Contract-relax stretching between sets improved machine exercise reps
In short
In a randomized crossover study of 12 resistance-trained men testing 4 between-set conditions, contract-relax (CR) produced more reps and greater total load than passive rest or hold-relax (HR) in both pec deck and lat pulldown, with lower perceived exertion. Every set went to failure, so this exploratory result does not establish a benefit for heavy Big 3 singles or long-term muscle growth.
More work did not have to feel harder: contract-relax (CR) stretching between sets produced more reps and greater total load, with lower perceived exertion, than passive rest or hold-relax (HR) in pec deck and lat pulldown. That is an interesting result for accessory sessions. The abstract gives no rep counts or effect sizes, though, so it cannot tell you how many extra reps to expect.
How is contract-relax different from simply holding a stretch?
PNF stretching pairs a brief contraction of the muscle being stretched with relaxation into a deeper stretch. In the usual distinction, CR involves a contraction with movement against resistance; HR holds the contraction without joint movement. This describes the techniques in general, not the study's exact procedure. The abstract gives no contraction or stretch durations, so it does not support a timed routine.
What training did the researchers actually test?
The 12 trained men averaged about 20.8 years and 73.5 kg. Each completed all 4 conditions—combined PNF, HR, CR and passive rest—in a randomized crossover design, taking every butterfly (pec deck) and lat pulldown set to failure. Combined PNF outperformed passive rest for reps and total load only in the pec deck. It also lowered blood lactate at selected time points, yet felt harder. A lower lactate reading was not a reliable shorthand for an easier session.
What should you compare in your fairlift log?
If you try CR, use machine accessory sets that you already take to failure for hypertrophy work. Mark sessions with and without stretching, keep load, set count, rest length and range of motion consistent, and compare total reps, volume load (the sum of weight × reps), and perceived exertion. Look for a repeatable difference rather than declaring success after one session. Accessory volume does not add to your Big 3 1RM total or Muscle Index. Whether failure itself is useful is a separate question covered in our comparison of failure training and reps in reserve.
The authors describe the findings as exploratory because the sample included only 12 men and the study was not prospectively registered. Upper-body machine sets to failure cannot establish the same benefit for women, other age groups, heavy Big 3 singles or long-term muscle growth.
Frequently asked questions
How do contract-relax (CR) and hold-relax (HR) differ?
Both are PNF methods that briefly contract the muscle being stretched before relaxing into a deeper stretch. CR generally uses a resisted contraction with movement, whereas HR holds the contraction without joint movement. The study abstract does not specify the duration of either phase.
How many extra reps can contract-relax stretching produce?
In 12 resistance-trained men, CR produced more reps and greater total load than passive rest and HR in both pec deck and lat pulldown. The abstract reports neither rep counts nor effect sizes, so it cannot provide an expected number of extra reps for an individual.
Does combined PNF feel easier?
Combined PNF lowered blood lactate at selected time points in this study but came with higher perceived exertion. Its rep and total-load advantage over passive rest appeared only in pec deck, so it cannot be described as a generally easier option.
Can this improve Big 3 maxes and count toward Muscle Index?
The study tested upper-body machine sets to failure, not heavy Big 3 singles, so it does not establish a benefit for maximal lifts. Use your fairlift log to compare accessory reps and volume with and without stretching; Muscle Index uses Big 3 1RM records.
Source: PubMed