In most studies the subjects training for strength and endurance performed greater volumes of work than either the strength or endurance only groups. The compromise in strength found by most of the previous studies has been hypothesised by several authors to be due to overtraining. When results of VO2max tests for strength and endurance and endurance only groups were compared, most studies found no significant differences (3, 5, 1, 11), though many also noted that the endurance gains in combination groups were similarly, slightly lower than those of endurance only groups. It has been suggested that if compromises were due to overtraining, that this effect selectively targeted only the adaptations associated with strength(4). It appears that overtraining is not likely the cause of the incompatibility, as it has been pointed out (4) that similar results were obtained with differing total training volumes. One of the studies found, instead of a compromise, that for well trained endurance athletes strength training actually improved their performance (6). This may suggest that interference is limited if strength training is performed only when endurance has been trained to high levels. This may only be of use to athletes who need to attain a high level of endurance for their sport. One of the interference characteristics of the combined training is a lack of muscle hypertrophy (1, 11, 2, 3, 4). As previously explained this is a training response typically associated with improvements in endurance. The adaptations to strength, and endurance training show different neural responses in terms of muscle fibre recruitment. It appears that concurrent strength and endurance training may hinder the organisation of efficient motor unit recruitment patterns necessary for forceful muscular contractions at the level of the peripheral or central nervous system (2). The hypertrophy of certain muscle fibres is likely to be limited by the lack of neural stimulation which is associated with the training of strength only. One of the more recent studies (11) compared the fibre types across the different groups and found that in the E and UC groups there was an increase in type IIc muscle fibres which was not found in the C group. It was concluded that this may point to a possible incompatibility for optimising endurance mechanisms when training for both strength and endurance. Several of the studies showed compromises in strength (5, 11, 3), though it is not exactly clear what the mechanism(s) are which cause the compromises. From the studies reviewed, the impact of combined training appears to be more detrimental to potential strength and power gains and not to VO2max.