Blood Flow Response To A Single Contraction

During dynamic exercise skeletal muscle blood flow is tightly coupled to the level of muscle activity. However, the factors influencing the blood flow response to a single muscle contraction have not been thoroughly investigated.

PURPOSE

This study examined the blood flow response to a single contraction when tension and contraction time were manipulated. The hypothesis was that the blood flow response to contraction is determined solely by the tension-time index (isometric analog of work).

METHODS

Nine healthy volunteers performed a series of single handgrip isometric contractions. Contractions were performed in duplicate at 15, 30, and 60% of maximal voluntary contraction (MVC) at durations of 0.5, 1, and 2s. Brachial artery diameter and blood velocity were determined beat by beat with Doppler ultrasound (GE Vingmed) using a 10-MHz probe. Forearm blood flow (FBF) was calculated as the product of the resting brachial artery diameter and the mean brachial artery blood velocity.

RESULTS

Peak FBF responded in a graded fashion to graded increases in peak tension with contraction time held constant (35, 56, 90 ml/min for 15, 30, and 60% MVC for 1s). When tension was kept constant, peak FBF responded in a graded fashion to graded increases in duration (77, 90, 97 ml/min for 60% MVC for 0.5, 1, and 2 s). When contraction time was adjusted to maintain a constant tension-time index, peak FBF responded in a graded fashion to graded increases in peak tension (48, 56, 77 ml/min for 15% MVC/2s, 30% MVC/1s, and 60% MVC/0.5s).

CONCLUSION

As expected, there was an increased blood flow associated with a greater tension-time index. Blood flow increased regardless of whether the change in tension-time index was accomplished by an increase in tension or duration of contraction. However, with a constant tension-time index the change in blood flow was related to the peak tension developed. The relationship between the blood flow response and peak tension may be the result of enhanced motor unit recruitment. Supported by NHLBI, VA, and NSERC