This is the second of a two-part blog series pertaining to energy systems, conditioning, and how they pertain to ACL rehab. This post will explain how conditioning plays an important role throughout the ACL rehab journey.
Cardiorespiratory fitness, or conditioning, holds immense importance across various athletic pursuits. Whether a sport is primarily aerobic (e.g., distance running), anaerobic (e.g., sprints), or involves a mix of energy systems (e.g., soccer), conditioning significantly influences an athlete’s performance. Furthermore, cardiorespiratory fitness acts as a barometer for cardiovascular health and general well-being, carrying implications for a person’s health throughout their life.
Conditioning for the ACL Athlete
In the context of ACL rehabilitation, conditioning often takes a backseat until the later stages when an athlete is striving to return to practice or performance. Considering that deconditioning can occur as quickly as 2-4 weeks after cessation of regular training, and that it can take anywhere from 4 to 12 weeks to see lasting adaptations with consistent training, then why isn’t conditioning emphasized more during all stages of ACL rehabilitation?
The lack of focus on improving or sustaining cardiorespiratory fitness during the initial stages of ACL rehab can likely be attributed to various factors. Clinicians and athletes usually prioritize the ACL and knee during rehab. Many clinics lack the time, equipment, or resources for consistent conditioning. In certain insurance-based practices, dedicating time to conditioning might not be deemed a “skilled service,” which can impact billing. Athletes may also lack access or knowledge to safely engage in consistent conditioning outside the clinic.
When can I start conditioning after ACL surgery if I can’t run yet?
When we think of conditioning, running often comes to mind. However, in ACL rehab, many athletes can’t safely resume straight-line running until about 3-4 months post-surgery. This extended period of time without conditioning puts athletes at a notable disadvantage when gearing up to return to their sport. Fortunately, various alternatives to running exist that can help maintain and enhance conditioning, even in the early post-operative stages. Tools like stationary bikes, bike ergs, row ergs, and ski ergs can all be adapted to safely engage the non-operative limb while adhering to motion and weight-bearing precautions.
For example, sliders or skateboards can be used to offload the surgical limb while using a row erg.
Benefits of Early Conditioning During ACL Rehab
The benefits of engaging in regular cardiorespiratory activity outside of sport-related reasons is extensively documented for its long-term health benefits in adults, adolescents, and children. These benefits include reduced risk of cardiovascular disease, cancer, improved body composition, enhanced cognitive function, and decreased all-cause and disease-specific mortality for individuals with chronic medical conditions. Notably, most adults and youth fail to meet minimum physical activity guidelines for both strengthening and conditioning in the United States.
Recommended physical activity guidelines for adults are:
- Aerobic Activity
- 150 minutes/week of mod-intensity and/or 75 minutes/week of vigorous-intensity
- Strength Training
- 2 days/week
Recommended physical activity guidelines for children and adolescents are:
- Aerobic Activity
- 60 minutes/day of mod-vigorous intensity
- Muscle Strengthening
- 3 days/week
- Bone Building
- 3 days/week
Viewing conditioning through the lens of meeting recommended physical activity guidelines provides a solid foundation to build upon before progressing to more complex, specific conditioning programs during the later stages of ACL rehab.
Elevating Your Conditioning Capacity
From a return-to-sport standpoint, maintaining or improving your baseline aerobic conditioning early on eases the process of refining sport-specific conditioning during later rehab stages, as you reintegrate into organized practices and competitions.
Think of Your Conditioning Capacity as a Skyscraper
Visualize your conditioning capabilities as a skyscraper. Your baseline capacity before surgery is at the 7th floor.
After surgery, your conditioning capacity takes a hit. If you did nothing on the conditioning front for a while, your baseline may drop all the way down to the 1st floor.
BUT, if you’re able to engage in some conditioning early after surgery, your baseline capacity won’t drop as much, maybe to only the 5th floor…
This puts you in a much better position to get back to baseline or improve upon your prior baseline during the middle and later stages of ACL rehab.
Making the climb back up easier in the long run.
What should my conditioning look like during the different stages of ACL rehab?
There isn’t a one-size-fits-all solution when it comes to conditioning throughout your ACL journey. It’s important that your therapist, athletic trainer, and coaches understand the demands of your sport or activity when it comes to structuring your conditioning. Conditioning should compliment your strengthening regimen. It’s also important to take time since surgery, weight-bearing precautions, ROM precautions, conditioning history, and current level of function into consideration when designing a conditioning program.
When it comes to structuring conditioning, we have a few primary variables that allow us to target specific energy system utilization. These variables include work interval duration, rest/recovery interval duration, frequency (times per week), intensity, and the modality or equipment used (if any). Think of these as dials on a guitar amp that we can turn up or down to target a certain system, or train repeated sprintability if we’re utilizing multiple energy systems.
To target specific energy systems, primary variables like work interval duration, rest/recovery interval duration, frequency, intensity, and equipment used (if any) can be adjusted. Work duration and intensity are inversely related, meaning shorter work periods allow for higher intensities and vice versa.
The chart below explains how duration, intensity, and energy systems are related.
| Duration | Intensity | Primary Energy System |
| 0-6 seconds | Maximal | ATP-PCr |
| 6-30 seconds | Near Maximal | ATP-PCr & Anaerobic Glycolytic |
| 30-120 seconds | High | Anaerobic Glycolytic |
| 2-3 minutes | Moderate | Anaerobic & Aerobic Glycolytic |
| > 3 minutes | Low | Oxidative |
Table 1 from ENERGY SYSTEM DEVELOPMENT AND LOAD MANAGEMENT THROUGH THE REHABILITATION AND RETURN TO PLAY PROCESS
During the early stages of ACL rehab, it’s recommended to prioritize aerobic conditioning. This generally involves low-to-moderate intensity, steady state work. Maintaining and building upon your aerobic conditioning base is crucial to focus on more sport-specific anaerobic focused training later on. Aerobic conditioning is also beneficial during the early stages because it’s generally easy to recover from, can help promote early surgical healing, is easily modifiable to adhere to weight-bearing and ROM precautions, and is a great way to gain a psychological advantage early in the ACL journey. Breaking a sweat and working hard is a great way to remind yourself that you’re still an athlete!
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“If you have a body, then you’re an athlete.”
Bill Bowerman
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As you progress through your ACL rehab, conditioning can progress towards including shorter intervals of work at higher intensities paired with appropriate bouts of recovery or rest intervals. You can transition to eventually include running and sprinting, and change of direction tasks that emulate the demands of sport while still making time to maintain your aerobic capacity.
When we program rest or recovery intervals that don’t allow for complete recovery between bouts of work, then we’re training repeat sprintability. This is the ability to repeatedly sprint or exert maximal/near-maximal effort with limited fatigue. The ability to sprint repeatedly with limited fatigue is common across multiple sports including footballs, basketball and soccer.
Conclusion
Conditioning is a crucial aspect of ACL rehabilitation that shouldn’t be neglected during any stage of the journey. Early engagement in conditioning can lead to improved long-term health outcomes and facilitate a smoother return to sport in the later stages of rehab. Remember to work with your rehab team and coaches to tailor a conditioning program that suits your needs and ensure a successful recovery.
References
Elgaddal N, Kramarow EA, Reuben C. Physical activity among adults aged 18 and over: United States, 2020. NCHS Data Brief, no 443. Hyattsville, MD: National Center for Health Statistics. 2022.
DOI: https://dx.doi.org/10.15620/cdc:120213
Lobelo F, Muth ND, Hanson S, Nemeth BA; COUNCIL ON SPORTS MEDICINE AND FITNESS; SECTION ON OBESITY. Physical Activity Assessment and Counseling in Pediatric Clinical Settings. Pediatrics. 2020 Mar;145(3):e20193992. doi: 10.1542/peds.2019-3992. Epub 2020 Feb 24. PMID: 32094289.
https://pubmed.ncbi.nlm.nih.gov/32094289/
Seehafer L, Morrison S, Severin R, Ness BM. A Multi-Systems Approach to Human Movement after ACL Reconstruction: The Cardiopulmonary System. Int J Sports Phys Ther. 2021 Dec 1;17(1):60-73. doi: 10.26603/001c.29451. PMID: 35024206; PMCID: PMC8720251.
https://pubmed.ncbi.nlm.nih.gov/35024206/
Morrison S, Ward P, duManoir GR. ENERGY SYSTEM DEVELOPMENT AND LOAD MANAGEMENT THROUGH THE REHABILITATION AND RETURN TO PLAY PROCESS. Int J Sports Phys Ther. 2017 Aug;12(4):697-710. PMID: 28900575; PMCID: PMC5534159.
