Strength and isokinetic testing for runners: fewer injuries, better running economy

The runner who wants to run faster almost always does the same thing: runs more. Aerobic training remains the core — no amount of lifting replaces it. Yet the data of recent decades point to something many runners leave unused: strength training does not compete with endurance, it supports it — and it is at the same time the best-documented injury-prevention measure we have.

First, the obvious: the aerobic base is not negotiable

Distance performance is determined by three classic pillars: maximal oxygen uptake (VO₂max), the thresholds at which you can sustain it, and running economy — how much oxygen you spend to run at a given speed. The first two are built with mileage, structured zones and patience; nothing changes there. Strength training is not added to “steal” time from that work — it is added to answer the third pillar, economy, and to keep the runner healthy enough to get the work done.

This distinction matters, because it also explains why there is no conflict: in studies of concurrent training, VO₂max, velocity at VO₂max and lactate are not adversely affected by the addition of strength work. Nor does body mass increase — a fear that keeps many runners away from the gym and that the literature does not confirm.

What performance gains: 2–8% in running economy

The most complete systematic review in the field (Blagrove, Howatson & Hayes, 2018 — 24 studies in middle- and long-distance runners) found that adding strength training improves running economy by 2–8% compared with a control group that only ran, alongside improvements in 1.5–10 km time trials and in anaerobic speed qualities. The authors’ recommendation is practical: two to three sessions per week, with a variety of methods (heavy resistance, explosive resistance, plyometrics).

To grasp the size of that: a 4% improvement in economy means that at the same speed you spend appreciably less oxygen — that is, at the same physiological cost, you run faster. It is an improvement you will hardly achieve by simply adding mileage to an already well-trained runner.

The mechanisms, as summarised by Rønnestad & Mujika (2014), are no mystery: better neuromuscular efficiency, increased musculotendinous stiffness (the tendon acts as a better spring and returns more elastic energy with every stride), delayed recruitment of the less economical type II fibres, and conversion of IIX fibres into more fatigue-resistant IIA.

And now the strongest finding: injuries

Here the literature is unusually clear. The meta-analysis by Lauersen and colleagues (2014, British Journal of Sports Medicine) across 25 randomised trials with 26,610 participants showed that strength training reduced sports injuries to less than one third (RR 0.32), while overuse injuries — the runner’s category par excellence — were almost halved. In the same analysis, stretching showed no protective effect at all (RR 0.96).

The updated review from the same group (Lauersen et al., 2018) confirmed the magnitude (RR 0.34) and added something practically useful: the effect is dose-dependent — every 10% increase in strength-training volume was associated with a reduction in injury risk of more than four percentage points. So this is not a matter of “do something just to say you do”; volume and intensity count.

Where isokinetic testing comes in

If strength is the medicine, isokinetic testing is the diagnosis. On the isokinetic dynamometer (Cybex) the joint moves at a constant angular velocity: the harder you push, the more resistance you meet. That is how we objectively measure the torque of each muscle group across the whole range of motion, the H:Q ratio (hamstrings to quadriceps) and right–left asymmetries — three things running on its own will never reveal to you.

In runners this comes with a particularity worth stressing. In healthy, well-trained long-distance runners (Dellagrana et al., 2015), peak torque and total work were symmetrical between the two legs at low angular velocities — but at high velocities (240°/s) a 13% asymmetry appeared in the power of the knee flexors, against only 2% at 60°/s. In other words: the imbalance is there, but it hides — it shows up only when the measurement is made at speeds that resemble running. A “passed the test” on a slow protocol means nothing for a runner.

The second classic example concerns the hip. Fredericson and colleagues (2000) measured runners with iliotibial band syndrome (ITBS) and found significantly weaker abductors on the affected leg — both relative to their own healthy leg and relative to healthy runners. After a six-week strengthening programme emphasising the gluteus medius, abduction torque increased by 35–51% and 22 of the 24 athletes returned to pain-free running, with no recurrence at six months. The pain was at the knee; the cause was at the hip. Without measurement, that is guesswork.

How strength fits into a runner’s week

• 2–3 sessions per week, lasting 30–45 minutes — that is enough. No bodybuilding programme is needed.
• Heavy resistance with few repetitions (high load, 3–6 repetitions, under control and with sound technique) — it is this form, not many repetitions with light weight, that drives the neuromuscular adaptations which improve economy.
• Plyometrics (jumps, bounds) for the elasticity of the musculotendinous system — in small doses and progressively.
• Placement: ideally on a separate day or after an easy run, never before a quality session. Keep ≥6 hours away from the hard aerobic session wherever possible.
• Targeted: hamstrings, glutes (especially the abductors), calves/Achilles and trunk — wherever the measurement shows a deficit, not whatever comes to hand.
• During tapering: volume is reduced, intensity is maintained — strength is not abandoned in the weeks before the race.

What we recommend at the lab

For the runner, the full picture emerges from combining two measurements that answer different questions:

• Cardiopulmonary exercise testing (CPET) — VO₂max, thresholds and personal Z1–Z5 zones: how big the engine is and where it works properly.
• Isokinetic testing (Cybex) — torque, H:Q and asymmetries, on a protocol with high angular velocity: where the weak point that will stop you is.

Both are recorded in your account at results.ergometrictests.com, with comparison against norms and tracking from test to test — so that the next assessment shows whether the work in the gym paid off. See also the related articles on VO₂max and training zones and on isokinetic testing.

The conclusion

Aerobic training remains the heart of a runner’s preparation — and nothing in this article says otherwise. What the literature says is that strength is its multiplier: it makes every kilometre more economical and drastically reduces the chance of losing weeks of training to an overuse injury. And it is measurement that shows exactly where the strength work has to go, instead of guessing.

References

• Blagrove RC, Howatson G, Hayes PR (2018). Effects of Strength Training on the Physiological Determinants of Middle- and Long-Distance Running Performance: A Systematic Review. Sports Medicine 48(5):1117–1149. doi:10.1007/s40279-017-0835-7
• Rønnestad BR, Mujika I (2014). Optimizing strength training for running and cycling endurance performance: A review. Scandinavian Journal of Medicine & Science in Sports 24(4):603–612. doi:10.1111/sms.12104
• Lauersen JB, Bertelsen DM, Andersen LB (2014). The effectiveness of exercise interventions to prevent sports injuries: a systematic review and meta-analysis of randomised controlled trials. British Journal of Sports Medicine 48(11):871–877. doi:10.1136/bjsports-2013-092538
• Lauersen JB, Andersen TE, Andersen LB (2018). Strength training as superior, dose-dependent and safe prevention of acute and overuse sports injuries: a systematic review, qualitative analysis and meta-analysis. British Journal of Sports Medicine 52(24):1557–1563. doi:10.1136/bjsports-2018-099078
• Dellagrana RA, Diefenthaeler F, Carpes FP, Hernandez SG, de Campos W (2015). Evidence for isokinetic knee torque asymmetries in male long distance-trained runners. International Journal of Sports Physical Therapy 10(4):514–519.
• Fredericson M, Cookingham CL, Chaudhari AM, Dowdell BC, Oestreicher N, Sahrmann SA (2000). Hip abductor weakness in distance runners with iliotibial band syndrome. Clinical Journal of Sport Medicine 10(3):169–175. doi:10.1097/00042752-200007000-00004

Source of bibliographic references: PubMed. This article is informational in character and does not replace medical or physiotherapy advice.