Periodization in the rehabilitation of anterior cruciate ligament injuries

Knowingly or not, sports physiotherapists use periodization principles when they implement post-operative protocols. Jessica Montgomery explains how capitalizing on periodized training can improve ACL injury outcomes.

To successfully return to play, athletes recovering from anterior cruciate ligament (ACL) injuries must regain their preinjury level of strength, neuromuscular control, and power. These elements are necessary for both enhancing performance and decreasing re-injury risk. However, many clinicians don’t understand training program development concepts beyond the initial rehabilitation stages.

After decreasing pain and swelling, physios systematically progress a patient’s range of motion (ROM), strength, power, and speed depending upon the specific goals for each phase of rehabilitation⁽¹⁾. However, most protocols lack details and guidelines regarding the use and adjustment of resistance training variables within those periods⁽²⁾. Thus the latter phases, which should prepare athletes for return to play, may not provide adequate exercise dosing. Periodization serves as a meaningful strategy that physios can use in their program design to better bridge the gap between the treatment of an ACL injury and training for a return to play⁽³⁾.

Defining periodization

Strength and conditioning coaches periodize athletes’ training programs based on their competition cycle. A preparatory period focuses on developing a base level of conditioning emphasizing on muscular endurance, strength, and hypertrophy. Athletes achieve this through both general and sports-specific training. A transition phase follows, during which the athlete continues to build strength. Once the athlete establishes sufficient strength, they can progress to the power development necessary for competition.

Periodization is the planned manipulation of training variables (load, sets, and repetitions) to maximize training adaptations while minimizing fatigue⁽²⁾. Periodized programming utilizes the principle of overload, whereby the neuromuscular system adapts to unaccustomed loads⁽²⁾. While progressive overload is a well-established and widely used concept for strengthening, the variance of volume and intensity makes periodization more effective at improving athletic performance attributes, such as muscular strength, endurance, and power, compared with non-periodized training⁽⁴⁾.

Various models of periodization exist. The two most common are linear and non-linear or undulating. Linear periodization (LP) adjusts exercise volume and load across a series of predictable phases or mesocycles. This stepwise progression from one training stage to another based on intended goals is similar advancing a rehabilitation protocol from one stage of recovery to the next. Non-linear periodization (NP), on the other hand, involves a more frequent change of volume and load within a mesocycle.

Periodization of the phases of ACL rehabilitation

The initial post-operative phase of ACL rehabilitation focuses on pain and swelling management, restoration of ROM, quadriceps recruitment, and normalizing gait mechanics. Once an athlete meets these goals, they can begin a periodized resistance training program. To determine the appropriate load for an exercise prescription, clinicians must establish a one-repetition maximum (1RM) for each exercise. Injured or healing tissues pose a challenge to determining 1RMs when they require limited loading. In this instance, predictive models, such as the Oddvar Holten Curve, can be helpful. Instruct patients to perform repetitions to fatigue using a low load and then correlate that amount to estimate a 1RM (see figure 1).

Figure 1: Oddvar Holten Curve ⁽²⁾

The Oddvar Holten Curve estimates the percentage of the one-repetition maximum resistance using the number of repetitions to fatigue.

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Muscular endurance is the goal of the first phase of a periodized ACL injury rehabilitation program. Endurance provides a base for progression to hypertrophy and strength training⁽²⁾. The performance of high volume repetitions of low load over multiple sets is key to developing endurance (see table 1). Growth in neuromuscular efficiency is thought to contribute to the initial strength gains during this phase. Therefore, it is necessary to progress from endurance training to larger training volumes to evoke an increase in muscular size or hypertrophy⁽²⁾.

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Training Goal	Goal Repetitions	Sets	Load (% 1 RM)	Rest Period
	>12	2-3	<67	<  30 seconds
Hypertrophy	6-12	3-6	67-85	30 seconds to 1.5 minutes
Strength	<6	2-6	>85	2-5 minutes
Power-Single effort event-Multiple effort events	1-23-5	3-53-5	80-9075-85	2-5 minutes

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The hypertrophy period is characterized by a moderate to high number of repetitions of medium loads performed over multiple sets (see table 1). Strength development follows hypertrophy. Strength is a vital component of athletic performance as generating power is largely dependent upon force production. Building strength requires a further increase in load and a reduction in repetitions to six or fewer^(5,6). Strength enables a subsequent period of power development, which facilitates a successful return to sport. During the power phases, loads are high to train for maximal power output⁽¹⁾. For optimal power development, train across a full spectrum of loads and velocities with both single and multiple effort events⁽¹⁾.

For the athlete recovering from ACL reconstruction, an optimal schedule is three-days-per-week-with a program periodized for endurance, hypertrophy, and strength⁽²⁾. During the power phase, two sessions per week are sufficient. This schedule provides adequate recovery between sessions⁽²⁾. In regards to modifying training volume (repetitions, sets, load) within a specific training phase, the American College of Sports Medicine recommends changes made in increments of 2.5% to 5.0% per week to avoid overtraining (see table 2)⁽⁷⁾.

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Weeks 4-8: Endurance	Rest, 30-45 seconds
Straight leg raises, Leg Press, Step-ups, Dumbbell squats, Prone leg curl, Physioball bridge	3 x 15-20
Sidelying hip abduction, Supine bridges, Clamshells	3 x 20-30
Crabwalk	3 x 15 steps each direction
Weeks 8-12: Hypertrophy	Rest, 45 seconds-1 minute
Leg Press	3-4 sets x 12 repetitions (or failure)
Step-ups, Dumbbell squats, Lunges	3-4 sets x 10-12
Single leg squats, Prone leg curl, Physioball bridge, Physioball curl	4x12
Weeks 12-16: Strength	Rest, 2-3 minutes
Barbell back squats / front squats, Deadlift, Leg Press, Lunges, Nordic hamstring	3-4 sets x 6-10
Prone leg curl	4 x 8-12
Physioball bridge / curl / curl to bridge	3 x 6-10 each
Weeks 16-24: Conversion to Power	Rest, 3-5 minutes
Squat jumps, Lateral leaps, Box jumps	3 x 6
Scissor jumps	3 x 4 each leg

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Choosing the right periodization model

Linear periodization allows for the stepwise progression of training parameters predictably for both the athlete and clinician, thus taking the guesswork out of loading and repetition schemes⁽¹⁾. This kind of plan can be advantageous for patients who have insurance-based limitations. These athletes will need to work at home or with a school-based trainer to complete the lion’s share of their rehabilitation. The NP model addresses many training parameters simultaneously, allowing for prioritization of an athlete’s deficits. While more frequent fluctuation in volume and load may lead to better neuromuscular adaptations, there is also potential for the inadequate development of each performance characteristic⁽¹⁾.

Comparisons between linear and non-linear periodization models remain limited, with no definitive conclusions regarding a superior or preferred method^(1,2). Regardless of which model a clinician chooses, each program must follow the principle of specificity. Exercises must be tailored to the biomechanical and physiological demands of an athlete’s sport⁽⁸⁾.

Key takeaways

• Periodized strength training regimens demonstrate improved outcomes compared to non-periodized programs⁽²⁾.
• When equated for volume and intensity, there are no significant differences in strength gains between LP and NP models.
• In the ACL injury population, periodized rehabilitation programs may allow for better integration of an athletes’ needs to facilitate a successful return to play⁽³⁾.

References

1. Int J Sports Phys Ther. 2015;10(6):734-747.
2. Sports Health. 2010;2(6):509-518.
3. Med Princ Pract. 2020 Dec 2:1-8.
4. J Strength CondRes: 2009 Mar; 23(2): 513-523.
5. Essentials of Strength Training and Conditioning. Champaign, IL: Human Kinetics; 2016.
6. Int J Sports Phys Ther. 2018 Apr;13(2):293-305.
7. Med Sci Sports Exerc. 2002;34:364-380.
8. Clinical Rehabilitation. 2018;32(9):1235-1248.