Acute Enhancement of Power Performance From Heavy Load Squats

Research Review: Acute Enhancement of Power Performance From Heavy Load Squats

By Sean Butler BS, CSCS, CES, DPT Student

Edited by Brent Brookbush DPT, PT, COMT, MS, PES, CES, CSCS, ACSM H/FS

Original Citation: Young, W. B., Jenner, A., & Griffiths, K. (1998). Acute enhancement of power performance from heavy load squats. The Journal of Strength and Conditioning Research, 12(2), 82. ABSTRACT

Why is this study relevant: Post-activation potentiation (PAP) is a phenomenon in which a muscle's force is acutely increased as a result of its contractile history (1). Research suggests that while fatiguing muscle contractions may impair performance, non-fatiguing muscle contractions may enhance performance (2). This 1998 study tested the effects of heavy barbell back squats on subsequent loaded countermovement jump performance. The results support the use of back squats to improve subsequent jump performance, with more pronounced effects in stronger individuals.

Caption: Back Squat (Half Squat)

Back Squat (Half Squat)

Study Summary

Study Design	Quasi-experimental, cross-over design
Level of Evidence	IIB Evidence from at least one other type of quasi-experimental study
Participant Characteristics	Demographics Gender: 10 males Age: 18 - 31 5RM Squat = (Mean +/- SD) 152.2 +/- 30.1 kg Participants volunteered to take part in the study Inclusion Criteria: One year of experience performing half squats Able to attend 2 sessions, 5 days apart Exclusion Criteria: N/A
Methodology	Testing was held on 2 separate days with 5 days between the test days. Day 1: Familiarization with testing procedures and 5 rep max (5RM) testing on the squat. Participants took part in a thorough warm up, completing 3 sets of 5 reps of the loaded countermovement jump (LCMJ), using a Smith machine with 19kg and the bar placed across the shoulders. A self-selected depth and speed were used for the jump, and participants were encouraged to bend their knees to absorb the impact. A 2-4-second rest period was used between jumps (intraset), and a 3-minute rest period was used between sets (interset) For 5RM testing, participants attempted to lift a weight for 5 reps. If successful, the bar weight was increased after a 5-minute rest period 3-4 trials were typically needed to determine each participant's 5RM Day 2: Assessment of LCMJ pre and post the back squat exercise All participants performed a warm up consisting of a 3-minute jog followed by lower body stretching. Participants then performed 1 set of half squats with 10 reps (50% of 5RM), followed by 2 sets of half squats with 5 reps (75% of 5RM), with each set separated by 3-minute rest intervals. After the warm up, participants began the testing sequence described below, with a 4-minute rest period between sets. LCMJ: 1 set x 5 reps x 19kg LCMJ: 1 set x 5 reps x 19 kg Half Squat: 1 set x 5 reps x 5RM LCMJ: 1 set x 5 reps x 19kg
Data Collection and Analysis	Data Collection: A sliding pointer was positioned over the bar on the Smith machine and read “0” when participants stood erect. The displacement of the pointer was measured during each jump. Participants were required to maintain shoulder contact with the bar during jumps. Any loss of contact was deemed a false trial and excluded from the analysis. The average jump height was used as the score for each LCMJ set. Statistical Analysis ANOVA with repeated measures was used to determine whether there was a significant difference between LCMJ sets. Scheffe Post Hoc test was used to compare interset LCMJs. An intraclass correlation and technical error of measurement were used to compare the two sets before the half squats to test for consistency.
Outcome Measures	Average LCMJ height.
Results	Set 1: LCMJ - 38.9 +/- 3.7 cm Set 2: LCMJ pre - 39.0 +/- 3.3 cm Set 3: LCMJ post - 40.0 +/- 3.5 cm Significance was set at (P<0.05) ANOVA revealed a significant time effect between pre and post conditions Post hoc analysis found no significant difference between the first two LCMJ sets LCMJ post was 2.8% greater than LCMJ pre 5RM strength was correlated with gain in performance (r = 0.73).
Our Conclusions	Heavy loaded back squats (5RM) are effective for increasing LCMJ height, with greater results in individuals with higher strength levels. Those looking to improve power output should incorporate heavy back squats prior to performing the desired activity.
Researchers' Conclusions	Power performance is enhanced when preceded by a set of half-squats using a 5RM load. Short-term performance enhancement has implications when designing competition warm ups.

Review & Commentary:

This study adds to a growing body of research on post-activation potentiation (PAP) by investigating the potential of the back squat to improve subsequent power activity performance. In addition, the findings suggest that PAP appears to favor stronger individuals. Based on the findings, human movement professionals may confidently recommend back squats to promote PAP, and should be aware that the effects of PAP may be larger for stronger individuals. This finding may also imply that PAP is more appropriate as a progression for more advanced athletes.

This study had several strengths, including:

Any performance increase due to the warm-up or repeated jumping was accounted for by having participants perform 2 jumps prior to data collection.
The repeated measures design allows athletes to act as their own control group. This design aids in accounting for confounding variables such as sleep, nutrition, training experience, genetics, etc.
All participants were familiar with the half squat exercise, with at least 1 year of experience; this aids in accounting for the potential of learning effects.

Weaknesses that should be noted prior to clinical integration of the findings:

A loaded countermovement jump (LCMJ) is not particularly functional - the biomechanics of the movement and load are not similar to sport. This may have implications on the generalizability of the study findings.
The small male-only sample size (n=10) makes the results less generalizable.
A single inter-set rest period (4 minutes) was tested between back squats and the LCMJ. A shorter or longer rest period may have augmented or diminished LCMJ performance.

Why This Study is Important:

This study adds to the growing body of research on PAP training by establishing heavy 5RM back squats as an effective exercise for eliciting an increase in performance on subsequent power activity. Further, this study may imply that stronger athletes have more to gain from PAP training.

How the Findings Apply to Practice:

The findings confirm that 5RM squats may be used for PAP, perhaps as part of strength/power supersets during high/intensity training periods. Further, because stronger individuals demonstrated larger increases in performance post 5RM squats, it may be appropriate to consider this training technique as a progression for more advanced individuals. Novice and/or weaker athletes may gain more from dedicated strength training prior to implementing PAP as described above.

Related to Brookbush Institute Content

As an evidence-based practical education company, the Brookbush Institute (BI) reviews and compiles research studies to aid in the design of recommendations and protocols for best practice. This study supports the use of "heavy" (1 - 5RM) back squats as an exercise for PAP style training, and also seems to support the idea that PAP is an advanced training method. Perhaps PAP is best used with athletes who have a solid foundation of training including one or more hypertrophy/max strength phases.

The BI recommends block periodized programming to improve performance, progressing from endurance/stability and hypertrophy/general strength phases to high-intensity training that includes max strength and power exercises. PAP training could be considered a training methodology for use during the second or third cycle through all appropriate phases, replacing traditional max strength or power training in that cycle.

Endurance/Stability: Increase reps or progress exercise (toward stability)
Hypertrophy/General Strength: Increase load, increase training volume (small progressions in exercise may be appropriate)
Max Strength: Increase load, and it may be appropriate to regress exercise to more stable environments
Power: Increase speed, height or distance

Below are videos related to the exercises in the study:

Back Squat

Bilateral Box Jump

Bibliography:

Robbins, D. W. (2005). Postactivation potentiation and its practical applicability: a brief review. Journal of Strength and Conditioning Research,19(2), 453.
Lorenz, D. (2011). Postactivation potentiation: An introduction. International Journal of Sports Physical Therapy, 6(3), 234.

Questions, comments, and criticisms are welcomed and encouraged -

Acute Enhancement of Power Performance From Heavy Load Squats

Research Review: Acute Enhancement of Power Performance From Heavy Load Squats

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