Not to beat the dead horse, but...
"I think some might find this study (review) somewhat surprising (as I did) but I thought I would post a review (as I did in another site) suggesting that at least with respect to early SIZE gains, isolation movements may be more productive than compound movements. You will note this counters the one study mentioned previously in a previous post that argued that there were no benefits with the addition of isolation movements. In one fairly recent paper (Chilibeck, 1998) the authors compared the effects of isolation (single-joint) versus compound (multiple-joint) movements with respect to stimulating muscle SIZE gains. Note the authors were interested in hypertrophy adaptations not strength adaptations. While their study was arguably confounded their review of the literature suggested that:
1. Early and greater size gains with isolation movements:
"A review of training studies using either simple single-joint or complex multi-joint exercises, outlined below, supports our finding that muscle hypertrophy occurs earlier when simpler exercises are performed. In females who trained with simple single-joint exercises, hypertrophy occurred early whether leg or upper body exercises were performed. Quadriceps CSA, as measured by ultrasound (Young, 1983) or magnetic resonance imaging (MRI) (Higbie, 1996)increased by 5-6.6% following 5-10 weeks of unilateral knee extension training, and upper arm CSA, as measured by CT, increased by 5.4-7.9% following 6-16 weeks of elbow flexor or extensor training (Cureton, 1988; Davies, 1988). Similar degrees of early hypertrophy have been observed in males following training with single-joint exercises: Quadriceps CSA, as measured by MRI (Narici, 1989) or CT (Jones, 1987), increased by 5- 8.5% following 9-12 weeks of unilateral knee flexion training, and upper arm CSA, as measured by CT (Cureton, 1988; Brown, 1990)or MRI (McCall, 1996), increased 7.9-17.4% following 12-16 weeks of elbow flexion or extension training."
2. Lack of or a lower level of early size gains with compound movements: "In contrast to the above training studies employing simpler exercises, training programs using complex exercises have resulted in little or no muscle hypertrophy early in training. Females who trained using mainly multi-joint exercises of squats and leg press had significant changes in lower extremity strength by 8-16 weeks, but no change in thigh girth or CSA (Cureton, 1988; Staron, 1989). Studies of males who trained using mainly squat or leg press exercises have, similarly, resulted in significant gains in strength, but little hypertrophy after 7-16 weeks of training when quadriceps CSA was measured by ultrasound (Dons, 1979) or CT (Cureton, 1988;Brown, 1990), or when muscle fibre size was measured from biopsy samples (Hakkinen, 1983). Thus, it seems that muscle hypertrophy is delayed when complex exercises are used for training. This may be due to a more prolonged neural adaptation compared to simpler exercises."
3. Greater motor unit activation for a given muscle with isolation movements: "During simple exercises, motor unit activation, as determined by the interpolated-twitch technique, is close to 100% in the untrained state and changes little with training. Determination of motor unit activation during complex exercises would be technically difficult, but it is possible that when compared to simple exercises, activation is not as complete and an increase in this parameter would require longer training periods." This is also supported by at least one other study which found that an isolation exercise (say tricep extension) completed before a compound movement (say bench press) that also used the same muscle, had a greater force decrement in compound exercise than the converse (i.e. bench press completed before tricep extensions had less of an effect on tricep extension performance). This may suggest that triceps are more wasted with the tricep extension exercise than with the bench press."
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Complex problems have simple, easy to understand, wrong answers.
