Biomechanics of Skeletal Muscle and Electroymography n Biomechanics of skeletal muscle -Readings: Hamill pp 76-81, n Electromyography -Readings: Hamill pp 81-85; Cram pp 32-37, Ch 3; DeLuca website tutorial ( ),

Muscle structure

The motor unit

Factors Influencing Production of Muscular Tension n Motor unit size n Muscle Fiber Type -Selective recruitment of fiber types: SO FOG FG n Length - tension relationship n Force-velocity relationship

Muscle Fiber Types

Recruitment proceeds from smallest fibers to largest (the size principle)

Three- component model of muscle contraction

Length- tension relationship

Force- Velocity relationship

Electromyography: The analysis of muscle electrical activity n The electromyogram n Recording the Electromyogram n Factors affecting electromyogram n Analyzing the electromyogram n Applications of electromyography

The EMG signal

Recording the electromyogram n Electrodes – -Size -Number -Placement n Signal conduction – wires or telemetry? n Signal conditioning -Amplification -Filtering -Analog to digital conversion -Integration -Frequency analysis

Filtering: Effect of different cutoff frequencies on EMG

Factors affecting the electromyogram

Analyzing the EMG signal

The concept of Frequency decomposition

Converting EMG from time domain to frequency domain What is the time block, Or window over which Frequency analysis is done?

EMG in the Frequency Domain

Applications of electromyography n Timing of excitation n Degree of excitation -Normalization procedures n Muscle force-emg relationship n Muscle fatigue n Clinical gait analysis n Ergonomics n Limitations of EMG

Timing and degree of excitation

EMG-force relationship

Electromechanical delay

Windowing is a critical step in converting EMG signal from time to frequency domain

The fatigue index From EMG – Review the Assumptions Inherent in this procedure

Website article reading assignment n Go to website: and download tutorial article on “surface electromyography detection and recording” n Be prepared to answer the following questions: -What is differential amplification? -What is common mode rejection ratio? -Where should electrodes be placed? -Where should electrodes not be placed? -How large should electrodes be? -Name 3 applications of EMG signal

Further readings on Electromyography Journal articles with specific review assignments: Hildenbrand & Noble. (2004) J Ath Trng. Abdominal muscle activity using different exercise equipment. Caterisano, et al (2002) J Str & Cond Res. EMG of Hip and thigh muscles during back squat. Anders (2006) ACE FitnessMatters. EMG of gluteus maximus during various hip extension exercises. Additional detailed tutorial on methodology (optional): Electromyography in biomechanics. J Appl Biomech, 19: (can be found DeLuca, C. J. (1997) “The use of surface electromyography in biomechanics” on delsys.com website). Click on “library”, then “tutorials”, then article title.delsys.com website