Download Grip Strength Lab - Illinois State University

ILLINOIS STATE UNIVERSITY
SCHOOL OF KINESIOLOGY AND RECREATION
KNR 342, Occupational Biomechanics
Grip Strength Lab
OBJECTIVES:
1. To demonstrate the changing grip strength in relation to differences in spread of the grip
dynamometer
READINGS: From Chaffin & Andersson , Muscle mechanics section 2.3.5
The length-tension relationship describes the change in the force producing capability of
muscle related to differences in length at the time of activation. For isometric actions, the
difference in force is mainly attributed to differences in overlap of the actin and myosin
myofilaments. Difference may also be attributed to variation in the contribution of the elastic
component of muscle, but the affect during isometric activity is not as great as during dynamic
activity.
The purpose of this lab is to demonstrate some in-vivo applications of the relationship.
Because the actual length of muscle cannot be directly measured in-vivo, and because the
measured output is an externally applied force and not muscle tension, the relationship to be
demonstrated is better referred to as the joint position-grip strength relationship.
In the lab, data will be collected under three scenarios to demonstrate how the measured grip
strength varies according to the joint position at the time of measurement:
1)
Grip width varied. Typically, the grip dynamometer is aligned so that the pressure bar is
aligned with the metacarpal heads (knuckles). In this lab, the pressure bar will be aligned
with 3 different positions: 1) at the distal phalangeal joint of the middle finger; 2) with
the metacarpal head of the middle finger; 3) with the center of the palm. Keep your elbow
straight and wrist in the neutral position. Note: for each position, record the distance
between the grip handle and finger grip.
2) Elbow position varied. Some of the muscles responsible for flexion of the fingers originate
on the medical epicondyle of the humerus. Thus, position of the elbow joint should affect
the measured grip strength. In this lab, four different elbow positions will be used: 1)
elbow straight; 2) elbow at 45º of flexion; 3) elbow at 90º of flexion; 4) elbow at 135º of
flexion. Keep your wrist straight, and dynamometer set at the metacarpal head of the
middle finger.
3) Wrist position varied. The muscles responsible for flexion of the fingers pass through the
carpal tunnel on the anterior portion of the wrist. The alignment of the wrist joint should
thus affect the measured grip strength. In this lab, three different wrist positions will be
used: 1) wrist flexed maximally (bent forward); 2) wrist in the neutral, or anatomical,
position; 3) wrist extended maximally (bent backwards). Keep your elbow straight and
dynamometer set at the metacarpal head of the middle finger. (See Figure 1 below)
Methods
The grip dynamometers are very expensive. Handle them with care--do not drop them or
toss them to each other. Get into groups of four individuals. Each group member will perform all
10 conditions of the grip strength measurement. To reduce learning effects and fatigue
effects, randomize the 10 conditions across all the group members and within each group
member (mix up the order of performance). Complete two trials in each condition (provide rest
between trials). Record the grip strength scores on the data sheet.
Note: when submitting your work, create a cover sheet for the lab. In the top right hand
corner, put your name in bold, upper case letters. In non-bold, lower case letters, list the names
of your group members under your own name.
First, conduct the following analysis of the data:
a. For each grip strength condition, calculate the average grip strength for the group
members (ie sum the grip strengths across the group members and divide by the number of
people)
b. Calculate the average of the three conditions of “neutral wrist, normal grip width, elbow
straight” condition. Use this single value in place of the three individual mean values.
c. Create a bar graph showing the average grip strength in each condition. You should create
separate graphs as follows: Figure 1) grip width; Figure 2) elbow position; and Figure 3)
wrist position.
d. Using the mean value for “neutral wrist, normal grip width, elbow straight” as the baseline
value, calculate the percentage change in grip strength for all the other conditions. Create a
single graph (Figure 4) showing the percentage change in each condition. Write a paragraph
that summarizes the graph.
Second, answer the following questions. Base your explanations on the length-tension
relationship.
1. Explain what happens to the length of the wrist flexor muscles as grip width is altered.
i. Based on the length-tension relationship, what is the expected order of strength,
from highest strength to lowest strength, of the grip spans?
ii. Referring to Figure 1, write a paragraph summarizing the observed effect of grip
width on grip strength. Were these results as expected?
iii. Compare and contrast the mean value of grip strength, and the mean value of each
member of your group, to the data in Figure 2, Effect of grasp span on maximum
isometric grip strength. (part of this lab sheet). (Note: you may need to convert the
strength measures in kg to strength in Newtons; also, express your scores as an
estimated z-score [see the anthro lab for a review of z-score])
iv. Did each member of your group change grip strength to the same extent as the grip
width was altered? Explain why there were individual variations.
2. Explain what happens to the length of the wrist flexor muscles as elbow position is altered.
i. Based on the length-tension relationship, what is the expected order of strength,
from highest strength to lowest strength, of the different elbow positions?
ii. Referring to Figure 2, write a paragraph summarizing the observed effect of elbow
position on grip strength. Were these results as expected?
iii. Did each member of your group change grip strength as elbow position was altered?
Explain why.
3. Explain what happens to the length of the wrist flexor muscles as wrist position is altered.
i. Based on the length-tension relationship, what is the expected order of strength,
from highest strength to lowest strength, of the different wrist positions?
ii. Referring to Figure 3, write a paragraph summarizing the observed effect of wrist
position on grip strength. Were these results as expected?
iii. Did each member of your group change grip strength as wrist position was altered?
Explain why.
4. Referring to the graph created in d. above, summarize the effects of grip span, elbow
position and wrist position on grip strength. Basing your summary on the importance of the
length tension relationship and force production, explain the basis for the relative
differences in the effects of the different conditions.
5. What factors other than the length tension relationship could help explain the outcome of
this lab experience? Explain.
6. To what activities might this lab be relevant?
7. How could this lab be improved??? Be specific.
Figure 1. Wrist positions for grip strength testing.
600
Force (N)
500
400
300
200
100
2.5
3.5
4.5
5.5
6.5
Grasp Span (cm)
Figure 2. Effect of grasp span on maximum isometric grip strength. The dashed curves are one standard deviation on
either side of the mean (solid line).