EMG Chapter 6-    inverse relationship- as one goes up the other goes down-

                  negative correlation or relationship, as one goes up the other  

                  goes down.

                  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:

Surface 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)

      Electrode placement-

      Distal muscle belly

      Muscle belly

      Longitudinal versus transverse to muscle fibers

      Skin resistance

      Electrode size

      Interelectrode distance- distance between electrodes.


      Fine wire electrodes:

      Smaller area

      Movement artifact

      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


      Linear envelopes-

            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

                        Origin                  Insertion

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

Gluteus maximus-

      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

the hip.

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.



semimembrinosis- medially

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.

Tibialis Anterior-

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-

6 runners

4 m/s

treadmill running

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?