Strength Does Not Equal Rate of Force Development

Strength Does Not Equal Rate of Force Development

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The most common complaint we hear at the end of ACL rehab is that athletes feel slower. So how do you get your speed back at the end of ACL rehab? The key is working on your rate of force development.

Rate of force development is considered an important aspect of neuromuscular function during sporting activities both from a performance standpoint and an injury risk reduction standpoint. This is not to be confused with strength production as they are distinct qualities both clinically and physiologically. It has been reported that explosive strength, or rate of force development, may depend more upon levels of neural excitation while maximal strength is dependent more upon muscle contractile mechanisms1,2. This is supported clinically as Angelozzi et al. reported the average quadriceps Maximal Voluntary Isometric Contraction (MVIC) 6 months after ACL reconstruction was restored to 97% to the baseline value while average rate of force development at 30, 50, and 90% MVIC was 80, 77, and 63%, respectively3.  This finding was also supported by Knezevic et al. who found larger asymmetries in rate of force development at 50ms, 150ms, and 250ms than maximal force production at 4 months post ACLr4. 

It is important to note that these findings were apparent with the use of an isometric leg press utilizing ankle/knee/hip joints3 as well as the use of isometric isokinetic dynamometer measuring quadriceps and hamstrings rate of force development4. Additionally, these two studies looked at BTB and hamstring autografts. In agreement with the previously mentioned two studies, it was also found that rate of force development and time to peak torque, but not maximal strength were related to subjective knee function5 as well as gait kinetics linked to osteoarthritis development4.

Overall, these findings appear to suggest that force production and the rate at which it is produced are complimentary, but distinct neuromuscular qualities and both should be assessed along the rehabilitation continuum and decision making for return to sport3, 4, 5, 8,. One possible explanation to why rate of force devlopment appears to be lacking behind strength measures is that rehabilitation typically does not adequately implement interventions aimed at improving rate of force devlopment to the level of that required for sporting activity. Another explanation, from a physiological standpoint, is that a healthy ACL is a proprioceptive (senses body position and movement) organ providing afferent (information sent from the body to the brain) input to the nervous system about position. After ACL injury, there is disruption in this communication between the knee joint and the nervous system which may alter efferent (information sent from brain to the body) kinetics and kinematics. Particularly, the attenuation of type 1a afferents may decrease recruitment of high threshold type II muscle fibers which may contribute to lower rate of force development after injury9.

In addition to differences being detected in rate of force development during isometric testing, it has been noted that different functional hop tests may be more related to quadriceps rate of force development or strength. The single leg hop for distance (SLHD) test is commonly used as part of a test battery following ACLr to identify limb symmetry index (LSI) and functional ability. Interestingly, it has been found that this test was more associated with quadriceps strength than rate of force development10. On the other hand, the single leg vertical jump (SLVJ) test was more associated with quadriceps rate of force development than strength. This finding is interesting to note; however, it may be influenced by the fact that participants were allowed to move their arms in the SLHD while in the SLVJ they were not.

Due to the finding that strength and rate of force development have been shown to be complimentary, but distinct measurements especially following ACLr, it is critical that they are both assessed throughout the rehabilitation process to gauge progression and guide rehabilitation strategies to address lasting impairments. The use of objective testing to track this data is crucial to optimize safe return to play. Without objectively tracking, we are just guessing.

Be sure to check out our next post where we discuss other variables that play a role in the high rates of ACL reinjury and how we can better address it.

Are you an athlete who recently suffered an ACL injury, is currently undergoing ACL Rehabilitation or are looking for that next step to bridge the gap from ACL physical therapy to Return-to-Play? We work with all types of athletes recovering from ,ACL injuries, taking them through a detailed process to return them back to sport safe and prepared to play!  We focus on areas such as strength restoration, movement re-education and objective testing with the latest strength and force plate technology to assess progress and readiness for return-to-play. Learn more about our approach to ACL Rehabilitation, or reach out today to schedule a free consultation to see if we can help you.

Learn more about the ForceDecks technology we use to assess our athletes.

References:

  1. Oliveira FB Oliveira AS Rizatto GF Denadai BS. Resistance training for explosive and maximal strength: Effects on early and late rate of force development. J Sports Sci Med. 2013;12(3):402-408
  2. Folland JP, Buckthorpe MW, Hannah R. 2014. Human capacity for explosive force production: Neural and contractile determinants. Scand. J. Med. Sci. Sports 24: 894-906
  3. Angelozzi M, et al. Rate of force development as an adjunctive outcome measure for return-to-sport decisions after anterior cruciate ligament reconstruction. J Orthop Sports Phys Ther. 2012;42(9):772–80.
  4. Knezevic OM, Mirkov DM, Kadija M, Nedeljkovic A, Jaric S. Asymmetries in explosive strength following anterior cruciate ligament reconstruction. Knee. 2015;21:1039–1045.
  5. Hsieh CJ, Indelicato PA, Moser MW, Vandenborne K, Chmielewski TL (2015) Speed, not magnitude, of knee extensor torque production is associated with self-reported knee function early after anterior cruciate ligament reconstruction. Knee Surg Sports Traumatol Arthrosc 23:3214–3220
  6. Blackburn JT, Pietrosimone B, Harkey MS, Luc BA, Pamukoff DN (2016) Quadriceps Function and Gait Kinetics after Anterior Cruciate Ligament Reconstruction. Med Sci Sports Exerc 48:1664–1670
  7. 14 Kadija M, Knezevic OM, Milovanovic D, Nedeljkovic A, Mirkov DM. The effect of anterior cruciate ligament reconstruction on hamstring and quadriceps muscle function outcome ratios in male athletes. Srp Arh Celok Lek. 2016;144:151–157. doi: 10.2298/SARH1604151K.
  8.  Beneke R, Taylor MJ. What gives Bolt the edge-A.V. Hill knew it already! J Biomech. 2010;43(11):2241–3.
  9. Konishi Y, Fukubayashi T, Takeshita D. Possible mechanism of quadriceps femoris weakness in patients with ruptured anterior cruciate ligament. Med Sci Sports Exerc. 2002;34((9)):1414–1418.
  10.  Pua Y-H, Mentiplay BF, Clark RA, Ho J-Y. Associations among quadriceps strength and rate of torque development 6 weeks post anterior cruciate ligament reconstruction and future hop and vertical jump performance: a prospective cohort study. J Orthop Sports Phys Ther. 2017;47(11):845–852.
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