endurance | resistance

Endurance and resistance training: New findings on the 'interference effect'

The specificity of training principle states that the nature of adaptation is dependent on the type of training practised. It therefore follows that combining two types of training – such as resistance and endurance training – is likely to interfere with the training response induced by either type of training alone.

A study published in 1980 first provided evidence for the existence of an ‘interference effect’ between resistance and endurance training by demonstrating that strength gains were hindered when the two types of training were performed concurrently. But subsequent research has been inconclusive, partly because of variations in research methodologies, but also because of variations in training volume.

Faced with a wealth of contradictory results, a Texas-based research team set out to derive clear answers from a study comparing the effects of endurance training, resistance training and concurrent training (the latter matching the individual components of resistance and endurance training for volume) in hitherto untrained male volunteers. They expected to support the initial hypothesis that gains in muscle strength/power and aerobic capacity would be less after concurrent training than after resistance or endurance training alone respectively.

Forty-five untrained men were randomly assigned to one of three groups, each undertaking a 12-week training programme, as follows:

  • Resistance training (RT), completing a series of standard resistance training exercises twice weekly and thrice weekly on alternate weeks. Individualised daily workouts of three sets of 6-10 repetitions on eight exercises were designed to train all the major muscle groups of the body. The intensity and number of reps for each exercise were progressively increased every two weeks;
  • Endurance training (ET), running on an indoor treadmill or outdoor running surface 2-3 times a week (as above) for 20-40 minutes at intensities determined by percentage of heart rate reserve. As for RT, the intensity and/or duration of each session were increased bi-weekly as training progressed;
  • Concurrent training (CT), performing the RT programme three times and the ET programme twice on every odd-numbered week and vice versa on alternate weeks. In this way, subjects completed the same number of endurance and resistance workouts over the course of the study as the ET and RT subjects respectively.

All subjects were measured before and after the training period for: weight; percentage body fat; peak oxygen consumption (V02max); isokinetic peak torque and average power produced during single-leg flexion and extension at 60 and 180°; one-repetition maximum leg press and bench press; vertical jump height and calculated jump power.

Contrary to the researchers’ hypothesis, subjects in the RT and CT groups made similar gains in maximum leg-press and bench-press strength, both of which were significantly greater than those of subjects in the ET group. Weight and lean body mass increased significantly in the RT and CT groups, while percentage body fat was significantly decreased in the ET and CT groups. V02max was significantly improved only in the ET group; peak torque during flexion and extension at 180° increased in the RT group; jump power improved significantly only in the RT group; and no group showed a significant change in vertical jump height.

‘Our findings,’ conclude the researchers, ‘do not support the existence of an “interference phenomenon” between concurrent resistance and endurance training with respect to strength gains…The effects of concurrent training on the development of muscle power are less clear, but our findings suggest that when resistance training is performed singularly, it is superior to concurrent training when the goal is to improve muscle power.

‘Finally, our data show that concurrent resistance and endurance training may interfere with the improvements in aerobic capacity that can be expected when healthy young men engage in an equal volume of endurance training alone.

‘These findings have important implications for professionals designing exercise programmes to improve health and fitness in the general population.’

Med Sci Sports Exerc, vol 36, no 12, pp2119- 2127, 2004

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