Memorial University of Newfoundland

School of Human Kinetics and Recreation

HKR 3310: Exercise Physiology Lab 7

Stretching

 

  1. A subject sits on the bench with the padded belt from the strain gauge attached to the ankle. EMG electrodes are attached to the quadriceps. The lab instructor proceeds to elicit a knee tendon jerk reflex. Record the EMG activity from the reflex action. Observe any time differences in onset of EMG activity and production of force. Why is there EMG activity if there is no initial signal from the brain or evoked electrical stimulation? Explain the mechanisms underlying the knee tendon jerk reflex.

 

 

Reflex force of leg extensors = 68 Newtons

Electromechanical Delay (time from end of reflex activity to start of contraction) = 21 ms


  1. A subject lies on the table with their hip flexed and knee straight. Electrodes are placed on the hamstrings. A partner helps the subject to passively stretch the hamstrings. Measure the integrated EMG activity comparing the relaxed position to the stretched position. Was there an increase in EMG activity? From the stretched position, the subject contracts the quadriceps. Was there any reciprocal inhibition present? Explain the concept of reciprocal inhibition and why or why not it was evident.

 

8
 

8
 
8

Leg movement (hip flexion) to static stretch position begins at 2.8 seconds (first arrow)

Static stretch of hamstrings begins at 6.3 seconds (second arrow).           

 

8
 

8
 

 

Static stretch begins at 4.5 seconds (first arrow).

Antagonist contraction of quadriceps begins at 7.0 seconds (second arrow).
3. A subject performs MVC of the leg extensors. Measure the force, EMG activity of the quadriceps and time to maximal force. Next use static and proprioceptive neuromuscular facilitation stretching techniques to stretch the quadriceps. Perform 3 repetitions of 30 sec each of :

 

a) PNF hip extension

b) standing knee flexion

c) prone assisted knee flexion

 

Have the subject again perform a MVC with EMG activity measured. Are there any significant changes in force or EMG activity? Why might these changes occur? What application would these findings have on sport preparation?

 

Pre-stretch MVC and EMG

MVC leg extension force          = 1052.6 Newtons

Quadriceps EMG amplitude      = 6.6 millivolts

 

 

Post-stretch (stretching of the quadriceps) MVC and EMG

MVC leg extension force          = 797.5 Newtons

Quadriceps EMG amplitude      = 3.9 millivolts