Sensitivity of muscle proton spin-spin relaxation time as an index of muscle activation

1994 ◽  
Vol 77 (1) ◽  
pp. 84-92 ◽  
Author(s):  
G. Yue ◽  
A. L. Alexander ◽  
D. H. Laidlaw ◽  
A. F. Gmitro ◽  
E. C. Unger ◽  
...  
Keyword(s):  
Relaxation Time ◽  
Spin Relaxation ◽  
Muscle Activation ◽  
Biceps Brachii ◽  
Proton Spin ◽  
Spin Relaxation Time ◽  
Elbow Flexor ◽  
Flexor Muscles ◽  
Elbow Flexor Muscles ◽  
Long Head

The purpose of this study was to determine the minimum number of contractions that are needed to detect an increase in the muscle proton spin-spin relaxation time (T2) at a given exercise intensity. Five healthy human subjects performed five sets of an exercise that included concentric and eccentric contractions of the elbow-flexor muscles with loads that were 25 or 80% of maximum. With the 80% load, the five sets involved 1, 2, 5, 10, or 20 repetitions of the exercise; with the 25% load the five sets were 2, 5, 10, 20, or 40 repetitions. The upper arm of each subject was imaged before and immediately after each set of the exercise. Spin-echo images (repetition time/echo time = 2,000 ms/30, 60, 90, and 120 ms) were collected using an extremity coil, and T2 values were calculated. The signal intensity was measured from the elbow-flexor and -extensor muscles and from the bone marrow of the humerus. With the 80% load, T2 increased in the short head of the biceps brachii after two repetitions of the elbow exercise and after five repetitions in the brachialis and the long head of the biceps brachii. With the 25% load, T2 became longer after five repetitions of the exercise for the short head of the biceps brachii and after 10 repetitions for the brachialis and the long head of the biceps brachii. T2 varied linearly with the number of contraction repetitions for each of the elbow-flexor muscles at either load (r2 > or = 0.97, P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

1093 SENSITIVITY OF MAGNETIC RESONANCE PROTON SPIN-SPIN RELAXATION TIME AS AN INDEX OF MUSCLE ACTIVATION

1994 ◽  
Vol 26 (Supplement) ◽  
pp. S194
Author(s):  
G. Yue ◽  
A. L. Alexander ◽  
D. H. Laidlaw ◽  
A. F. Gmitro ◽  
E. C. Unger ◽  
...  
Keyword(s):  
Relaxation Time ◽  
Magnetic Resonance ◽  
Spin Relaxation ◽  
Muscle Activation ◽  
Proton Spin ◽  
Spin Relaxation Time

Older Adults Use a Unique Strategy to Lift Inertial Loads With the Elbow Flexor Muscles

2000 ◽  
Vol 83 (4) ◽  
pp. 2030-2039 ◽  
Author(s):  
Andrew E. Graves ◽  
Kurt W. Kornatz ◽  
Roger M. Enoka
Keyword(s):  
Young Adults ◽  
Elbow Joint ◽  
Muscle Activation ◽  
Angular Displacement ◽  
Elbow Flexor ◽  
Lengthening Contractions ◽  
Old Adults ◽  
Flexor Muscles ◽  
Elbow Flexor Muscles ◽  
Target Force

The purpose of this study was to determine the effect of age on the ability to exert steady forces and to perform steady flexion movements with the muscles that cross the elbow joint. An isometric task required subjects to exert a steady force to match a target force that was displayed on a monitor. An anisometric task required subjects to raise and lower inertial loads so that the angular displacement around the elbow joint matched a template displayed on a monitor. Steadiness was measured as the coefficient of variation of force and as the normalized standard deviation of wrist acceleration. For the isometric task, steadiness as a function of target force decreased similarly for old adults and young adults. For the anisometric task, steadiness increased as a function of the inertial load and there were significant differences caused by age. Old adults were less steady than young adults during both shortening and lengthening contractions with the lightest loads. Furthermore, old adults were least steady when performing lengthening contractions. These behaviors appear to be associated with the patterns of muscle activation. These results suggest that different neural strategies are used to control isometric and anisometric contractions performed with the elbow flexor muscles and that these strategies do not change in parallel with advancing age.

Proton spin-spin relaxation time of peel and flesh of navel orange varieties exposed to freezing temperature

2005 ◽  
Vol 85 (14) ◽  
pp. 2482-2486 ◽  
Author(s):  
Prem N Gambhir ◽  
Young J Choi ◽  
David C Slaughter ◽  
James F Thompson ◽  
Michael J McCarthy
Keyword(s):  
Relaxation Time ◽  
Spin Relaxation ◽  
Freezing Temperature ◽  
Proton Spin ◽  
Spin Relaxation Time ◽  
Navel Orange

Sex differences in the fatigability of arm muscles depends on absolute force during isometric contractions

2001 ◽  
Vol 91 (6) ◽  
pp. 2686-2694 ◽  
Author(s):  
Sandra K. Hunter ◽  
Roger M. Enoka
Keyword(s):  
Muscle Activation ◽  
Pressor Response ◽  
Voluntary Contraction ◽  
Elbow Flexor ◽  
Endurance Time ◽  
Muscle Activation Patterns ◽  
Flexor Muscles ◽  
Elbow Flexor Muscles ◽  
Target Force ◽  
The Absolute

Women are capable of longer endurance times compared with men for contractions performed at low to moderate intensities. The purpose of the study was 1) to determine the relation between the absolute target force and endurance time for a submaximal isometric contraction and 2) to compare the pressor response and muscle activation patterns of men [26.3 ± 1.1 (SE) yr] and women (27.5 ± 2.3 yr) during a fatiguing contraction performed with the elbow flexor muscles. Maximal voluntary contraction (MVC) force was greater for men (393 ± 23 vs. 177 ± 7 N), which meant that the average target force (20% of MVC) was greater for men (79.7 ± 6.5 vs. 36.7 ± 2.0 N). The endurance time for the fatiguing contractions was 118% longer for women (1,806 ± 239 vs. 829 ± 94 s). The average of the rectified electromyogram (%MVC) for the elbow flexor muscles at exhaustion was similar for men (31 ± 2%) and women (30 ± 2%). In contrast, the heart rate and mean arterial pressure (MAP) were less at exhaustion for women (94 ± 6 vs. 111 ± 7 beats/min and 121 ± 5 vs. 150 ± 6 mmHg, respectively). The target force and change in MAP during the fatiguing contraction were exponentially related to endurance time ( r 2 = 0.68 and r 2 = 0.64, respectively), whereas the change in MAP was linearly related to target force ( r 2 = 0.51). The difference in fatigability of men and women when performing a submaximal contraction was related to the absolute contraction intensity and was limited by mechanisms that were distal to the activation of muscle.

Low-frequency fatigue and neuromuscular performance after exercise-induced damage to elbow flexor muscles

2008 ◽  
Vol 105 (4) ◽  
pp. 1146-1155 ◽  
Author(s):  
James M. Dundon ◽  
John Cirillo ◽  
John G. Semmler
Keyword(s):  
Eccentric Exercise ◽  
Biceps Brachii ◽  
Maximum Voluntary Contraction ◽  
Low Frequency ◽  
Elbow Flexor ◽  
Triceps Brachii ◽  
Force Fluctuations ◽  
Flexor Muscles ◽  
Elbow Flexor Muscles ◽  
Low Frequency Fatigue

The purpose of this study was to quantify the association between low-frequency fatigue (LFF) and the increase in EMG and force fluctuations after eccentric exercise of elbow flexor muscles. Ten subjects performed two tasks involving voluntary isometric contractions of elbow flexors: a maximum voluntary contraction (MVC) and a constant-force task at five submaximal target forces (5, 10, 20, 40, 60% MVC) while EMG was recorded from biceps and triceps brachii. A third task involved electrical stimulation of biceps brachii at 12 frequencies (1–100 Hz). These tasks were performed before, after, and 2 h and 24 h after concentric or eccentric exercise. MVC force declined after eccentric exercise (34% decline) and remained depressed 24 h later (22% decline), whereas the reduced force following concentric exercise (32%) was recovered 2 h later. Biceps brachii EMG and force fluctuations during the submaximal voluntary contractions increased after eccentric exercise (both ∼2× greater) with the greatest effect at low forces. LFF was equivalent immediately after both types of exercise (50–60% reduction in 20:100 Hz force) with a slower recovery following eccentric exercise. A significant association was found between the change in LFF and EMG ( r2values up to 0.52), with the strongest correlations observed at low forces (20% MVC) and at 2 h after exercise. In contrast, there were no significant associations between LFF and force fluctuations during voluntary or electrically evoked contractions, suggesting that other physiological factors located within the muscle are likely to be playing a major role in the impaired motor performance after eccentric exercise.

Eccentric exercise increases EMG amplitude and force fluctuations during submaximal contractions of elbow flexor muscles

2007 ◽  
Vol 103 (3) ◽  
pp. 979-989 ◽  
Author(s):  
John G. Semmler ◽  
Kylie J. Tucker ◽  
Trevor J. Allen ◽  
Uwe Proske
Keyword(s):  
Eccentric Exercise ◽  
Biceps Brachii ◽  
Maximum Voluntary Contraction ◽  
Elbow Flexor ◽  
Twofold Increase ◽  
Force Fluctuations ◽  
Emg Amplitude ◽  
Concentric Exercise ◽  
Flexor Muscles ◽  
Elbow Flexor Muscles

The purpose of this study was to determine the effect of eccentric exercise on the ability to exert steady submaximal forces with muscles that cross the elbow joint. Eight subjects performed two tasks requiring isometric contraction of the right elbow flexors: a maximum voluntary contraction (MVC) and a constant-force task at four submaximal target forces (5, 20, 35, 50% MVC) while electromyography (EMG) was recorded from elbow flexor and extensor muscles. These tasks were performed before, after, and 24 h after a period of eccentric (fatigue and muscle damage) or concentric exercise (fatigue only). MVC force declined after eccentric exercise (45% decline) and remained depressed 24 h later (24%), whereas the reduced force after concentric exercise (22%) fully recovered the following day. EMG amplitude during the submaximal contractions increased in all elbow flexor muscles after eccentric exercise, with the greatest change in the biceps brachii at low forces (3–4 times larger at 5 and 20% MVC) and in the brachialis muscle at moderate forces (2 times larger at 35 and 50% MVC). Eccentric exercise resulted in a twofold increase in coactivation of the triceps brachii muscle during all submaximal contractions. Force fluctuations were larger after eccentric exercise, particularly at low forces (3–4 times larger at 5% MVC, 2 times larger at 50% MVC), with a twofold increase in physiological tremor at 8–12 Hz. These data indicate that eccentric exercise results in impaired motor control and altered neural drive to elbow flexor muscles, particularly at low forces, suggesting altered motor unit activation after eccentric exercise.

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