The relative contribution of motor unit recruitment and rate coding to the production of static isometric muscle force

Strips of tonically contracted canine tracheal and bronchial airway smooth muscles (AWSM) were studied in vitro to compare dynamic muscle force during stretch-retraction cycles with static isometric muscle force at various length points within the cycling range. At any particular rate, a characteristic force-length loop was obtained by cycling over a given range of lengths. Dynamic muscle force dropped well below static isometric muscle force at lengths short of the peak length at all rates of cycling. When stretch or retraction of the muscle was stopped at any point along either path of the cycle, muscle force rose to approach the isometric force at that length. Dynamic force at the peak length of the cycle remained close to, or slightly greater than, the static isometric force. The results suggest that the velocity of shortening of tonically contracted AWSM is very slow relative to the rates of cycling employed. A slow rate of shortening of AWSM relative to the rate of change in airway caliber during breathing could account for well-known effects of volume history on airway tone.

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Contributions of motor-unit recruitment and rate modulation of compensation for muscle yielding

Journal of Neurophysiology ◽

10.1152/jn.1982.47.5.797 ◽

1982 ◽

Vol 47 (5) ◽

pp. 797-809 ◽

Cited By ~ 13

Author(s):

P. J. Cordo ◽

W. Z. Rymer

Keyword(s):

Motor Unit ◽

Stretch Reflex ◽

Muscle Force ◽

Motor Units ◽

Muscle Stiffness ◽

Motor Unit Recruitment ◽

Reflex Response ◽

Rate Modulation ◽

Stimulus Rate ◽

Wide Range

1. Subdivided portions of the cut ventral root innervation of the soleus muscle were electrically stimulated in 14 anesthetized cats. The stimulus trains imposed on these nerves simulated the recruitment and rate-modulation patterns of single motor units recorded during stretch-reflex responses in decerebrate preparations. Each activation pattern was evaluated for its ability to prevent muscle yield. 2. Three basic stimulus patterns, recruitment, step increases in stimulus rate, and doublets were imposed during the course of ramp stretches applied over a wide range of velocities. The effect of each stimulus pattern on muscle force was compared to the force output recorded without stretch-related recruitment or rate modulation. 3. Motor-unit recruitment was found to be most effective in preventing yield during muscle stretch. Newly recruited motor units showed no evidence of yielding for some 250 ms following activation, at which time muscle stiffness declined slightly. This time-dependent resistance to yield was observed regardless of whether the onset of the neural stimulus closely preceded or followed stretch onset. 4. Step increases in stimulus rate arising shortly after stretch onset did not prevent the occurrence of yield at most stretch velocities, but did augment muscle stiffness later in the stretch. Doublets in the stimulus train were found to augment muscle stiffness only when they occurred in newly recruited motor units. 5. These results suggest that at low or moderate initial forces, the prevention of yield in lengthening, reflexively intact muscle results primarily from rapid motor-unit recruitment. To a lesser extent, the spring-like character of the stretch-reflex response also derives from step increases in firing rate of motor units active before stretch onset and doublets in units recruited during the course of stretch. Smooth rate increases appear to augment muscle force later in the course of the reflex response.

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ISOMETRIC MUSCLE FORCE AS A PREDICTOR OF A MAXIMAL MUSCLE EFFORT IN THE LEG PRESS TEST

sportlogia ◽

10.5550/sgia.191501.en.pkdz ◽

2019 ◽

Vol 15 (1) ◽

pp. 81-89

Author(s):

Borko Petrović ◽

◽

Aleksandar Kukrić ◽

Radenko Dobraš ◽

Nemanja Zlojutro ◽

...

Keyword(s):

Muscle Force ◽

Leg Press ◽

Isometric Muscle ◽

Isometric Muscle Force

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Short Review: Rate Coding Motor Unit Recruitment Patterns

The Journal of Strength and Conditioning Research ◽

10.1519/1533-4287(1989)003<0034:srrcmu>2.3.co;2 ◽

1989 ◽

Vol 3 (2) ◽

pp. 34

Author(s):

Michael Deschenes

Keyword(s):

Motor Unit ◽

Short Review ◽

Motor Unit Recruitment ◽

Rate Coding ◽

Recruitment Patterns

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Hamstring Stiffness Returns More Rapidly After Static Stretching Than Range of Motion, Stretch Tolerance, and Isometric Peak Torque

Journal of Sport Rehabilitation ◽

10.1123/jsr.2017-0203 ◽

2019 ◽

Vol 28 (4) ◽

pp. 325-331 ◽

Cited By ~ 8

Author(s):

Genki Hatano ◽

Shigeyuki Suzuki ◽

Shingo Matsuo ◽

Satoshi Kataura ◽

Kazuaki Yokoi ◽

...

Keyword(s):

Muscle Strength ◽

Range Of Motion ◽

Muscle Force ◽

Static Stretching ◽

Passive Stiffness ◽

Hamstring Injuries ◽

Isometric Muscle ◽

Torque Angle ◽

Isometric Muscle Force ◽

Rest Intervals

Context: Hamstring injuries are common, and lack of hamstring flexibility may predispose to injury. Static stretching not only increases range of motion (ROM) but also results in reduced muscle strength after stretching. The effects of stretching on the hamstring muscles and the duration of these effects remain unclear. Objective: To determine the effects of static stretching on the hamstrings and the duration of these effects. Design: Randomized crossover study. Setting: University laboratory. Participants: A total of 24 healthy volunteers. Interventions: The torque–angle relationship (ROM, passive torque [PT] at the onset of pain, and passive stiffness) and isometric muscle force using an isokinetic dynamometer were measured. After a 60-minute rest, the ROM of the dynamometer was set at the maximum tolerable intensity; this position was maintained for 300 seconds, while static PT was measured continuously. The torque–angle relationship and isometric muscle force after rest periods of 10, 20, and 30 minutes were remeasured. Main Outcome Measures: Change in static PT during stretching and changes in ROM, PT at the onset of pain, passive stiffness, and isometric muscle force before stretching were compared with 10, 20, and 30 minutes after stretching. Results: Static PT decreased significantly during stretching. Passive stiffness decreased significantly 10 and 20 minutes after stretching, but there was no significant prestretching versus poststretching difference after 30 minutes. PT at the onset of pain and ROM increased significantly after stretching at all rest intervals, while isometric muscle force decreased significantly after all rest intervals. Conclusions: The effect of static stretching on passive stiffness of the hamstrings was not maintained as long as the changes in ROM, stretch tolerance, and isometric muscle force. Therefore, frequent stretching is necessary to improve the viscoelasticity of the muscle–tendon unit. Muscle force decreased for 30 minutes after stretching; this should be considered prior to activities requiring maximal muscle strength.

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