The Effect of Protein Supplementation Improve Quadriceps Muscle Strength with ACL Reconstruction


Do-Kyung Kim1, Geon-Park2, Jae-Ho Yu*3

1 Dept. Sports Medicine, Samsung Medical Center, Korea

2Dept. Sports Medicine, Samsung Medical Center, Korea

3Dept. of Physical Therapy, ASI|KR|KS002|ASAN, Sunmoon University, Korea

*Corresponding Author E-mail:,,



Background/Objectives: The Anterior cruciate ligament injury is known to develop muscular weakness in the quadriceps. Especially, the weakness of the quadriceps muscle might be associated with increasing functional instability Protein supplementation can enhance the training outcomes of subjects, but it is not clear if there are benefits after ACL reconstruction. The aim of this study was to determine the effect of 12 weeks of rehabilitation exercise that only measured quadriceps muscle strength with supplementation of whey protein versus non supplementation.

Methods/Statistical analysis: The thirty men (mean age: 25.4±6.1yr) who underwent ACL reconstruction were divided into two groups. The first group was proteins supplementation exercise group (PSG, n=15) and another group was non-protein supplementation exercise group (NPSG, n=15).

All groups had gotten right on the rehabilitation exercise for 12 weeks after the surgery with ACL reconstruction via hamstring-tendon auto-graft. Outcomes were measured the quadriceps strength on either side by CSMI isokinetic testing device.

Findings: PSG showed significantly improvement in quadriceps muscle strength compared with NPSG. In PSG, the quadriceps strength deficit reduced 37.4±16.8% to 22.5±6.5% at 60°/sec and 29.2±13.1% to 18.5±7.9% at 180°/sec whereas NPSG showed reduced by 36.1±15.6% to 28.5±8.8% at 60°/sec and 27.8±14.7 % to 21.9±9.3% at 180°/sec, respectively.

Improvements/Applications: The combination of protein supplementation and exercise inanterior cruciate ligament reconstruction surgery has effective impact on quadriceps muscle strength.


KEYWORDS: Protein supplementation, ACL reconstruction, Quadriceps strength, Isokinetic, Strength deficit.




Anterior cruciate ligament (ACL) sprain or tear are the relatively commonly knee injury in sports activities1. Also, it results in mechanical and functional instability in most physical and sports activity, and patients often get it difficult to return to fully functional activity after injury. Surgical treatments of the rupture of ACL have been prevented knee joint instability and supported the function of ligament torn. However, many patients have experience weakness of the knee muscles after ACL reconstruction that would be unable to have functional ability2. Palmier-Smith et al. suggest that quadriceps strength deficits varied from 24 to 40.5% in six months, and quadriceps deficit also varied from 10 to 27% after 12 months3.


For this reason, several studies suggested that recovery of quadriceps strengthen and knee functional ability lead to improve outcomes in ACL reconstruction4,5. The recovery of muscle strength and masshas been discussed to be the main target accordingly towards the quadriceps muscle. Recent study reported that adequate nutrition is the important including exercise to improve physical function level. In particular, amino acids, one of the protein components, are essential for improving muscle strength6.Essential amino acids are stimulators of protein synthesis and they are caused to increase muscle strength and function in human body. Whey proteins are part of the amino acids that contribute to stimulate the synthesis of muscle7. Therefore, we considered that we could induce muscle strength through proper exercise training and whey protein supplementation.


The purpose of our study was to examine the difference between whey proteins supplement and non-supplement groups with rehabilitation exercise that underwent anterior cruciate ligament reconstruction.



2.1. Subjects:

From April 2014 to May 2015, 30patients were operated using arthroscopic ACL reconstruction with hamstring auto grafts (semitendinosus and gracilis tendon grafts).Exclusion criteria were previous ACL and posterior cruciate ligament reconstruction, collateral ligament repairs and previous history of knee surgery.

The study included30 men (mean age: 25.4±6.1yr) were divided into two groups, the first group was a protein supplementation exercise group (PSG, n=15) and another group was non-protein supplementation exercise group (NPSG, n=15).


2.2. Protein Supplementation

The nutritional supplements in our study are whey proteins (Resource; GNC, USA). Every rehabilitation exercise training session, subjects (PSG) received total 40g of whey protein that supplied20gof whey protein intake with 200-300 ml of water before and after each two hour from training, so the total of 40gof whey protein supplementation with the water was recommended that the day of whey protein intake had been started immediately after the surgery for 12 weeks. Even if they could not do the rehabilitation exercise, they took the whey protein in the daytime.


2.3. Rehabilitation exercise program:

Both groups postoperative rehabilitation exercise program used a same protocol. In the immediate postoperative, isometric quadriceps exercise and range of motion exercise were performed. 2-4 weeks after surgery, 90° of knee flexion, full extension motion and bike for ROM were started. Post-op 4-6 weeks, full ROM and close chain exercise and partial weight bearing allowed. At7-10 weeks after surgery, progression in strength power and increase agility permitted. Post-op 10-12weeks, maximum strength training and port-specific activities were allowed if there was no effusion, pain, or knee instability. The rehabilitation exercise program showed in Table 1.


Table 1.Anterior cruciate ligament reconstruction rehabilitation on protocol

Postoperative Period

Rehabilitation goals

0-2 week

Full knee extension ROM Quadriceps strengthening

2-4 week

Progress ROM

4-6 week

Full ROM by 6week Progress closed chain exercise

6-10 week

Full weight bearing walking Progress weight training

10-12 week

Slow form running Agility training

ROM; Range of Motion


2.4. Muscle Strength:

The strength of the quadriceps muscles was evaluated isokinetic system (CSMI Medical Solutions, MA, and USA) and dynamometer at speeds of 60°/secand 180°/sec. The value of maximal peak torque (Nm) for each dynamometer speed was calculated and used for percent of quadriceps muscle strength deficit with the uninjured side.


2.5. Statistical analysis:

For Statistical analyses, we used SPSS version 20.0. Parametric variables investigate the change in quadriceps strength deficits between PSG and NPSG, a repeated measures analysis using independent sample t-test. All statistical test were considered statistically significant was set at p<.05



Baseline characteristics of the 30 subjects who completed the study are: PSG (172.8±4.5 cm and 74.2±7.6 kg, n=15) and NPSG (173.4±5.2cm and 75.3±8.2 kg, n=15). There were no differences between the PSG and NPSG for any of the baseline measurements.


The deficit of quadriceps muscle strength was measured as the different percentage between the injured and uninjured knees. Definitely both groups has deficit of quadriceps muscle strength between injured and uninjured knees. After 12 weeks rehabilitation exercise training session, In PSG, the quadriceps strength deficit reduced 37.4±16.8% to 22.5±6.5% at 60°/sec and 29.2±13.1% to 18.5±7.9 at 180°/sec whereas NPSG showed reduced by 36.1±15.6% to 28.5±8.8% at 60°/sec and 27.8±14.7 % to 21.9±9.3% at 180°/sec, respectively. The quadriceps muscle strength was significant differences between the both groups at 60°/sec and 180°/sec. PSG showed a significantly greater improved whey protein supplementation patient than controlled NPSG at 60°/sec and180°/sec are shown in Table 2.


Table 2. Comparison of quadriceps muscle strength deficits



Pre rehabilitation

Post rehabilitation

Main effect(time)

Group-time interaction
































PSG: Protein Supplementation exercise Group,

NPSG: Non Protein supplementation exercise Group

* Indicates significant (p<0.05) difference between the two groups.


Our study found were that rehabilitation exercise combined with protein supplementation more gained in quadriceps muscle strength in ACL reconstruction patients. Outcomes confirmed the benefits of the Protein supplementation exercise group was significantly lower deficits with quadriceps muscle strength compared to the patients who did only exercise program. Those results indicate that protein supplementation has a positive effect upon muscle hypertrophy and strength deficit outcome after ACL reconstruction exercise program.


In recent studies, they mostly reported that quadriceps strength deficit varied from 24-40.5% in 6months post-ACL Reconstruction. And another studies reported that deficit in extensor muscle strength had 10-27% in1 year post surgury3. This lack of quadriceps strength reduces knee function and increases the risk of re-injures. In addition, quality of life is reduced in activities of daily. Thus, the recovery of quadriceps muscles strength is one of the most important factors after ACL reconstruction8). It could be speculated that the recovery of especially the quadriceps is important during the initial rehabilitation intervention, and thus for the overall clinical outcome in ACL injured patients, because this specific muscle is the part of the quadriceps muscle with most influence on the knee-joint stability9.


The main findings of the present study were that rehabilitation exercise combined with protein supplementation more gained in quadriceps strength in ACL reconstruction patients. Thus, protein supplementation with rehabilitation exercise training group resulted in quadriceps strength deficit reduced 22.5% at 60°/sec and 18.5% at 180°/sec. In contrast, non-supplementation rehabilitation exercises group showed 28.8% at 60°/sec and 21.9% at 180°/sec, respectively.


The total amount of protein supplementation during the periods of muscle gain has been widely discussed, and the whey protein could have inhibited protein catabolism that increased the muscle strength. The explanation of underlay metabolism for muscle fiber hypertrophy with protein synthesis is stimulated to the rate in exceeds muscle protein breakdown system, thereby inducing net protein balance positively. These papers have been reported that increased circulating amino acids will have more positive net protein balance at rest10.


Resistance training has definitely stimulation effect on protein synthesis11. Yang reported that supplied 40g of whey protein daily with general rehabilitation exercise group had higher impact than the other two groups12. Pennings et al. also reported that supplied 35g of whey protein group had higher amino acid absorption, plasma insulin, protein synthesis stimulation comparing with the other 10g or 20g of whey protein groups13. Every rehabilitation exercise training session, PSG had supplied 40g of whey protein that received 20g of whey protein with 200–300 ml of water before and after training, so the total of 40g of whey protein supplementation with the water was recommended that whey protein was started the day after the surgery in the whey protein group for 12 weeks.


In a related study protein ingestion time, it has further indicated that the acute effect of protein supplementation on muscle anabolism would be greater impact if the whey protein is ingested before the training bout 14. In the another study of protein supplementation time, the ingestion of protein immediately after resistance training led to the muscle hypertrophy, whereas the postponed protein supplementation delay for 2 hours group did not15.


In the present training study, we suggest that protein supplementation group had 20g of whey protein twice a day just before and after rehabilitation exercise training session for optimized anabolism. As a result, the present study demonstrated that the combination of whey protein supplying and rehabilitation exercise training for 12 weeks in the early postoperative period have great beneficial effects on the knee muscle strength in ACL reconstruction.



The fact that the muscle strength changes were only different between protein supplementation groups at the knee extensor strength. And as results, these are indicated that whey protein supplementation has a positive effect upon knee muscle strength outcome after exercise training program in ACL reconstruction patients.



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Received on 22.06.2017          Modified on 20.07.2017

Accepted on 23.08.2017        © RJPT All right reserved

Research J. Pharm. and Tech. 2017; 10(9): 2871-2874.

DOI: 10.5958/0974-360X.2017.00506.6