KINE 2200: Biomechanics
Lab 6
The Neuromuscular System
Activity A: The Force-Velocity Relationship
Necessary Equipment:
· Barbell and weights
· GymAware Linear Position Transducer
· Exercise Attire
The maximum force a muscle is capable of producing is dependent on the velocity of
shortening. During concentric contractions, a muscle shortening (contracting) faster
cannot produce as much force and the same muscle if it were contracting slower. This is
called the Force-Velocity Relationship.
1. Attach the strap of the GymAware to the barbell and prepare it for
deadlifts. Begin with a light weight that you can lift very easily. Perform a deadlift
as fast as you can and record the mean velocity measured by the GymAware.
Load more weight on the barbell so the deadlift is moderately difficult and
perform another deadlift as fast as you can and record the velocity. Repeat the
process two more times, increasing the weight each time until it is very difficult to
complete the deadlift.
Rep/Trial Number Force (Barbell Weight) Mean Velocity (m/s)
1 65 0.81
2 85 0.84
3 105 0.62
4
2. Complete the graph by plotting the data you recorded in the previous
section with force on the Y axis and velocity on the X axis.
105 ⑧
85 ⑧
65
·
0.62 0.64 0.66 0.0.68 0.7 0.72 0.74 0.76 0.78 0.8 0.82 0.84 0.86 0.88 0.9
3. How did the velocity change as the weight was increased? Was this what
you expected? Why or why not?
The velocity decreased while the weight increased each trial. Yes, this is what I expected because we
had to use more force as it got heavier.
Activity B: Stretch-Shortening Cycle
Necessary Equipment
· gFlight
The muscle spindles are proprioceptors that detect the stretch of a muscle. When a
muscle is rapidly stretched, the muscle spindles sense the stretch and cause the
muscle to contract. This reflex helps to increase the force production of the subsequent
contraction. To take advantage of the stretch shortening cycle, a rapid stretch must be
immediately followed by a concentric contraction. If the concentric contraction does not
occur immediately after the stretch, the stored energy is lost as heat.
1. Complete three trials of squat jumps and three trials of countermovement
jumps. During the squat jump, you will squat, pause in the squat for 3 seconds,
then jump as high as possible. During the countermovement jump, you will drop
rapidly into your squat and immediately jump as high as possible. Record your
jump heights for each jump condition in the table below.
Jump Condition Trial 1 Trial 2 Height Trial 3 Average
Height Height Height
Squat Jump 34.3 34.4 34.1 34.26
Countermovement 39.8 36.8 39.2 38.6
Jump
2. Which jump condition resulted in the highest average jump height? Is this
what you expected? Why or why not?
The countermovement jump condition was higher than the squat jump condition based on the average
jump heights. We expected the countermovement to be higher than the squat jump because you are
producing more momentum with the countermovement.
Activity C: Proprioceptive Neuromuscular Facilitation (PNF)
Necessary Equipment
· Rehab table
The Golgi Tendon Organ (GTO) and Muscle Spindles are two proprioceptors found in the
tendons and muscles. The GTO senses tension in the musculotendinous unit while muscle
spindles sense the amount and rate of stretch of a muscle. When tension in a muscle increases,
the GTO is stimulated and inhibits the muscle to reduce tension. When a muscle is stretched,
the muscle spindle is stimulated and causes the muscle to contract to slow or prevent the
stretching. Proprioceptive Neuromuscular Facilitation is a stretching technique that specifically
targets the GTOs and muscle spindles, inhibiting them and leading to increased flexibility.
Complete each of the two PNF techniques listed below, one on the right limb and one on the left
limb.
1. Contract-Relax: Have the patient lay supine on the rehab table. The practitioner
will passively flex the patient’s hip until a hamstring stretch is felt. At this point, ask the
patient to actively contract the hamstrings while the practitioner resists the contraction.
Hold the contraction for 5 seconds, then relax. Once the patient relaxes, the practitioner
should be able to flex the hip even further, placing more stretch on the hamstring.
Repeat the process to see if you can further increase range of motion. Have every group
member serve as the patient and practitioner.
2. Agonist-Contract: Have the patient lay supine on the rehab table. The
practitioner will passively flex the patient’s hip until a hamstring stretch is felt. At this
point, ask the patient to actively contract the quadriceps. The practitioner should not
resist the contraction while the patient holds the contraction for 5 seconds, then relax.
Once the patient relaxes, the practitioner should be able to flex the hip even further,
placing more stretch on the hamstring. Repeat the process to see if you can further
increase range of motion. Have every group member serve as the patient and
practitioner.
3. Did it appear that one technique improved flexibility more than the other? If so,
which one?
Yes, the second technique when I was the patient improved the flexibility while my quad was
engaged. When I was a practitioner, my patient was more flexible when her hamstring was engaged.
This is because the muscle spindles sense stretch and Golgi tendon organs sense tension wanting the
muscle to relax. When we contracted the antagonist muscle in the second technique, after a while the
Golgi tendon organs need the leg to relax and when it finally does you get to stretch further and be
more flexible.
Activity D: Fatigue and Muscle Activation
Necessary Equipment
· Laptop with EMG software
· Delsys EMG
· Hand Grip Dynamometer
Muscle force production is partially dependent on the stimuli it receives from the nervous
system. To have a large muscle force output, a large number of motor units must be activated
rapidly. When muscles fatigue, their force producing capacity is diminished. To reach a specific
force output, a certain amount of muscle activation (i.e., more motor units and higher firing
frequency) is required. When a muscle is fatigued, more activation is needed to reach the same
force output.
Place an EMG electrode on an individuals finger flexors on their forearm. Have them squeeze
the handgrip dynamometer to a submaximal force output and maintain that force output through
the duration of the activity. Record the EMG activity for 3 minutes while the participant maintains
the same force output.
1. Review the average amount of muscle activity (RMS) throughout the 3 minutes.
Did muscle activity change throughout this duration? If there were changes, were they as
you expected?
When looking at the muscle activity over the three minutes, it decreased as time went on. I
expected this because the muscle would fatigue.
2. Why do you think this occurred?
When the muscle gets fatigue, it tries to recruit more bigger motor units to produce the
same amount of force that was being produced in the beginning.
