EMG Chapter 6- inverse relationship- as one goes up the other goes down-
negative correlation or relationship, as one goes up the other
also, lack of sd reported in overground simulation paper.
Hubbard - one of the first to measure EMG activity of the muscle- 1939.
Methodology- types of electrodes:
easiest to use
good for large muscle groups
movement artifact a problem-
motion between skin and muscle
attenuation of signal due to fat
Largest density of neuromuscular junctions
Largest twitch for the least amount of stimulus (current)
Distal muscle belly
Longitudinal versus transverse to muscle fibers
Interelectrode distance- distance between electrodes.
Fine wire electrodes:
Position and depth of insertion.
More difficult to standardize.
EMG analysis methods
Raw emg characteristics
Full wave= absolute value
Half wave = half of the signal only
Low pass filter to keep the lower frequencies- shows general trend of the EMG
Integrate- area under the curve for single or multiple contractions
Integrating over time periods
Integrating to a voltage- the more signal the faster it resets.
Review of methods-
You can use this to look up articles of interest This just lists the general
characteristics of the muscle groups they are about to discuss.
Review of muscles of the lower extremity? Overhead of the muscles
give a list of the attachments
Gluteus maximus- iliac crest, sacrum iliotibial tract of fascia latae, gluteal
tuberosity of femur
Tensor Fasciae latae iliac crest tibia- iliotibial tract
Adductors pubis linea aspera of femur (inside of
rectus femoris ant sup iliac spine upper border of patella
VL greater trochanter femur tib tuberosity through patellar
VM linea aspera of femur same
VI ant femur same
biceps femoris ischial tuberosity head of fibula, lat cond of
semitend " medial surface of tibia
semimenb " medial condyle of tibia
Tibialis Anterior lateral condyle of tibia first metatarsal , first
gastrocnemius lateral and medial condyle of
the femur calcaneus by way of tendon
soleus head of fibula, and medial tibia calcaneus by way of tendon
Phasic action of Individual Muscles- Using a combination of overground and treadmill data
speed closest to 3.8 m/s
active in late swing (at higher speeds)- and continues through first 1/3 of stance
acting eccentrically to slow down the leg and then concentrically to extend
Tensor Fasciae Lata-
antero- medial- primarily hip flexors- active toe-off to midswing. Inactive at heel
strike. which is good due to their hip flexor activity. otherwise get co-contraction
postero- lateral- hip internal rotators and abductors- active just prior to and after
footstrike- GM externally rotates the leg and PL internally rotates it.
Abductors- active in late swing and early stance.- authors did not differentiate. So why is it
anterior fibers -interior rotation,
posterior fibers- external rotation.
Adductors- continuous activity to stabilize pelvis.
biceps femoris- laterally
early swing- no hamstring- knee flexion due to slowing of thigh. Active last 25-40%
late swing- acting to slow down the thigh eccentrically
footstrike- quads and hamstrings active to stabilize leg.
stance- first half it is active
toe-off- max levels here and at toe- off
active during last half of swing (conc) and first part of stance (eccen, greatest activity). RF
to flex hip. VM and VL to stabilize knee.
Often max activity during transition between knee flexion and extension but quiet during
knee extension. Paradox which is tested later.
max activity at heel strike (eccen) to lower foot to the ground ( to protect foot I guess).
Then concentrically to bring foot forward during dorsi flexion.
Shin splints from eccen contraction and decreasing tibial accel?
Gastrocnemius and soleus.
Active from late swing through 50-80% of stance phase.
late swing- active to stabilize the foot with TA then eccentrically to deccelerate the lower
concentric for plantar flexion.
during support- might be like snow boarding discussion where the gastroc is sort of out of
it due to knee flexion but soleus kicks in.
but for faster actions of running then the gastroc comes in for a more ballistic action. maybe
at slower speeds it is just the soleus, and through a smaller range.
Changes in EMG with running speed.
•duration of signal is inversely proportional to running speed.
•In relative terms the muscles are active for a longer percent of the time during the gait
•active earlier in the cycle
•hamstrings come in earlier to slow down the leg
•VM and VL (quads) had a burst during late swing (eccen)
•RF becomes larger during early swing at faster speeds.
Stretch shortening cycle-
eccentric contractions prior to concentric contractions.
pre-load increases the force out put ( legnth- tension curve, and stretch reflex)
gastroc- dorsi flex- then plantar
gluts- eccen last part of hip flexion, then conc for extension
The Authors analysis and experiment-
Figure 6.5 B
Do you understand it?
FS at 1- then stretches until 5 then concentric until toe off- EMG activity increases up until
the point it becomes concentric.
Extensor Paradox Experiment-
foot switch to measure foot impact
goniometer- to measure angles directly
EMG- 500 Hz
high pass filter of 75 Hz keeps everything above 75 Hz of signal.
quad activity stops just before extension. so mainly to slow descent after landing. not for
hip extension may be causing the knee to extend rather than conc quad contraction.
only the gastroc seems to go to Toe - off time. Many experimenters have found that quads
and hamstrings do not continue through toe-off.
last part of a jump is definitely the gastroc for plantar flexion.
May also be that they lose the GM due to skin and FAT resistance.
Summary of Authors doing work
Brandell, 1973 overground
Elliot and Blanksby, 1979 treadmill
Mann and Hagy 1980a overground
Pare et al., 1981 walking jogging (treadmill or overground?)
Schwab et al. 1983 treadmill and overground
MacIntyre and Robertson, 1987 treadmill
Nilsson et al. ?
General findings of the EMG article on walking?