Trunk Muscular Endurance Testing
I must emphasise that assessing muscle endurance associated with a reduced chance
of back problems is best done by more than just the Side Bridge Endurance Test.
Ideally you would assess flexor and extensor endurance also and these tests are
preformed in the Kin 343 and 342 courses.
For the purposes of Kin143 we will have every “able
bodied” student only perform the side bridge tests due
to the limited lab time we have. But by all means
conduct the flexor and extensor te sts yourself and
include these scores in your course project !

Protocols for these tests are on the power - point slides
accessible via the Kin143 Web page.
Data from Stuart McGill (a Canadian researcher from McGill University) provides
suggested ratios in the table below. This is because absolute endurance is probably
secondary to the relationship between muscle groups as it is thought muscle imbalances
are a primary cause of back problems. For example, McGill points out that often people
with low back problems have relative weaker extensor strength relative to their flexor
strength (rather than actually having weaker muscles).
Mean Endurance Times (seconds) and Ratios
RSB = Right Side Bridge
LSB = Left Side Bridge
SD = Standard Deviation
Men
Women
Mean
SD
Mean
SD
Extension
161
61
185
60
Flexion
136
66
134
81
RSB
95
32
75
32
LSB
99
37
78
32
Ratios Normalized to the Extensor Endurance Test
Flexion/ Extension Ratio
0.84
0.72
RSB/LSB ratio
0.96
0.96
RSB /Extension Ratio
0.58
0.40
LSB / Extension Ratio
0.61
0.42
Task
All
Mean
173
134
83
86
0.77
0.96
0.48
0.50
Table adapted from: Stuart McGill. Low Back Disorders: Evidence-Based
Prevention and Rehabilitation. Champaign, IL: Human Kinetics, 2002.
SD
62
76
33
36
Interpreting Endurance Scores from the Four Back Tests
(Extension, Endurance, RSB and LSB)
Obviously if you are far from the norms shown above in any of the four tests then this
may be cause for concern. Normal distribution would predict that if you are below one
standard deviation in these tests (e.g. below 100 seconds for males in the extensor test)
then you are in the bottom 16% of the population (conversely a score of 262 seconds or
above puts you in the top 16%). However, care must be taken as people with higher
body weight may tend to score lower (note that females have higher endurance scores
than males in extension).
For the mean values you would simply decide if your score was “Above Mean”,
“At Mean”, or “Below Mean”.
As stated McGill argues that interpreting absolute endurance is probably secondary to
the relationship among the three muscle groups (flexors, lateral, and extensors). He
suggests the following limits on discrepancies between the endurance scores. Scores
outside these limits suggest unbalanced endurance.
Right-Side Bridge / Left Side Bridge Endurance Ratio ≤0.05
McGill suggests the RSB/LSB ratio should not differ from unity (1) by more than 0.05
(i.e. the ratio should be between 0.95 and 1.05).
Mathematically this is written: 0.95 ≤ RSB/LSB Ratio ≤ 1.05.
Outside of these values the muscle balance is UNACCEPTABLE (within values
ACCEPTABLE). So when evaluating your RSB/LSB ratio you should refer to these
suggested values rather than the mean ratio shown in the table above.
Flexion / Extension Endurance Ratio ≤1.0
Therefore if this ratio gives a result less than or equal to 1.0 it is ACCEPTABLE; a ratio
greater than 1.0 is UNACCEPTABLE. Notice that the mean ratio is 0.84 for males and
0.72 for females so do not use these values to decide whether the result is acceptable or
not.
Side Bridge (either side) / Extension Endurance Ratio ≤0.75
Therefore if this ratio gives a result less than or equal to 0.75 it is ACCEPTABLE; a ratio
greater than 0.75 is UNACCEPTABLE. Notice that the mean ratio is around 0.60 for
males (depending on side) and 0.41 for females (depending on side) so again do not
use these values to decide whether the result is acceptable or not..
Despite an obvious and warranted focus on muscles crossing the pelvis, there is no
doubt that a short and weak pectoralis muscles can cause a hunched posture and lead
to back pain. For this reason, overall flexibility (adequate range of motion) is still a
desirable goal as are overall muscular strength and endurance.
Assessment during the acute phase of back pain is obviously not going to be helpful. But
exercise itself can help most back problems (approximately 95%, see KIN 143 lecture
notes), so there is no need for subjects to be completely free of pain before testing.