim technique or strength training that's normally squeezed out, if your clinician agrees.
• Keep pool sessions back to back where practical. Many triathletes do a deep-water session straight after a swim, which saves travel time.

Choosing your cross-training

The choice depends on your injury and what your clinician allows. A rough guide, based on how much each one resembles running and how much it loads injured tissue:

• Deep-water running: no impact, running-like movement, best evidence for maintaining run fitness. Often suitable for bone stress injuries once a clinician agrees.
• Elliptical: running-like, low impact, but loads the legs through the feet. Little evidence in trained runners.
• Cycling: maintains aerobic fitness, already familiar to triathletes, but not running-specific. Can aggravate some knee, hip and Achilles problems.
• Swimming: keeps you training but has little transfer to running.

How to aqua jog well

These are practical suggestions based on the trials and common practice, not tested protocols:

1. Use a flotation belt and stay in water deep enough that your feet don't touch the bottom.
2. Copy your running form: upright trunk, slight forward lean, running arm swing, and a leg action that pushes down and back. Avoid a cycling or treading-water motion.
3. Go by effort, not pace. You'll move slowly, and that's fine.
4. Mirror your normal week. The Wilber trial used hard 30-minute sessions alternating with steady 60-minute sessions. Intervals of 1 to 5 minutes with short rests help with boredom and intensity.
5. Keep sessions roughly as long as your runs, but build up, because the movement is new and tiring.

Returning to running

Holding fitness doesn't mean your body is ready to run. Bone, tendon and muscle lose their tolerance to impact during time off, and the injured tissue may still be healing. The trials above measured fitness, not readiness for impact.

Inference: athletes who keep their aerobic fitness through cross-training may feel able to run far more than their legs can tolerate. Follow your clinician's return-to-run plan, start with short run-walk sessions, and increase gradually. TriForward's "Forget the 10% Weekly Rule" and "Calf and Achilles Capacity" cover load progression and tendon loading.

A triathlon scenario

The following example is illustrative, not drawn from a study. A 36-year-old age-grouper is diagnosed with a low-risk tibial bone stress injury 12 weeks before a 70.3. Their sports doctor advises no running for about 6 weeks.

Based on the evidence above, with their clinician's agreement, they might:

• Replace each run with a deep-water session of similar duration, including one interval session a week.
• Keep swimming and cycling as normal, if pain-free.
• Use perceived effort in the pool rather than run heart-rate zones.
• Return to running with a gradual run-walk plan once cleared, accepting that the race goal may need to change.

Common mistakes

• Running through pain. Cross-training is only useful if you stop running in time.
• Treading water instead of running. Poor form reduces the running-specific benefit.
• Chasing land heart-rate zones in the pool. You may never reach them.
• Choosing cross-training that aggravates the injury. Ask your clinician.
• Returning to full running volume because you feel fit. Fitness returns faster than tissue tolerance.
• Ignoring why you got injured. Training load, fuelling and recovery all play a part. TriForward's "Under-Fuelled, Not Undertrained" covers energy availability.

What we don't know

• Whether deep-water running maintains performance beyond 6 weeks, or in injured athletes rather than healthy ones.
• How it compares with the elliptical or cycling in trained runners or triathletes.
• The effect in women and masters athletes, who were barely represented in these trials.
• Whether maintaining fitness reduces re-injury risk when running resumes.
• The best mix of intensities in the water. The trials used either a demanding interval-and-steady programme or the runners' usual training transferred to the pool, and none compared them.
• Whether deep-water running helps running off the bike. No study has looked at brick or race performance after a cross-training block.
• How shallow-water running compares for maintaining run fitness. It reaches higher heart rates than deep water but adds some impact, and its training effects in trained runners are largely untested.

References

• Wilber RL, Moffatt RJ, Scott BE, Lee DT, Cucuzzo NA. Influence of water run training on the maintenance of aerobic performance. Medicine & Science in Sports & Exercise, 1996;28(8):1056–1062. doi:10.1097/00005768-199608000-00017
• Bushman BA, Flynn MG, Andres FF, Lambert CP, Taylor MS, Braun WA. Effect of 4 wk of deep water run training on running performance. Medicine & Science in Sports & Exercise, 1997;29(5):694–699. doi:10.1097/00005768-199705000-00017
• Reilly T, Dowzer CN, Cable NT. The physiology of deep-water running. Journal of Sports Sciences, 2003;21(12):959–972. doi:10.1080/02640410310001641368
• Dowzer CN, Reilly T, Cable NT, Nevill A. Maximal physiological responses to deep and shallow water running. Ergonomics, 1999;42(2):275–281. doi:10.1080/001401399185649
• Joubert D, Oden G, Estes B. The effects of elliptical cross training on VO2max in recently trained runners. International Journal of Exercise Science, 2011;4(1):4–12. doi:10.70252/XTLO7148
• Tanaka H. Effects of cross-training: transfer of training effects on VO2max between cycling, running and swimming. Sports Medicine, 1994;18(5):330–339. doi:10.2165/00007256-199418050-00005