Muscular Strength
Maximal amount of force that can be
generated by a specific muscle or
muscle group in a single contraction
(1RM)
Important component of fitness
Reasons to Test Strength
1. Predict Performance
– can predict what sport you are most suited
for (ie., Thorstenssen Test)
2. Implement a training program
– pre-training values training re-
evaluate training etc...
Muscular Strength
3. Measure of rehabilitation
– measure strength pre-season injury
during season use pre-season value as
a guideline for rehab (“back to 100% of
pre-season value”)
4. Identify Muscle Imbalance
– muscle imbalance may lead to injury
– hamstring to quadricep ratio .65-.75
Ways to Measure Strength
1. Isometric - muscle action when
tension is produced but there is no
change in the length of the muscle
– ie., hand grip dynamometer
– Is work being done? (FxD)
– no distance but physiological work is being
done since we are using ATP
Isometric Testing
Advantages
– simple
– cheap
– saves time
Isometric Testing
Disadvantages
– specific to the joint angle (doesn’t reflect
the full ROM)
– doesn’t correlate with sports performance
– more likely to perform the Valsalva
Maneuver
Ways to Measure Strength
2. Isotonic
– muscle action in which a muscle shortens
or lengthens with varying tension and
velocity while overcoming a constant
resistance throughout a ROM
– ie., bench press
Isotonic
Advantages
– correlates better with sports performance
– relatively inexpensive
– accessible
– psychologically seeing work done
Isotonic
Disadvantage
– measuring the weakest point in the ROM
– doesn’t measure strength at different
speeds
Ways to Measure Strength
3. Isokinetically
– maximal tension is developed at all joint
angles throughout the ROM with speed
being constant (have accommodating
resistance at a controlled speed of
movement
Isokinetic
Advantages
– measure strongest point in ROM
– measure strength at different speeds
Isokinetic
Disadvantages
– expensive (40-80K)
– not readily accessible
– need someone knowledgeable to run the
equipment
What Affects Strength?
1. Training Status/size of muscle fibers
2. Type of muscle action
3. Velocity
4. Joint Angle (muscle length)
5. Fiber type
6. #Activated Motor Unit
What Affects Strength?
7. #Fibers within an activated motor
unit
8. Frequency of Impulses
9. Fatigue
Training Status
300
Torque (Nm)
250
A
200
B
150
100
30 90 150 210 270 330 390
Velocity
Types of Muscle Actions
Static - no change in length
Concentric - muscle shortening
Eccentric - muscle lengthening
TYPES OF MUSCLE ACTION
Muscle Action vs. Velocity
325
Torque (Nm)
275
225 CON
175 ECC
125
75
30 90 150 210 270 330 390
Velocity
MUSCLE LENGTH vs FORCE
PRODUCTION
Slow-Twitch (ST) Muscle Fibers
w High aerobic (oxidative) capacity and fatigue resistance
w Low anaerobic (glycolytic) capacity and motor unit
strength
w Slow contractile speed (110 ms) and myosin ATPase
w 10–180 fibers per motor neuron
w Low sarcoplasmic reticulum development
Fast-Twitch (FTa) Muscle Fibers
w Moderate aerobic (oxidative) capacity and fatigue
resistance
w High anaerobic (glycolytic) capacity and motor unit
strength
w Fast contractile speed (50 ms) and myosin ATPase
w 300–800 fibers per motor neuron
w High sarcoplasmic reticulum development
Did You Know…?
The difference in force development between FT and ST
motor units is due to the number of muscle fibers per motor
unit, not the force generated by each fiber.
What Determines Fiber Type?
w Genetics determine which motor neurons innervate our
individual muscle fibers.
w Muscle fibers become specialized according to the type of
neuron that stimulates them.
w Endurance training and muscular inactivity may result in
small changes in the percentage of FT and ST fibers.
w Aging may result in changes in the percentage of FT to ST
fibers.
Frequency of Impulses
w
The rate of action potentials going to a
muscle fiber (Hz)
-force increases with the frequency of
impulses
Fatigue
w The more fatigue the less strength.
w Is fatigue peripheral or central?
Muscular Strength Tests
1. Handgrip Dynamometer
– static
Muscular Strength Tests
2. 1RM
– Protocol
• 1. Have subject complete 5-10 reps at 40-60%
of perceived 1RM
• 2. 1 minute of stretching
• 3. 3-5 reps at 60-80% of perceived 1RM
• 4. Add small amount of weight - attempt
• 5. If successful, rest 3-5 minutes and add more
weight - attempt
1RM
Protocol
• 6. Continue “titrating” until subject is
unsuccessful
• 7. 1RM should be determined within 3-5
maximal efforts
• 8. 1RM = the weight of the last successfully
completed lift
Estimation of 1RM (submaximal)
Submaximally estimate 1RM
– Advantage – don’t have to do max testing
and not as likely to injure your athletes.
Epley Equation
1RM = (((0.033*Reps) Rep Wt.) + Rep
Wt.)
Muscular Strength Tests
3. Isokinetic Dynamometers
– leg extension strength at various velocities
(velocity spectrum testing)
– 3 maximal muscle actions at each velocity
– record the highest value of the three
Ways to Express Results
1. Absolute
2. Relative to BW
3. Relative to FFW
Muscular Endurance
Ability of a muscle group to execute
repeated contractions over a period of
time sufficient to cause muscular
fatigue, or to maintain a specific
percentage of MVC for a prolonged
period of time
Muscular Endurance
1. Grip Endurance
2. Sit-ups
3. Push-ups
4. Thorstensson
Grip Endurance
1. Squeeze dynamometer for 1 minute
maximally - record initial strength and
final strength
2. Squeeze dynamometer at a
submaximal percent of MVC (ie., 60%)
to fatigue
Sit-ups
Supine
Knees at 90º
Arms at side
Fingers reaching for masking tape 8-12
cm from resting
Metronome - 40 beats/min
Push-ups
Males in “up” position
Females in “knee” position
Hands shoulder width apart
Chin touches mat
As many as possible consecutively and
without rest
Thorstensson
Endurance test that allows for the
calculation of %FT
50 Reps
180 º/sec
Thorstensson
%Decline = ((Initial PT - Final PT) ÷
Initial PT ) x 100
%FT = (% Decline - 5.2) ÷ 0.9
Muscular Endurance
400
300
Torque
A
200
B
100
0
1 5 10 20 30 40 50
Repetitions