Arm cycling increases short-latency reflex from ankle dorsiflexor afferents to knee extensor muscles

Low-intensity electrical stimulation of the common peroneal nerve (CPN) evokes a short latency reflex in the heteronymous knee extensor muscles (referred to as CPN-reflex). The CPN-reflex is facilitated at a heel strike during walking, contributing to body weight support. However, the origin of the CPN-reflex increase during walking remains unclear. We speculate that this increase originates from multiple sources due to a body of evidence suggesting the presence of neural coupling between the arms and legs. Therefore, we investigated the extent to which the CPN-reflex is modulated during rhythmic arm cycling. Twenty-eight subjects sat in an armchair and were asked to perform arm cycling at a moderate cadence using a stationary ergometer while performing isometric contraction of the knee extensors, such that the CPN-reflex was evoked. CPN-reflex was evoked by stimulating the CPN (0.9-2.0 × the motor threshold [MT] in the tibialis anterior muscle) at the level of the neck of the fibula. The CPN-reflex amplitude was measured from the vastus lateralis (VL). The biphasic reflex response in the VL was evoked within 27-45 ms following CPN stimulation. The amplitude of the CPN-reflex increased during arm cycling compared with that before cycling. The modulation of the CPN-reflex during arm cycling was detected only for CPN stimulation intensity around 1.2 × MT. Furthermore, CPN-reflex modulation was not observed during the isometric contraction of the arm or passive arm cycling. Our results suggest the presence of neural coupling between the CPN-reflex pathways and neural systems generating locomotive arm movement.

Spinal contribution to neuromuscular recovery differs between elbow-flexor and knee-extensor muscles after a maximal sustained fatiguing task

By comparing the changes in motoneuron excitability in elbow-flexor and knee-extensor muscles after sustained fatiguing maximal voluntary contractions, this study shows that motoneuron recovery behavior depends on the muscle performing the exercise. A different recovery pattern in motoneuron excitability occurs in elbow flexors as it recovered by 60 s whereas knee extensors were unaffected by fatigue. This finding can help to increase understanding of the effect of a fatigue and subsequent recovery on neural processes.

No Relationship Between Preoperative and Early Postoperative Strength After ACL Reconstruction

Context: All rehabilitative programs before anterior cruciate ligament (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 preoperatively enhancing quadriceps strength has some beneficial effect on postoperative strength, mainly during the first period. Objective: To determine whether there is any relationship between preoperative 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, and at 60 and 90 days after surgery. Main Outcome Measures: The limb symmetry index (LSI) was quantified for maximal voluntary isometric contraction of the knee extensor muscles and of the knee flexor muscles at 90° joint angle. A 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 < .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 preoperative and postoperative values. Therefore, it appears that there is no need to delay surgery in order to increase the preoperative quadriceps strength before surgery.