≈12 week strength training program significantly increased hamstring strength in NCAA DIII women's soccer athletes

Introduction

Strength training is vital for any injury risk mitigation and athletic performance program. Reproducible academic studies have established the parameters necessary for sufficiently developing strength. Lifting in excess of 80% of one’s one-repetition maximum across multiple sets with a low-to-moderate amount of repetitions is needed to spur true strength gains (i.e. 3-6 sets or 1-5 reps at 80-95% of 1RM).

In short: Lift heavy, get strong.

Late last fall, I was approached by the (now former) head women’s soccer coach at the small NCAA Division III college I teach at with a broad request: “I want my team to get stronger.” We had come close to qualifying for the yearly national tournament over the last handful of seasons but had not been able to achieve the goal. Lacking sufficient strength as a team was identified as one of the primary barriers to qualifying during the end-of-season coach’s meetings, so they turned to me for some help. Additionally, the team suffered multiple nagging musculoskeletal injuries that fall, so injury risk mitigation was determined to be a secondary outcome of interest.

Methods

The program I developed was dubbed “Project IronWolf” because who doesn’t like a good codename?

There are quite a few barriers to success for most programs at the DIII level including resources, time, and equipment/building availability. To add an extra layer of complexity, many of the athletes on the team had little weight training experience, even since entering college. As such, the program I developed was ultimately quite basic and condensed with the primary goal of developing general strength throughout all muscle groups.

Prior to beginning the program, each athlete completed force plate and dynamometry assessments to determine baseline values for the countermovement jump (CMJ; power), isometric mid-thigh pull (IMTP; strength), quadriceps strength, and hamstring strength. Dynamic Strength Index values were derived from CMJ and IMTP data and quad-to-hamstring strength ratios were calculated bilaterally. These data were used to determine the extent of lower extremity strength (and power) improvement and, thus, to infer a reduction in lower extremity injury risk. True one-repetition max testing was not conducted due to athlete safety concerns. One-repetition max values were approximated by using a modified three-repetition max testing protocol. The athletes increased weight for up to three sets of each lift until they reported at least an 8/10 rating of perceived exertion. That weight was then used to estimate their one-rep max.

Twenty-two athletes completed two supervised and one unsupervised (read: optional) 30-45 minute training sessions per week for approximately 12 weeks. Below is the general template for all exercises complete; if time allowed, a fourth exercise was added with sets ranging from 3-4 and reps 8-15. Examples of fourth exercises included: landmine single-leg RDLs, box jumps, plyometric medball variations, Nordic curls, Nordic quads, face pulls, etc.

Results

Of the 22 athletes, eight completed all pre- and post-program strength assessments. Below are the relevant results:

• CMJ Peak Force

  • Pre: 116.3 +/- 38.2 kg

  • Post: 143.1 +/- 38.9 kg

  • 23.0% improvement; p = .056 (not statistically significant)

• IMTP Net Peak Force

  • Pre: 74.3 +/- 17.7 kg

  • Post: 80.7 +/- 20.8 kg

  • 8.6% improvement; p = .119 (not statistically significant)

• Dynamic Strength Index

  • Pre: 1.6 +/- 0.6

  • Post: 1.8 +/- 0.5

• Left Quadriceps Strength

  • Pre: 212.5 +/- 45.5 N

  • Post: 231.6 +/- 18.8 N

  • 9.0% improvement; p = .251 (not statistically significant)

• Right Quadriceps Strength

  • Pre: 208.3 +/- 45.6 N

  • Post: 235.6 +/- 24.0 N

  • 13.0% improvement; p = .195 (not statistically significant)

• Left Hamstring Strength

  • Pre: 158.4 +/- 25.0 N

  • Post: 202.4 +/- 29.0 N

  • 27.0% improvement; p = .000 (statistically significant)

• Right Hamstring Strength

  • Pre: 160.8 +/- 34.5 N

  • Post: 210.2 +/- 38.5 N

  • 30.8% improvement; p = .002 (statistically significant)

• Left Hamstring:Quad Strength Ratio

  • Pre: 0.8 +/- 0.3

  • Post: 0.9 +/- 0.2

• Right Hamstring:Quad Strength Ratio

  • Pre: 0.8 +/- 0.2

• Post: 0.9 +/- 0.2

Discussion

Overall, this program and methods were not academically rigorous enough to warrant publication in a journal (hence why I’m publishing it here). However, the results were still encouraging.

The athletes saw significant increases (p = .000, .002) in hamstring strength, which should reduce the risk of experiencing hamstring and adductor muscle strains—two common injuries in soccer—and potentially significant knee injuries such as ACL ruptures. (The hamstrings provide dynamic stability against the anterior translation of the tibia, one mechanism that is causative of ACL tears.) However, all other testing did not report a statistically significant increase in strength or power. The CMJ approached a statistically significant improvement (p = .056) but approaching significance is not significant.

I was a little surprised that quadriceps and IMTP strength did not improve more; however, I think this could be attributed to a lack of true one-repetition max testing, the overall lack of exercise volume focusing on the quadriceps, particularly in isolation, and the small sample size. With a new coaching staff implemented this fall, we will have more time and resources cleared for strength training. Additionally, the athletes will have experience with a collegiate strength training program. These two factors will allow for the above program to be modified to include more resistance training volume with even greater emphasis placed on improving quadriceps and gluteal strength (i.e. knee extensions, hip thrusts, etc.).

Finally, while the overall goal of the program was to increase strength, it could be argued that the athlete’s power increased more despite little emphasis placed on plyometric exercises. This can likely be explained by power increasing via lifting very heavy or completing explosive exercises (i.e. plyometrics). In physics, power is defined as the amount of work completed over time, with work the product of force and displacement. In short, power can be increased by either increasing one’s force production (i.e. strength) or by reducing the time required to complete a task (i.e. plyometrics). Soccer is inherently a power-driven sport (kicking, jumping, cutting, sprinting) so I don’t see this increase in power as a negative.