Conjugate exercises are analogs of the same exercise in which the strength gained in the one exercise successfully transfers through to the other exercise. An example of this would be completing a bench press program and discovering that your floor press, incline press, and shoulder press increased as well.
If your bench press increased 50 lbs, you might notice an increase of around the same for your floor press, maybe 35 lbs in your incline press, and at least 20 lbs in your shoulders press. Of the three exercises the shoulder press would be the least likely conjugate choice, but nevertheless the type of exercise (pushing) and the muscles involved are nearly identical.
Conjugate exercises have many benefits. The biggest benefit is that the same goal can be achieved by a different means. For example, if my goal is to bench press 350 lbs I don’t need to specialize in the bench press to do it. In fact, I could use the bench press infrequently reserving it to assess strength and practice technique using submaximal weight.
The bulk of the heavy work can be done using conjugate exercises that are more effective and safer. The floor press restricts the range of motion a lifter can lift, but prevents the shoulder from being over stretched. Small lifters can benefits from this as the bar has to reach a greater depth as they lack the big barrel chest a 300 lbs powerlifter has. The increased longevity of this lifters’ career from reducing stress on the shoulder will allow more time for this athlete realize their goal.
Bench Press lockouts can also be used to gauge an increase in progress. If you can pin press 400 lbs for several reps and your 1 rep max PR in the bench press is 250 lbs and you gain 100 lbs on your in press, you most certainly would expect to break your previous 1 rep max PR. Certainly not all 100 lbs of strength in the pin press would transfer, but an expectation that the athlete would gain 25 lbs to their bench press max is reasonable.
Training with unorthodox exercises like the pin press isn’t common, but the huge weight you can handle allows consistent increments in resistance to be added. Anyone can almost expect to add 5 lbs to their pin press each workout similar to how any given person could more than likely add 5 lbs to their barbell shrug every workout for prolonged periods of time.
So instead of making 10 failed attempts trying to increase your max PR, switch to a conjugate that will allow you make increments. Regardless if the increase is neurological or actual muscle being gained, it is much easier to succeed at a conjugate than psychologically battle with continued failures.
Conjugates can also help an athlete prepare for a tournament physically and mentally. If they did a 400 lbs squat at their last powerlifting tournament and recall being able to handle 255 lbs in the box squat for 3 reps the previous week, chances are in the future they will be able to start gauging their abilities based on this conjugate.
At the next tournament if they are able to box squat 255 lbs for 7 reps, they know for certain they are going to set a new personal record and might even be able to use a 1 rep max calculator using this conjugate as an estimate.
Regardless of the reason for using conjugate exercises, the important thing to remember is that they provide an alternative pathway to accomplish the same goal. The strength gained in one exercise successfully transfer over to another.