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Brachial artery blood flow during submaximal isometric contraction of the biceps brachii and triceps brachii in humans: A preliminary observation
Journal of Bodywork & Movement Therapies (2013) 17, 165e168
Available online at www.sciencedirect.com
journal homepage: www.elsevier.com/jbmt
MUSCLE PHYSIOLOGY
Brachial artery blood flow during submaximal isometric contraction of the biceps brachii and triceps brachii in humans: A preliminary observation Giulia Ledro, PT a, Andrea Turrina, PT b, Alessandro Picelli, MD a,c, Carla Stecco, MD d, Francesco Principe, MD e, Carlo Cacciatori, MD e, Nicola Smania, MD a,f,* a Neuromotor and Cognitive Rehabilitation Research Centre, Department of Neurological, Neuropsychological, Morphological and Movement Sciences, University of Verona, P.le L.A. Scuro, 10, 37134 Verona, Italy b Madrid School of Osteopathy, Italian Section, Verona, Italy c University of Rome ‘‘La Sapienza’’, Rome, Italy d Section of Anatomy, Department of Human Anatomy and Physiology, University of Padua, Padua, Italy e Institute of Radiology, University of Verona, Verona, Italy f Neurological Rehabilitation Unit, G.B. Rossi University Hospital, Verona, Italy
Received 16 April 2012; received in revised form 20 July 2012; accepted 25 July 2012
KEYWORDS Brachial artery; Brachial fascia; Blood flow velocity; Diameter; Muscle contraction
Summary The purpose of this study was to evaluate brachial artery blood flow changes during submaximal isometric contraction of the biceps and triceps brachii, in order to clarify the influence of the upper arm muscles activity on the local arterial flow. The brachial artery blood flow velocity and diameter were evaluated in twenty healthy men (mean age 29.6 years) at baseline (resting position) and during submaximal isometric contraction of the biceps and triceps brachii by means of ultrasonography (B-MODE and Doppler ultrasound methods). The brachial artery blood flow velocity was significantly higher than resting position during submaximal isometric contraction of the biceps (P < 0.001) and triceps brachii (P Z 0.019). As to the
* Corresponding author. Neuromotor and Cognitive Rehabilitation Research Center, Department of Neurological, Neuropsychological, Morphological and Movement Sciences, University of Verona, P.le L.A. Scuro, 10, 37134 Verona, Italy. Tel.: þ39 45 8124573; fax: þ39 45 8124495. E-mail address: [email protected] (N. Smania). 1360-8592/$ - see front matter ª 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jbmt.2012.07.014
166
G. Ledro et al. brachial artery diameter, no significant change was observed during submaximal isometric contractions of the biceps and triceps brachii. Our preliminary findings suggest that the brachial artery blood flow velocity similarly increases during submaximal isometric contraction of the biceps and triceps brachii. ª 2012 Elsevier Ltd. All rights reserved.
Introduction The brachial artery is the major blood vessel of the upper arm. It commences at the lower margin of the tendon of the teres major, continuing from the axillary artery (Stranding, 2008). Just below the lower border of the teres major, a deep branch of the brachial artery, called profunda brachii artery, arises from its posterolateral part (Stranding, 2008). Initially, the brachial artery lies medial to the humerus, gradually running in front of the bone as it goes down the arm. At the bend of the elbow, the brachial artery lies midway between the epicondyles, and then divides into the radial and ulnar arteries (Stranding, 2008). Previous studies in humans have observed changes in the brachial artery blood flow during static handgrip exercises (Kagaya and Homma, 1997). In addition, modifications in the profunda brachii artery blood flow have been reported during sustained submaximal isometric contraction of the triceps brachii (Griffin et al., 2001). Despite the need to better understand the connections between the major anatomic structures of the arm, to the best of our knowledge, no previous study has evaluated brachial artery blood flow during isometric contraction of the main upper arm muscles. In line with the fundamental role of the brachial artery in upper arm circulation (Stranding, 2008; Kagaya and Homma, 1997; Griffin et al., 2001), and in order to clarify the influence of upper arm muscles activity on local arterial flow, we carried out this preliminary investigation aimed at evaluating changes of the brachial artery blood flow during submaximal isometric contraction of the biceps brachii and triceps brachii in humans.
Materials and methods Healthy, right-handed, adult men between 20 and 35 years of age qualified for inclusion. Exclusion criteria were: assumption of nicotine, caffeine or alcohol <48 h before evaluation; previous orthopaedic conditions (such as traumatic injuries or fractures) involving the right arm. All participants were volunteers and gave their written informed consent for participation in the study. The protocol was carried out according to the Declaration of Helsinki and was approved by the local Ethics Committee. During evaluation subjects were seated on a chair with their right shoulder in 90 of flexion, the elbow positioned at a 90 angle and the forearm in front of them with the palm facing inward (Griffin et al., 2001). The wrist was placed in a metal cuff mounted on a force transducer that measured elbow flexion and extension forces (JR3 transducer, Woodland, CA). Four maximal voluntary contractions (two elbow flexions and two elbow extensions) were performed: the larger flexion and extension torques were used to calculate the 20% maximal voluntary contraction forces
(Griffin et al., 2001). Following baseline evaluation (resting position), each subject performed a 5 s sustained isometric biceps brachii contraction of 20% maximal voluntary contraction (a visual target of the maximal voluntary contraction force was presented on a screen in front of the subject). With the same modality, after 10 min the subject performed a 5 s sustained isometric triceps brachii contraction of 20% maximal voluntary contraction. These procedures were repeated for five consecutive days (one evaluation per day). Measurements of mean blood flow velocity and diameter were made from the brachial artery in the antecubital fossa region of the right arm in the resting position and during submaximal isometric contractions of the biceps brachii and triceps brachii (Griffin et al., 2001). Ultrasound Doppler and B-MODE methods (Sequoia 512, Siemens, Erlangen, Germany) were used. Normality in data distribution was verified by the ShapiroeWilk test. The paired t test or the Wilcoxon signed ranks test were performed (according to the normality in data distribution) to compare outcome measures mean values as follows: between resting position e biceps brachii isometric contraction, resting position e triceps brachii isometric contraction and biceps brachii isometric contraction e triceps brachii isometric contraction. The alpha level for significance was set at P < 0.05. Statistical analysis was carried out using the SPSS for Windows statistical package, version 20.0.
Results Twenty adult healthy men (mean age: 29.6 2.5 years; mean resting heart rate: 68 4 bpm; mean resting systolic pressure: 116 4 mmHg; mean resting diastolic pressure: 70 3 mmHg; mean submaximal voluntary contraction of the biceps brachii: 66.1 7.8 N; mean submaximal voluntary contraction of the triceps brachii: 48.4 7.3 N) were recruited from 29 volunteers of the Verona University School of Medicine during the period from May to October 2011. The ShapiroeWilk test verified that our data was not normally distributed. Thus, we performed statistical analysis by means of the Wilcoxon signed ranks test. Statistically significant changes in the brachial artery blood flow velocity were found in regards to the resting position e biceps brachii isometric contraction comparison (P < 0.001; Z Z 3.823) and resting position e triceps brachii isometric contraction comparison (P Z 0.019; Z Z 2.352) but not in the biceps brachii isometric contraction e triceps brachii isometric contraction comparison (P Z 0.100; Z Z 1.643). No statistically significant changes in the brachial artery diameter were found in regards to all comparisons. Raw data (means and standard deviations) about resting position, biceps brachii and triceps brachii contraction evaluations are reported in Table 1.
Brachial artery blood flow during submaximal isometric contraction of the biceps brachii and triceps brachii Table 1
167
Raw data and comparisons.
Outcome measures Brachial artery
Baseline Mean (SD)
BB contraction Mean (SD)
TB contraction Mean (SD)
Comparisons Baseline BB contraction P value (Z )
Baseline TB contraction P value (Z )
BB contraction TB contraction P value (Z )
Blood flow velocity (m/s) Diameter (cm)
0.116 (0.03)
0.192 (0.06)
0.140 (0.05)
<0.001 (3.823)*
0.019 (2.352)*
0.100 (1.643)
0.338 (0.04)
0.348 (0.06)
0.341 (0.05)
0.145 (1.457)
0.970 (2.352)
0.494 (0.684)
Abbreviations: SD, Standard Deviation; BB, Biceps brachii; TB, Triceps brachii; m/s, metres/seconds; cm, centimetres. * Z Statistically significant (P < 0.05).
Discussion The aim of this study was to evaluate modifications of the brachial artery blood flow during submaximal isometric contraction of the biceps brachii and triceps brachii in healthy humans. Our results showed that the brachial artery blood flow velocity significantly increases during isometric contraction of the biceps brachii and triceps brachii. On the other hand, a difference that did not reach statistical significance was found in the brachial artery blood flow velocity between isometric contractions of the biceps brachii versus triceps brachii. No statistically significant change of the brachial artery diameter was observed during isometric contractions of the biceps brachii and triceps brachii compared to the resting position. In humans, the brachial artery mainly provides the biceps brachii arterial supply (Stranding, 2008; Shoemaker et al., 1997; Kanbayashi et al., 1993), while the profunda brachii artery supplies the triceps brachii (Stranding, 2008; Griffin et al., 2001). On this basis, our findings regarding blood flow through the brachial artery supplying the biceps brachii during submaximal isometric contraction are consistent with that of Griffin et al. (2001), in which the profunda brachii artery blood flow velocity significantly increased during submaximal isometric contraction of the triceps brachii without changes of the artery diameter. A challenging question now is to understand why the blood flow velocity through the brachial artery similarly increased not only during the submaximal isometric contraction of the supplied biceps brachii but also during the submaximal isometric contraction of its antagonist muscle (namely, the triceps brachii). The more plausible explanation for our results may be found when considering that the profunda brachii artery, which supplies the triceps brachii, is a deep branch of the brachial artery (Stranding, 2008). Consequently, the increase of brachial artery blood flow velocity during biceps brachii and triceps brachii contraction can be interpreted as a response to the contractile activity and metabolic needing of both muscles (Hamann et al., 2005). Furthermore, in submaximal isometric muscle contraction, the blood flow response represents a balance between metabolically induced vasodilatation, vessel compression by the contracting muscles and increased perfusion pressure (Kagaya and Homma, 1997). Thus, the local release of vasoactive metabolites and endothelial relaxation factors, blood
pressure variations, passive alterations in flow and the sympathetic outflow have to be considered to further interpret our findings (Shoemaker et al., 1997; Kagaya et al., 2010). Finally, in order to explain our results, we would like to also consider the anatomy of the brachial artery, which is covered, in the front, by the brachial fascia (see Fig. 1) (Stranding, 2008). This fascial structure continues with the latissimus dorsi fascia that has strong connections with the triceps fascia (Stecco et al., 2007, 2009). In literature a myofascial force transmission occurring between antagonistic muscles has been described (Huijing and Baan, 2008; Huijing et al., 2007). On this basis, we might hypothesize that the brachial artery blood flow would change not only in response to the muscular activity but also as a consequence of the fascial mechanic action on the vascular girdle. Moreover, a previous study by Hocking and colleagues, reported interesting evidence about the role of fascial connections between muscle and capillary flow (Hocking et al., 2008). In particular, the Authors suggested that tensile forces from actively contracting skeletal muscles alter the conformation of fibronectin fibrils surrounding the vascular wall and transiently expose matricryptic sites that, in turn, initiate a biochemical signal leading to a change in arteriolar diameter. This would be a mechanism of converting a mechanical signal into a biomechanical response (Hocking et al., 2008).
Figure 1
Fascial connections of the brachial artery.
168 This study was a preliminary observation with several limitations and it is important to point out that the strength of our conclusions is very limited. First, the sample size was small. Taking into account a previous study about blood flow modifications during submaximal isometric muscle contraction (Griffin et al., 2001), we estimate that 44 subjects would provide 90% power to detect a significant difference in the blood flow velocity of the brachial artery between the different conditions examined in this study. Second, we investigated an extremely healthy population, as shown by the low variability of both diastolic and systolic measurements obtained at baseline. Third, we took into account only two parameters regarding the brachial artery (namely, blood flow velocity and diameter). Finally, we did not evaluate other arteries such as the profunda brachii or the axillary arteries. It is plausible that the population size and the number of parameters considered may have hindered the evaluation of some aspects involving the brachial artery.
Conclusions Our preliminary findings suggest that the brachial artery blood flow velocity similarly increases during submaximal isometric contraction of the biceps brachii and triceps brachii in humans. In order to further validate our observations, studies on a larger and more diversified population considering more vessels and more vascular parameters are needed. Future studies should also take into account the role of the arterial plexus around the shoulder. Doppler studies including impedance measures of arm circulation could be useful in order to evaluate not only the arterial supply to the triceps through the arterial anastomoses around the scapula but also the blood flow needed during biceps and triceps exercise.
Conflict of interest/Financial disclosures No commercial party having a direct financial interest in the results of the research supporting this manuscript has or will confer a benefit on the authors or on any organization with which the authors are associated.
G. Ledro et al.
References Griffin, L., Garland, S.J., Ivanova, T., Hughson, R.L., 2001. Blood flow in the triceps brachii muscle in humans during sustained submaximal isometric contractions. European Journal of Applied Physiology 84, 432e437. Hamann, J.J., Kluess, H.A., Buckwalter, J.B., Clifford, P.S., 2005. Blood flow response to muscle contractions is more closely related to metabolic rate than contractile work. Journal of Applied Physiology 98, 2096e2100. Hocking, D.C., Titus, P.A., Sumagin, R., Sarelius, I.H., 2008. Extracellular matrix fibronectin mechanically couples skeletal muscle contraction with local vasodilation. Circulation Research 102, 372e379. Huijing, P.A., Baan, G.C., 2008. Myofascial force transmission via extramuscular pathways occurs between antagonistic muscles. Cells Tissues Organs 188, 400e414. Huijing, P.A., van de Langenberg, R.W., Meesters, J.J., Baan, G.C., 2007. Extramuscular myofascial force transmission also occurs between synergistic muscles and antagonistic muscles. Journal of Electromyography and Kinesiology 17, 680e689. Kagaya, A., Homma, S., 1997. Brachial arterial blood flow during static handgrip exercise of short duration at varying intensities studied by a Doppler ultrasoundmethod. Acta Physiologica Scandinavica 160, 257e265. Kagaya, A., Ohmori, F., Okuyama, S., Muraoka, Y., Sato, K., 2010. Blood flow and arterial vessel diameter change during graded handgrip exercise in dominant and non-dominant forearms of tennis players. Advances in Experimental Medicine and Biology 662, 365e370. Kanbayashi, T., Takafuji, T., Sato, Y., 1993. On the arterial supply in the human biceps brachii muscle. Okajimas Folia Anatomica Japonica 69, 289e310. Shoemaker, J.K., MacDonald, M.J., Hughson, R.L., 1997. Time course of brachial artery diameter responses to rhythmic handgrip exercise in humans. Cardiovascular Research 35, 125e131. Stecco, A., Macchi, V., Stecco, C., Porzionato, A., Ann Day, J., Delmas, V., De Caro, R., 2009. Anatomical study of myofascial continuity in the anterior region of the upper limb. Journal of Bodywork and Movement Therapies 13, 53e62. Stecco, C., Gagey, O., Macchi, V., Porzionato, A., De Caro, R., Aldegheri, R., Delmas, V., 2007. Tendinous muscular insertions onto the deep fascia of the upper limb. First part: anatomical study. Morphologie 91, 29e37. Stranding, S., 2008. Gray’s Anatomy: The Anatomical Basis of Clinical Practice. Churchill Livingstone, London.
Available online at www.sciencedirect.com
journal homepage: www.elsevier.com/jbmt
MUSCLE PHYSIOLOGY
Brachial artery blood flow during submaximal isometric contraction of the biceps brachii and triceps brachii in humans: A preliminary observation Giulia Ledro, PT a, Andrea Turrina, PT b, Alessandro Picelli, MD a,c, Carla Stecco, MD d, Francesco Principe, MD e, Carlo Cacciatori, MD e, Nicola Smania, MD a,f,* a Neuromotor and Cognitive Rehabilitation Research Centre, Department of Neurological, Neuropsychological, Morphological and Movement Sciences, University of Verona, P.le L.A. Scuro, 10, 37134 Verona, Italy b Madrid School of Osteopathy, Italian Section, Verona, Italy c University of Rome ‘‘La Sapienza’’, Rome, Italy d Section of Anatomy, Department of Human Anatomy and Physiology, University of Padua, Padua, Italy e Institute of Radiology, University of Verona, Verona, Italy f Neurological Rehabilitation Unit, G.B. Rossi University Hospital, Verona, Italy
Received 16 April 2012; received in revised form 20 July 2012; accepted 25 July 2012
KEYWORDS Brachial artery; Brachial fascia; Blood flow velocity; Diameter; Muscle contraction
Summary The purpose of this study was to evaluate brachial artery blood flow changes during submaximal isometric contraction of the biceps and triceps brachii, in order to clarify the influence of the upper arm muscles activity on the local arterial flow. The brachial artery blood flow velocity and diameter were evaluated in twenty healthy men (mean age 29.6 years) at baseline (resting position) and during submaximal isometric contraction of the biceps and triceps brachii by means of ultrasonography (B-MODE and Doppler ultrasound methods). The brachial artery blood flow velocity was significantly higher than resting position during submaximal isometric contraction of the biceps (P < 0.001) and triceps brachii (P Z 0.019). As to the
* Corresponding author. Neuromotor and Cognitive Rehabilitation Research Center, Department of Neurological, Neuropsychological, Morphological and Movement Sciences, University of Verona, P.le L.A. Scuro, 10, 37134 Verona, Italy. Tel.: þ39 45 8124573; fax: þ39 45 8124495. E-mail address: [email protected] (N. Smania). 1360-8592/$ - see front matter ª 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jbmt.2012.07.014
166
G. Ledro et al. brachial artery diameter, no significant change was observed during submaximal isometric contractions of the biceps and triceps brachii. Our preliminary findings suggest that the brachial artery blood flow velocity similarly increases during submaximal isometric contraction of the biceps and triceps brachii. ª 2012 Elsevier Ltd. All rights reserved.
Introduction The brachial artery is the major blood vessel of the upper arm. It commences at the lower margin of the tendon of the teres major, continuing from the axillary artery (Stranding, 2008). Just below the lower border of the teres major, a deep branch of the brachial artery, called profunda brachii artery, arises from its posterolateral part (Stranding, 2008). Initially, the brachial artery lies medial to the humerus, gradually running in front of the bone as it goes down the arm. At the bend of the elbow, the brachial artery lies midway between the epicondyles, and then divides into the radial and ulnar arteries (Stranding, 2008). Previous studies in humans have observed changes in the brachial artery blood flow during static handgrip exercises (Kagaya and Homma, 1997). In addition, modifications in the profunda brachii artery blood flow have been reported during sustained submaximal isometric contraction of the triceps brachii (Griffin et al., 2001). Despite the need to better understand the connections between the major anatomic structures of the arm, to the best of our knowledge, no previous study has evaluated brachial artery blood flow during isometric contraction of the main upper arm muscles. In line with the fundamental role of the brachial artery in upper arm circulation (Stranding, 2008; Kagaya and Homma, 1997; Griffin et al., 2001), and in order to clarify the influence of upper arm muscles activity on local arterial flow, we carried out this preliminary investigation aimed at evaluating changes of the brachial artery blood flow during submaximal isometric contraction of the biceps brachii and triceps brachii in humans.
Materials and methods Healthy, right-handed, adult men between 20 and 35 years of age qualified for inclusion. Exclusion criteria were: assumption of nicotine, caffeine or alcohol <48 h before evaluation; previous orthopaedic conditions (such as traumatic injuries or fractures) involving the right arm. All participants were volunteers and gave their written informed consent for participation in the study. The protocol was carried out according to the Declaration of Helsinki and was approved by the local Ethics Committee. During evaluation subjects were seated on a chair with their right shoulder in 90 of flexion, the elbow positioned at a 90 angle and the forearm in front of them with the palm facing inward (Griffin et al., 2001). The wrist was placed in a metal cuff mounted on a force transducer that measured elbow flexion and extension forces (JR3 transducer, Woodland, CA). Four maximal voluntary contractions (two elbow flexions and two elbow extensions) were performed: the larger flexion and extension torques were used to calculate the 20% maximal voluntary contraction forces
(Griffin et al., 2001). Following baseline evaluation (resting position), each subject performed a 5 s sustained isometric biceps brachii contraction of 20% maximal voluntary contraction (a visual target of the maximal voluntary contraction force was presented on a screen in front of the subject). With the same modality, after 10 min the subject performed a 5 s sustained isometric triceps brachii contraction of 20% maximal voluntary contraction. These procedures were repeated for five consecutive days (one evaluation per day). Measurements of mean blood flow velocity and diameter were made from the brachial artery in the antecubital fossa region of the right arm in the resting position and during submaximal isometric contractions of the biceps brachii and triceps brachii (Griffin et al., 2001). Ultrasound Doppler and B-MODE methods (Sequoia 512, Siemens, Erlangen, Germany) were used. Normality in data distribution was verified by the ShapiroeWilk test. The paired t test or the Wilcoxon signed ranks test were performed (according to the normality in data distribution) to compare outcome measures mean values as follows: between resting position e biceps brachii isometric contraction, resting position e triceps brachii isometric contraction and biceps brachii isometric contraction e triceps brachii isometric contraction. The alpha level for significance was set at P < 0.05. Statistical analysis was carried out using the SPSS for Windows statistical package, version 20.0.
Results Twenty adult healthy men (mean age: 29.6 2.5 years; mean resting heart rate: 68 4 bpm; mean resting systolic pressure: 116 4 mmHg; mean resting diastolic pressure: 70 3 mmHg; mean submaximal voluntary contraction of the biceps brachii: 66.1 7.8 N; mean submaximal voluntary contraction of the triceps brachii: 48.4 7.3 N) were recruited from 29 volunteers of the Verona University School of Medicine during the period from May to October 2011. The ShapiroeWilk test verified that our data was not normally distributed. Thus, we performed statistical analysis by means of the Wilcoxon signed ranks test. Statistically significant changes in the brachial artery blood flow velocity were found in regards to the resting position e biceps brachii isometric contraction comparison (P < 0.001; Z Z 3.823) and resting position e triceps brachii isometric contraction comparison (P Z 0.019; Z Z 2.352) but not in the biceps brachii isometric contraction e triceps brachii isometric contraction comparison (P Z 0.100; Z Z 1.643). No statistically significant changes in the brachial artery diameter were found in regards to all comparisons. Raw data (means and standard deviations) about resting position, biceps brachii and triceps brachii contraction evaluations are reported in Table 1.
Brachial artery blood flow during submaximal isometric contraction of the biceps brachii and triceps brachii Table 1
167
Raw data and comparisons.
Outcome measures Brachial artery
Baseline Mean (SD)
BB contraction Mean (SD)
TB contraction Mean (SD)
Comparisons Baseline BB contraction P value (Z )
Baseline TB contraction P value (Z )
BB contraction TB contraction P value (Z )
Blood flow velocity (m/s) Diameter (cm)
0.116 (0.03)
0.192 (0.06)
0.140 (0.05)
<0.001 (3.823)*
0.019 (2.352)*
0.100 (1.643)
0.338 (0.04)
0.348 (0.06)
0.341 (0.05)
0.145 (1.457)
0.970 (2.352)
0.494 (0.684)
Abbreviations: SD, Standard Deviation; BB, Biceps brachii; TB, Triceps brachii; m/s, metres/seconds; cm, centimetres. * Z Statistically significant (P < 0.05).
Discussion The aim of this study was to evaluate modifications of the brachial artery blood flow during submaximal isometric contraction of the biceps brachii and triceps brachii in healthy humans. Our results showed that the brachial artery blood flow velocity significantly increases during isometric contraction of the biceps brachii and triceps brachii. On the other hand, a difference that did not reach statistical significance was found in the brachial artery blood flow velocity between isometric contractions of the biceps brachii versus triceps brachii. No statistically significant change of the brachial artery diameter was observed during isometric contractions of the biceps brachii and triceps brachii compared to the resting position. In humans, the brachial artery mainly provides the biceps brachii arterial supply (Stranding, 2008; Shoemaker et al., 1997; Kanbayashi et al., 1993), while the profunda brachii artery supplies the triceps brachii (Stranding, 2008; Griffin et al., 2001). On this basis, our findings regarding blood flow through the brachial artery supplying the biceps brachii during submaximal isometric contraction are consistent with that of Griffin et al. (2001), in which the profunda brachii artery blood flow velocity significantly increased during submaximal isometric contraction of the triceps brachii without changes of the artery diameter. A challenging question now is to understand why the blood flow velocity through the brachial artery similarly increased not only during the submaximal isometric contraction of the supplied biceps brachii but also during the submaximal isometric contraction of its antagonist muscle (namely, the triceps brachii). The more plausible explanation for our results may be found when considering that the profunda brachii artery, which supplies the triceps brachii, is a deep branch of the brachial artery (Stranding, 2008). Consequently, the increase of brachial artery blood flow velocity during biceps brachii and triceps brachii contraction can be interpreted as a response to the contractile activity and metabolic needing of both muscles (Hamann et al., 2005). Furthermore, in submaximal isometric muscle contraction, the blood flow response represents a balance between metabolically induced vasodilatation, vessel compression by the contracting muscles and increased perfusion pressure (Kagaya and Homma, 1997). Thus, the local release of vasoactive metabolites and endothelial relaxation factors, blood
pressure variations, passive alterations in flow and the sympathetic outflow have to be considered to further interpret our findings (Shoemaker et al., 1997; Kagaya et al., 2010). Finally, in order to explain our results, we would like to also consider the anatomy of the brachial artery, which is covered, in the front, by the brachial fascia (see Fig. 1) (Stranding, 2008). This fascial structure continues with the latissimus dorsi fascia that has strong connections with the triceps fascia (Stecco et al., 2007, 2009). In literature a myofascial force transmission occurring between antagonistic muscles has been described (Huijing and Baan, 2008; Huijing et al., 2007). On this basis, we might hypothesize that the brachial artery blood flow would change not only in response to the muscular activity but also as a consequence of the fascial mechanic action on the vascular girdle. Moreover, a previous study by Hocking and colleagues, reported interesting evidence about the role of fascial connections between muscle and capillary flow (Hocking et al., 2008). In particular, the Authors suggested that tensile forces from actively contracting skeletal muscles alter the conformation of fibronectin fibrils surrounding the vascular wall and transiently expose matricryptic sites that, in turn, initiate a biochemical signal leading to a change in arteriolar diameter. This would be a mechanism of converting a mechanical signal into a biomechanical response (Hocking et al., 2008).
Figure 1
Fascial connections of the brachial artery.
168 This study was a preliminary observation with several limitations and it is important to point out that the strength of our conclusions is very limited. First, the sample size was small. Taking into account a previous study about blood flow modifications during submaximal isometric muscle contraction (Griffin et al., 2001), we estimate that 44 subjects would provide 90% power to detect a significant difference in the blood flow velocity of the brachial artery between the different conditions examined in this study. Second, we investigated an extremely healthy population, as shown by the low variability of both diastolic and systolic measurements obtained at baseline. Third, we took into account only two parameters regarding the brachial artery (namely, blood flow velocity and diameter). Finally, we did not evaluate other arteries such as the profunda brachii or the axillary arteries. It is plausible that the population size and the number of parameters considered may have hindered the evaluation of some aspects involving the brachial artery.
Conclusions Our preliminary findings suggest that the brachial artery blood flow velocity similarly increases during submaximal isometric contraction of the biceps brachii and triceps brachii in humans. In order to further validate our observations, studies on a larger and more diversified population considering more vessels and more vascular parameters are needed. Future studies should also take into account the role of the arterial plexus around the shoulder. Doppler studies including impedance measures of arm circulation could be useful in order to evaluate not only the arterial supply to the triceps through the arterial anastomoses around the scapula but also the blood flow needed during biceps and triceps exercise.
Conflict of interest/Financial disclosures No commercial party having a direct financial interest in the results of the research supporting this manuscript has or will confer a benefit on the authors or on any organization with which the authors are associated.
G. Ledro et al.
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