Sport & Performance
Concurrent training: does endurance work blunt strength gains, and how to schedule both
Concurrent training means developing strength and endurance in the same programme, either within one session or on separate days. The worry attached to it is the interference effect: the idea that endurance training reduces the gains a person would make from strength training alone. Current evidence gives a narrower answer than gym folklore suggests. For most healthy adults, adding endurance work does not measurably reduce gains in maximal strength or muscle size. Explosive strength is the exception, and the clearest ways to protect it are to separate the two kinds of training by several hours or, when they share a session, to lift first.
What interference would affect
Strength training produces several different adaptations, and the research measures them separately:
- Maximal strength is the heaviest load a person can move, usually tested as a one-repetition maximum (1RM).
- Explosive strength is the ability to produce force quickly, tested with jumps, throws or the rate at which force rises during a contraction.
- Hypertrophy is growth in muscle size, measured for a whole muscle or for individual muscle fibres.
Interference does not have to affect all three equally, and the studies below show that each responds differently.
Two explanations are usually offered for why it happens at all. The first is fatigue: an endurance session leaves the legs tired, so the following strength session is lifted with less load, less speed or fewer repetitions, and the training stimulus shrinks. The second is cellular: endurance and strength training trigger different signals inside muscle, and the endurance signals might partly dampen those that drive growth. The cellular explanation has been difficult to confirm consistently in human studies and is best treated as a hypothesis. The fatigue explanation matters more in practice because it depends on things a coach controls, namely the order of sessions and the time between them.
What the meta-analyses show
A 2022 meta-analysis by Schumann and colleagues pooled 43 studies in healthy adults. Each compared a strength programme lasting at least four weeks with the same programme plus aerobic training. The results are reported as a standardised mean difference (SMD), which expresses the gap between groups in units of their spread; values around 0.2 are conventionally called small and around 0.5 moderate.
| Outcome | Concurrent vs strength only (SMD) | Interpretation |
|---|---|---|
| Maximal strength | −0.06 | No meaningful difference |
| Muscle hypertrophy | −0.01 | No meaningful difference |
| Explosive strength | −0.28 | Small, statistically clear reduction |
The reduction in explosive strength was larger when both kinds of training were done in the same session. When sessions were separated by at least three hours, the difference was no longer statistically significant. The type of aerobic training, weekly frequency, training status and age did not change these results. One limit matters here: the training-status comparison was between untrained and physically active people, so the findings say little about highly trained athletes carrying large endurance volumes.
A companion 2022 meta-analysis of muscle-fibre size by Lundberg and colleagues, based on 15 studies, found a small negative effect of concurrent training on fibre growth that did not reach statistical significance overall. In a subgroup analysis, running was associated with less growth of type I fibres, the slow-twitch fibres used heavily in endurance work, while cycling was not. The authors describe this as preliminary.
An older 2012 meta-analysis by Wilson and colleagues, covering 21 studies, also found that running but not cycling reduced hypertrophy and strength gains, and that longer and more frequent endurance sessions were associated with smaller gains in strength, power and size. The newer, larger analysis did not confirm the running–cycling difference for whole-muscle outcomes, so the modality question remains open. Both point the same way on one practical matter: the more endurance volume is added, the more care the schedule needs.
Session order within one workout
When strength and endurance share a session, order can matter. A 2018 meta-analysis by Eddens, van Someren and Howatson pooled 10 studies of healthy adults training for at least five weeks. Lifting before endurance work produced lower-body dynamic strength gains about 6.9 percentage points larger than the reverse order (95% confidence interval 2.0 to 11.9). Order made no detectable difference to muscle hypertrophy, static strength, aerobic capacity or body fat. Lifting first therefore benefits leg strength and, on this evidence, costs nothing aerobically.
Recovery time between sessions
A randomised study by Robineau and colleagues tested the gap directly. It assigned 58 amateur rugby players to seven weeks of two strength and two aerobic sessions per week, always lifting first, with 0, 6 or 24 hours between the two. The 0-hour group gained less bench-press and half-squat strength than the 6-hour, 24-hour and strength-only groups. Aerobic capacity improved most in the 24-hour group.
This is a single, short study in young male team-sport players, analysed with a statistical method that some researchers dispute, so the exact thresholds should not be taken as precise. It does agree with the meta-analytic finding that separating sessions by at least three hours protects explosive strength.
A worked weekly example
The table is an illustration for a hybrid athlete who wants to keep strength while building race fitness. It is not a prescription; the right split depends on the athlete's goal, history and recovery.
| Day | Session | Scheduling logic |
|---|---|---|
| Monday | Lower-body strength in the morning, easy cycling in the evening | Two sessions separated by more than 6 hours |
| Tuesday | Running intervals | No heavy leg work on the same day |
| Wednesday | Upper-body strength, then an easy run | Shared session, lifting first |
| Thursday | Rest or easy aerobic work | Recovery before the next leg session |
| Friday | Lower-body strength with jumps | Explosive work kept away from endurance sessions |
| Saturday | Long easy run or race simulation | Race-specific work with a full day before the next lift |
| Sunday | Rest |
Keeping hard running away from the day before a heavy leg session follows from the fatigue explanation rather than from a study that tested it directly.
In a group class that combines a strength block with a conditioning block, the same logic applies: on days when leg strength is the goal, the strength block goes first. On race-practice days the order follows the race instead. The live heart-rate board shows the cardiovascular load of the conditioning block, but it does not show how fatigued the leg muscles are for lifting, so the plan for the strength block should come from the programme rather than the colours.
Key points
- Expect little or no loss of maximal strength or muscle size when moderate endurance training is added to a strength programme.
- Separate explosive work from endurance sessions by at least three hours, and longer when the schedule allows.
- Lift first when both share a session and lower-body strength is the priority.
- Add endurance volume gradually and watch whether strength numbers keep rising, because larger volumes are linked to larger costs.
- Treat the running-versus-cycling question as unsettled, and consider cycling for extra aerobic work when muscle growth is the main goal.
Sources
- Schumann M et al. Compatibility of concurrent aerobic and strength training for skeletal muscle size and function: an updated systematic review and meta-analysis. Sports Medicine, 2022.
- Lundberg TR et al. The effects of concurrent aerobic and strength training on muscle fiber hypertrophy: a systematic review and meta-analysis. Sports Medicine, 2022.
- Wilson JM et al. Concurrent training: a meta-analysis examining interference of aerobic and resistance exercises. Journal of Strength and Conditioning Research, 2012.
- Eddens L, van Someren K, Howatson G. The role of intra-session exercise sequence in the interference effect: a systematic review with meta-analysis. Sports Medicine, 2018.
- Robineau J et al. Specific training effects of concurrent aerobic and strength exercises depend on recovery duration. Journal of Strength and Conditioning Research, 2016.
Heart rate is a training signal, not medical advice. This article describes general training principles rather than an individual programme.