No Relationship Between Preoperative and Early Postoperative Strength After ACL Reconstruction

Context: All rehabilitative programs before ACL reconstructive surgery, which are focused on recovery of proprioception and muscular strength, are defined as prehabilitation. While it has shown that prehabilitation positively affects the overall outcome after ACL reconstruction, it is still controversial whether enhancing preoperatively quadriceps strength has some beneficial effect on postoperative strength, mainly during the first period. Objective: To determine whether there is any relationship between pre- and early postoperative quadriceps strength. Design: Case control. Setting: University research laboratory. Participants: Fifty-nine males (18-33 y; age: 23.69 (0.71) y) who underwent ACL reconstruction with patellar-tendon autograft were examined the day before surgery, at 60 and at 90 days after surgery. Main Outcome Measures: The limb-symmetry-index (LSI) was quantified for maximal voluntary isometric contraction (MVIC) of the knee extensor muscles and of the knee flexor muscles at 90° joint angle. K-means analysis was performed on either quadriceps or hamstrings LSI before surgery to classify the patients in high and low preoperative LSI clusters. Differences in postoperative LSI were then evaluated between the high and low preoperative LSI clusters. Results: Following surgery, there were no differences in the quadriceps LSI between patients with high and low preoperative quadriceps LSI. Sixty days after surgery, the hamstrings LSI was higher in patients with high than low preoperative hamstrings LSI (84.0±13.0% vs 75.4±15.9%; P<0.05). Conclusions: Findings suggest that quadriceps strength deficit is related to the ACL injury and increases further after the reconstruction without any correlation between the pre-operative and postoperative values. Therefore, it appears that there is no need to delay surgery in order to increase the preoperative quadriceps strength before surgery

Asymmetrical lower extremity loading early after ACL reconstruction is a significant predictor of asymmetrical loading at the time of return to sport

OBJECTIVES: The aim of this study was to examine whether asymmetrical lower limb loading early after anterior cruciate ligament reconstruction (1 mo) can predict asymmetrical lower limb loading at the time of return to sport (6 mos) and whether other early predictors as knee joint range of motion or maximal isometric strength affect this relationship. DESIGN: Ground reaction forces were measured during a sit-to-stand task 1 mo after anterior cruciate ligament reconstruction and a vertical countermovement jump 6 mos after anterior cruciate ligament reconstruction in 58 athletes. Other early postoperative measurements were knee joint range of motion (2 wks, 1 mo, and 2 mos after surgery) and maximal isometric strength of the knee extensor and flexor muscles (2 mos after surgery). Linear regression models were developed using side-to-side limb symmetry index (LSI) of countermovement jump as the dependent variable. RESULTS: LSI of sit-to-stand task 1 mo after surgery was a significant independent predictor of LSI of countermovement jump 6 mos after surgery. After accounting for deficits in knee joint range of motion and LSI of maximal isometric strength (ΔR² = 0.35, P < 0.01), LSI of sit-to-stand task predicted LSI of countermovement jump (ΔR² = 0.14 P < 0.01). CONCLUSIONS: Asymmetrical lower extremity loading 1 mo after anterior cruciate ligament reconstruction is an early predictor of asymmetrical lower extremity loading 6 mos after surgery

Whole body vibration of different frequencies inhibits H-reflex but does not affect voluntary activation

This study aimed to investigate the effects of whole-body vibration (WBV) at a frequency spectrum from 20 to 50 Hz on the Hoffmann (H) reflex and the voluntary motor output of ankle plantar-flexor muscles. A single-group (n: 8), repeated measures design was adopted with four conditions: standing (no vibration), 20, 35 and 50 Hz, each lasting one minute. H-reflex of the soleus muscle, maximal voluntary contraction (MVC) and central activation ratio (CAR) of the plantar-flexors were evaluated before, 1 and 5 min after each frequency condition. H-reflex decreased by 36.7% at 20 Hz, by 28% at 35 Hz, and by 34.8% at 50 Hz after one minute from WBV compared to baseline. Neither MVC nor CAR changed after WBV at all frequency conditions. The short-term, acute inhibition of the H-reflex after WBV at 20, 35 and 50 Hz suggested that decreased excitability of spinal motoneurons is not frequency dependent. On the other hand, the lack of vibration induced effects on MVC and CAR indicated that a 1-min WBV stimulus is not sufficient to affect the voluntary motor output

Effects of resistance training on jumping performance in pre-adolescent rhythmic gymnasts: a randomized controlled study

The aim of this study was to determine the effectiveness of two different resistance training programs on lower limb explosive and reactive strength in young female athletes. Fifty seven rhythmic gymnasts were randomly assigned to unspecific resistance training with dumbbells (12 repetition maximum squats) (n=19; age=12.0±1.8 years) or to specific resistance training with weighted belts (6% of body mass; n=18; age=11.9 ± 1.0 years). Squat jump test, counter movement jump test, hopping test, flexibility of the hip, and anthropometric measures were assessed before and after six weeks training. The main result was that both unspecific resistance training and specific resistance training protocols positively affected the jumping performance, with an increase of the lower limb explosive strength of 6-7%, with no side effects. Counter movement jump flight time increased significantly (p&lt;0.01) while hopping test ground contact time significantly decreased (p&lt;0.01). No significant differences were detected among groups for flexibility, body mass, calf and thigh circumferences. Therefore, six weeks of resistance training that integrates different elements of rhythmic gymnastics training enhance jumping ability in young female athletes