Most studies of weightlifting are done on students or relative beginners; naturally the untrained will show a larger response than subjects who have been training for years.
Trainers have come up with a variety of complex routines to get experienced lifters past a plateau where they seem to be unable to make further gains. One of the more logical of these is Pre-Exhaustion (PreEx) training, which targets the strongest link muscle of a compound exercise with isolation exercise before the compound exercise, with the goal of saving the weak link muscles so that the compound exercise will fully exhaust the already-trained stronger muscle.
A new study, “The effects of pre-exhaustion, exercise order, and rest intervals in a full-body resistance training intervention” by James Peter Fisher, Luke Carlson, James Steele, and Dave Smith blows that out of the water. Fully-trained subjects were given either routines in proper order for PreEx training or routines not in such order. The result was that the order of exercise made no significant difference in gains or performance.
It is generally true that compound exercises are more time-efficient, and a series of compound exercises (like pullups, squats, or deadlifts) done with intensity and to exhaustion is likely to produce better gains in less workout time than a mix of isolation and compound exercises. There are reasons to do isolation exercises — when you do have a weak link needing further strengthening to catch up, or when injury reduces ability to do compound exercises — but they should not occupy much of your gym time.
Pre-exhaustion (PreEx) training is advocated on the principle that immediately preceding a compound exercise with an isolation exercise can target stronger muscles to pre-exhaust them to obtain greater adaptations in strength and size. However, research considering PreEx training method is limited. The present study looked to examine the effects of a PreEx training programme. Thirty-nine trained participants (male = 9, female = 30) completed 12 weeks of resistance training in 1 of 3 groups: a group that performed PreEx training (n = 14), a group that performed the same exercise order with a rest interval between exercises (n = 17), and a control group (n = 8) that performed the same exercises in a different order (compound exercises prior to isolation). No significant between-group effects were found for strength in chest press, leg press, or pull-down exercises, or for body composition changes. Magnitude of change was examined for outcomes also using effect size (ES). ESs for strength changes were considered large for each group for every exercise (ranging 1.15 to 1.62). In conclusion, PreEx training offers no greater benefit to performing the same exercises with rest between them compared with exercises performed in an order that prioritises compound movements.
Further discussion of PreEx:
Pre-exhaustion (PreEx) training is an advanced resistance training (RT) method where 2 or more sequential exercises are performed in immediate succession. Whilst Jones (1970) is often credited for the hypothesis and application of PreEx RT, he suggests that the original concept existed prior to his description. The PreEx method is based upon the hypothesis that a point of momentary muscular failure (MMF) in a compound exercise occurs when the weakest muscles involved are no longer able to apply the required force to continue the exercise (Jones 1970). As such the “target” muscles can be “pre-exhausted” with an isolation exercise before moving immediately to a compound exercise. For example, the biceps might be the “weak-link” in a pulling exercise though the target might be to train the latissimus muscles. With this in mind, it is suggested to pre-exhaust the target muscles using an isolation exercise immediately prior to a compound exercise. It is hypothesised that this provides greater stimulation to the target muscles. Jones (1970) notes that “during the brief period while your weak-link muscles are actually stronger than your target muscles, you can take advantage of that momentary condition to use the strength of the weak-link muscles to train the target muscles much harder than would otherwise be possible.”1 Since evidence suggests training to MMF maximally recruits motor units and produces greatest gains in muscular strength (Fisher et al. 2011) and hypertrophy (Fisher et al. 2013a), the notion of attaining a greater fatigue to maximise adaptation appears logical.