Muscle
Strength
Assessment

Muscular Strength
The ability of a muscle group to develop maximal
contractile force against a resistance in a single
contraction.
Muscular Endurance
The ability of a muscle group to exert submaximal
force for extended time periods.

Concentric
Force exerted by muscle or
muscle group exceeds
external resistance or load
 Joint angle decreases
 Muscle shortens
Eccentric Isometric
Contraction Types
Braking mechanism to
decelerate body segment
movement (resist gravity)
 Joint angle increases
 Muscle lengthens
Force exertion and
external resistance
equal
 Static Joint angle
 Static muscle length

Isometric Contraction
Both concentric and eccentric contractions are sometimes
called isotonic (“iso,” same; “tonic,” tension). The term
“isotonic contraction” is a misnomer because the tension
produced by the muscle group fluctuates greatly even
though the resistance is constant throughout the range of
motion (ROM).

The fluctuation in muscular force
during isotonic contractions is
due to the change in muscle
length and angle of pull as the
bony lever is moved, creating a
strength curve that is unique for
each muscle group.
For example, the strength of the
knee flexors is maximal at 160°
to 170°.
Isometric Contraction

Isokinetic Contraction
 Maximal contraction of muscle or muscle group at a constant
velocity throughout entire range of motion (ROM).
 Specialized machines control velocity of contraction and adjust
external resistance to match the force produced at degree in the
ROM.
 Resistance is variable, velocity is constant)
(Electromechanical devices vary the resistance to match the muscular force produced
at each point in the ROM. Thus, isokinetic exercise machines allow the muscle group to
encounter variable but maximal resistances during the movement.)

Muscle
Strength
Assessment
Tools

Muscle strength is typically
measured isometrically. This
limits variability due to muscle
length (sarcomere size) and
movement ability
Isometric strength = the maximum force exerted in a single contraction
against an immovable resistance (i.e., maximum voluntary isometric
contraction or MVIC)

• Isometric dynamometer
• Measures static grip strength
• Advantages: easy protocol,
portable, inexpensive, common
testing method
• Disadvantage: doesn’t equate well
to performance, limited to 1
movement
Grip Dynamometer

Hand-Held Dynamometer
• Isometric dynamometer
• Measures isometric muscle
strength in a variety of muscle
groups and motions
• Advantages: wide variety of tests
can be done, portable, accurate
data, better mimic common
movements
• Disadvantage: more tester error,
errors due to site placement, more
expensive

Large Frame Dynamometer
• Isometric dynamometer
• Measures isometric muscle
strength in one motion, but at
varying joint angles
• Advantages: very accurate data,
isolates specific joint angles
• Disadvantage: very expensive, not
portable, requires space and user
training

Isokinetic Dynamometer
• Isokinetic dynamometer
• Contriols speed of joint movement
and measures force throughout a
joint range of motion.
• Advantages: very accurate data,
isolates joint angles for better data
• Disadvantage: very expensive, not
portable, requires space and user
training

Dynamic Strength
• One-repetition maximum (1RM):
maximum weight that can be lifted
for one complete repetition of the
movement
• Advantages: Easy of use,
movements are common to many
subjects, comparable data available
• Disadvantages: Trial and error, not
precise data, machines differ

Dynamic Endurance
• Perform multiple reps with weight
that is set submaximal load
(%1RM) or set %body mass.
• The YMCA (Golding 2000) and ACSM
(2010)

Issues with
Muscle
Assessment
Tests

Test/retest reliability is
the biggest issue with
muscle strength
assessment

Test/retest reliability issues