Accepted Manuscript
Type: Regular Article

Title: Lower leg vascular conductance in triathletes

Authors:
Hayate Namatame1, Hirokatsu Tayama2, Seiji Maeda3,4, Takeshi Otsuki2*

Affiliation (s):1Graduate School of Comprehensive Human Sciences, University of Tsukuba, Ibaraki, Japan,
1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577, Japan

2

Faculty of Sport and Health Sciences, Ryutsu Keizai University, Ryugasaki, Ibaraki, Japan,
120 Ryugasaki, Ibaraki 301-8555, Japan

3

Faculty of Health and Sport Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki
305-8577, Japan

4

Faculty of Sport Sciences, Waseda University, 2-579-15 Mikajima, Saitama 359-1192, Japan

Mailing address: otsuki-takeshi@rku.ac.jp

Number of Figures: 3

Number of Tables: 3

Running Title: Vascular conductance in triathletesPage 1

1
2

Abstract
Triathlon is an endurance sport that requires a high aerobic capacity. Previous

3

studies demonstrated that lower-leg vascular conductance (VC) was associated with maximal

4

oxygen uptake. However, it is unclear whether muscular VC is greater in triathletes versus

5

untrained individuals. To test our hypothesis that VC in skeletal muscle is greater in triathletes

6

relative to untrained peers and is associated with higher aerobic capacity in triathletes, this7

study investigated 10 male triathletes (21±1 years of age) and 8 untrained men (22±1 years).

8

Triathletes exhibited greater maximal oxygen uptake than their untrained counterparts (61±69vs. 39±6 mL/kg/min, P < 0.01), as well as lower heart rate (54±7 vs. 65±9 bpm, P < 0.01) and10

body fat (11±2 vs. 16±6 %, P = 0.03). There were no detectable intergroup differences in11systolic (115±8 vs. 117±9 mmHg, P = 0.74), mean (83±6 vs. 86±8 mmHg, P = 0.30), or

12

diastolic (62±6 vs. 65±7 mmHg, P = 0.49) blood pressure. Lower-leg blood flow (4.2±1.3 vs.

13

2.5±0.9 mL/dL/min, P = 0.01) and VC (0.05±0.01 vs. 0.03±0.01 mL/dL/min/mmHg, P =140.02) based on venous occlusion plethysmography were greater in triathletes versus untrained

15

men. Maximal oxygen uptake was correlated with lower-leg blood flow (r = 0.70, P < 0.01)

16

and VC (r = 0.69, P < 0.01). These results demonstrate that lower-leg VC is higher in17

triathletes than in untrained individuals, and it may be associated with higher aerobic capacity

18

in triathletes relative to untrained counterparts.

19
20

Keywords: blood flow; maximal oxygen uptake; vascular resistancePage 221

トライアスロン選手の下腿血管コンダクタンス

22
23
24
25

生田目颯 1，田山寛豪 2，前田清司 3,4，大槻毅 2
1

筑波大学大学院人間総合科学学術院，2 流通経済大学 スポーツ健康科学部
3

筑波大学体育系，4 早稲田大学スポーツ科学部

26
27

トライアスロンは高い有酸素性能力を必要とする持久系スポーツである．先行研究

28

では，下腿の血管コンダクタンス（vascular conductance, VC）は最大酸素摂取量と関

29

連することが示されている．しかしながら，トライアスロン選手において骨格筋の

30

VC が非鍛錬者に比べて大きいか否かは不明である．本研究では，骨格筋の VC は非

31

鍛錬者に比べてトライアスロン選手で大きく，トライアスロン選手の高い有酸素性32

能力と関連しているという仮説を検証するために，男性トライアスロン選手 10 人

33

（21±1 歳）および非鍛錬者 8 人（22±1 歳）を対象に測定を行った．トライアスロン

34

選手は，非鍛錬者よりも最大酸素摂取量（61±6 vs 39±6 mL/kg/min, P < 0.01）は多35

く，心拍数（54±7 vs 65±9 bpm, P < 0.01）および体脂肪率（11±2 vs 16±6 %, P =360.03）は低かった．収縮期血圧（115±8 vs 117±9 mmHg, P = 0.74），平均血圧（83±6 vs37

86±8 mmHg, P = 0.30），拡張期血圧（62±6 vs 65±7 mmHg, P = 0.49）に両者間の有意38差は認められなかった．静脈閉塞プレチスモグラフィで測定した下腿の血流量

39（4.2±1.3 vs 2.5±0.9 mL/dL/min, P = 0.01）および VC（0.05±0.01 vs 0.03±0.01

40mL/dL/min/mmHg, P = 0.02）は，トライアスロン選手で非鍛錬者より高値を示した．

41

最大酸素摂取量と下肢の血流量（r = 0.70, P < 0.01）および VC（r = 0.69, P < 0.01）42との間に相関関係が認められた．これらの結果は，下腿 VC は非鍛錬者よりもトラ

43

イアスロン選手で大きいことを示唆する．トライアスロン選手の下腿 VC は非鍛錬44者に比べて有酸素性能力が高いことに関連するかもしれない．

Page 345

Introduction

46

Triathlon, which consists of swimming, biking, and running, is an endurance sport that47

requires high aerobic capacity1). Since maximal oxygen uptake, the gold standard for48

evaluating aerobic capacity, is strongly correlated with maximal cardiac output, blood

49

circulation plays a crucial role in aerobic capacity2). The main components of the circulatory

50

system are the heart and blood vessels. Whereas many previous studies have investigated51

cardiac function in triathletes3), vascular function in this population has not been fully

52

elucidated.

53
54

Vascular conductance (VC) in skeletal muscle may contribute to aerobic capacity

55

since the peak VC in the lower leg after calf exercise is correlated with maximal oxygen

56

uptake 4-6). However, it is unclear whether muscular VC is greater in triathletes than in

57

untrained individuals. First, triathlon requires both aerobic capacity and muscular strength.

58

Previous studies have demonstrated that triathletes have excellent aerobic capacity7). On the other59

hand, Etxebarria et al.8) reported that cycling of triathlon requires high power output; power output per

60

body weight during cycling of elite-level triathlon race was similar to those of hill climbers. Therefore,

61

triathletes are supposed to be adapted to both endurance and strength training. Capillary density

62

increases with endurance training but not with strength training9). Second, previous studies

63

reported that while systemic vascular resistance (VR, the inverse of VC) was comparable in64

triathletes and their sedentary counterparts10), pulmonary VR was higher in triathletes11). Thus

65

it has been unclear if muscular VC is greater in triathletes relative to untrained individuals. To

66

test our hypothesis that VC in skeletal muscle is greater in triathletes versus untrained

67

individuals and is associated with higher aerobic capacity in triathletes, we investigated68

lower-leg VC and maximal oxygen uptake in male triathletes and their untrained counterparts.

69
70

Methods

Page 4

71

Participants

72

Study participants comprised 10 male triathletes (triathlon career, 7±5 years) in university

73

triathlon clubs and 8 healthy male university students who did not regularly exercise.

74

Inclusion criteria of triathletes were intercollegiate triathletes belonging to triathlon teams

75

with at least 1 year of triathlon career and with training frequency of 5 or more days per week.

76

Five of them had satisfied the entry standards for the Japan Triathlon Championships (i.e.,

77

listed in the top 40 of NTT Japan Cup Ranking or met the qualifying standard [04:38.30 for

78

swimming of 400 m and 09:40.92 for running of 3 km]). Inclusion criteria of untrained men

79

were university students who had sedentary lifestyles (no regular physical activity except for

80

sport classes in a university or high school) for at least 3 years. All were non-smokers, took no

81

medications, and had no chronic diseases. The participants refrained from alcohol

82

consumption and high-intensity exercise on the day before testing, and avoided caffeine

83

consumption on the day of the study. Additionally, they did not eat or drink anything except

84

for water for 2 hours prior to the measurements. After at least 10-minute of rest in the supine

85

position in the air-conditioned laboratory, femoral-ankle pulse wave velocity (PWV) and86

brachial and post-tibial arterial blood pressure were measured simultaneously. Next, lower-leg

87

blood flow (BF) was measured in the supine position. The resting data of vascular

88

measurements were considered as acceptable if resting of the participants were kept during

89

the rest and measurement periods. Finally, a maximal exercise test was performed to measure90

maximal oxygen uptake.

91
92

This study conformed to the principles of the Declaration of Helsinki and was

93

approved by the Ethics Committee of the Ryutsu Keizai University (approval number 25). All

94

participants provided written informed consent prior to study participation.

95
96

Page 597

Lower-leg BF and VC measurements

98

Lower-leg BF and VC were measured using venous occlusion plethysmography with a99

mercury-filled strain gauge (EC6; Hokanson, Bellevue, WA, USA)12). A strain gauge was100

attached to the widest part of the lower leg. Briefly, an ankle cuff was inflated to 50 mmHg

101

above post-tibial arterial systolic blood pressure (SBP) at 1 min before BF measurements

102

began. A femoral cuff was rapidly inflated to 40–50 mmHg for 7 s during a 15-s cycle (E20;103

Hokanson). BF was calculated as the percent change in lower-leg volume during the104

occlusion phase. VC was calculated as BF divided by post-tibial arterial mean blood pressure

105(MBP).

106
107

Maximal oxygen uptake and body fat measurements

108

After the participants underwent a voluntary warm-up (e.g., muscular stretching), a maximal

109

exercise test (4 min at 100 W, with a 30-W increase every 2 min) was conducted using a cycle

110

ergometer (75XL; Konami Sports, Tokyo, Japan). Breath-by-breath oxygen uptake and carbon

111

dioxide production (AE300S; Minato Medical Science, Osaka, Japan), heart rate (HR)112

calculated using 3-lead electrocardiography (LRR-03; GMS, Tokyo, Japan), and rating of113

perceived exertion (RPE, Borg’s 6–20 scale) were measured during the exercise test. We

114

considered a participant as having achieved maximal exertion when at least 2 of the following

115

4 criteria were met; 1) a plateau in oxygen uptake with increasing exercise intensity (<100116mL/min); 2) achievement of age-predicted maximal HR (±10 bpm); 3) a respiratory exchange

117

ratio of at least 1.15; and 4) an RPE of at least 18 units13,14).

118
119

To demonstrate that the participants in this study were well-trained triathletes,

120

body fat was measured using a body impedance–based body composition analyzer (InBody

121

430; InBody, Seoul, South Korea).

122

Page 6

123

Femoral-ankle PWV and blood pressure measurements

124

Femoral-ankle PWV, an index of leg arterial stiffness, was measured using applanation

125

tonometry and air plethysmography. Femoral and post-tibial artery pulse waves were obtained

126

using a pulse wave analyzer (BP-203RPE II; Fukuda Colin, Tokyo, Japan). Pulse wave transit

127

time, the delay between the proximal and distal waveforms, was automatically determined by128

the device. The distance between the femoral and post-tibial recording sites was assessed over129

the surface of the body, and PWV was calculated as the distance divided by the transit time.

130

Simultaneously, SBP, MBP, and diastolic blood pressures (DBP) were measured in the131brachial and post-tibial arteries using oscillometry (BP-203RPE II; Fukuda Colin). HR was

132

calculated using electrocardiography (BP-203RPE II; Fukuda Colin).

133
134

Statistical Analysis

135

Statistical analyses were performed using Statistical Package for Social Sciences (SPSS) for

136

Windows 27 (IBM, Armonk, NY, USA). Values are presented as means ± SDs. Normal

137

distribution of variables was evaluated with the Shapiro-Wilk test. The unpaired t test was

138

used for comparisons between the 2 groups. Relationships between 2 variables were139

investigated using Pearson’s correlation coefficient. P-values < 0.05 were considered140

statistically significant.

141
142

Results

143

All variables were distributed normally. There were no significant intergroup differences in

144age, height, or body weight (Table 1). Compared to their untrained counterparts, triathletes

145

demonstrated significantly lower body fat (Table 1) and HR (Table 2) and significantly greater

146

lower-leg BF based on venous occlusion plethysmography (Figure 1) and maximal oxygen

147

uptake (Figure 2). There were no detectable intergroup differences in blood pressure and148

femoral-ankle PWV (Table 2). Compared to untrained individuals, triathletes had significantlyPage 7

149

greater lower-leg VC (Figure 3).

150
151
152

Maximal oxygen uptake was correlated with body fat, HR, and lower-leg BF and
VC based on venous occlusion plethysmography (Table 3).

153
154

Discussion

155This study measured lower-leg VC based on venous occlusion plethysmography, maximal

156

oxygen uptake, and other indices in male triathletes and age-matched untrained men.

157

Compared to their untrained counterparts, triathletes demonstrated significantly lower body158

fat and HR, and significantly greater lower-leg VC and maximal oxygen uptake. Additionally,159

lower-leg VC was correlated with maximal oxygen uptake. The results demonstrate that160

lower-leg VC is greater in triathletes than in untrained individuals, and it may be associated161with higher aerobic capacity in triathletes relative to untrained peers.

162
163

Lower-leg VC based on venous occlusion plethysmography was higher in164

triathletes versus untrained men in this study. This result is inconsistent with previous studies

165

investigating systemic and pulmonary VR (the inverse of VC) in triathletes. Lakin et al.10)166reported that there was no difference in systemic VR between triathletes and sedentary

167

individuals. However, it is possible that there are differences between systemic and peripheral

168

vascular adaptations to exercise, since systemic VR transiently decreased after swimming

169

while forearm VR increased12). Domenech-Ximenos et al.11) demonstrated that pulmonary VR

170

was higher in triathletes compared to sedentary peers. Again, the discrepancy between the171

study of Domenech-Ximenos et al.11) and our own is not surprising because there are172significant differences between the systemic and pulmonary circulations (e.g., blood pressure173

and roles in oxygen delivery). The inconsistencies between this and previous studies10,11) do

174

not cast doubt on the conclusions of this study.

Page 8175
176

It is apparent that the skeletal muscles of the lower leg play an important role in177

the bike and run portions of triathlon. In particular, the soleus is the largest muscle of the178

triceps surae15) and contributes to upward and forward center-of-mass acceleration during

179

running more than other skeletal muscles16). Regarding biking, electromyography showed that180

the activity of the soleus increased with increasing workload17). We measured VC in the lower

181

leg because previous studies showed that the peak value of lower-leg VC after calf exercise

182

was correlated with maximal oxygen uptake during running4,6) and pedaling exercise5). This183

was a cross-sectional study, but it is possible that the correlation between lower-leg VC based184

on venous occlusion plethysmography and maximal oxygen uptake implies that high VC in

185

triathletes contributes to their significant aerobic capacity.

186
187

In swimmers18), cyclists18,19), runners4,6), and endurance athletes (sport event was188

not described)5), there were no significant differences in resting lower-leg VC or VR between

189

athletes and sedentary individuals. On the other hand, Hepple et al.4) demonstrated that lower-190

leg VC at rest was greater in body builders versus sedentary individuals, runners, and power

191

athletes, and they speculated that high-repetition and high-intensity resistance exercise

192

training in body builders may be implicated in vascular adaptations. High-repetition and

193

intensive resistance exercise is also required in the triathlon during swimming and also during

194

biking, especially on ascending slopes, just after sharp corners, and while increasing speed8).

195

However, not only triathletes but also swimmers swim, and cyclists also do biking. The point

196

makes triathlon unique is conjunction of these exercises and running. Eccentric muscle

197

contractions of lower leg are involved in running whereas concentric contractions are

198

dominant in cycling and swimming20). Kano et al.21) reported that eccentric gastrocnemius

199

muscle contractions increased capillary luminal area in the muscles. Combination of high-200

repetition and intensive resistance exercise during swimming and biking and eccentric muscle

Page 9201

contractions during running may be associated with greater VC in triathletes.

202
203

Resting HR was lower in triathletes versus sedentary men. Generally, endurance-

204

trained athletes with lower resting HR have eccentrically remodeled left ventricle and higher

205

stroke volume22). Additionally, previous studies demonstrated eccentric remodeling of left

206

ventricle in triathletes11,23,24). We can speculate that triathletes in this study also had

207

eccentrically remodeled heart and higher stroke volume. Greater stroke volume increases

208

maximal oxygen uptake in endurance-trained athletes2). It is not surprising that resting HR

209

was correlated with maximal oxygen uptake in this study.

210
211

According to the two-element Windkessel model, VC and arterial stiffness are the212

major vessel factors affecting hemodynamics. VC is mainly determined by internal diameter213

of peripheral arteries, and higher VC indicates superior blood transport capability. Arterial214

stiffness is an inverse of distensibility of arterial wall and associated with ability to buffer

215

fluctuations of blood pressure and flow. Therefore, we measured not only lower-leg VC but

216

also femoral-ankle PWV, an index of leg arterial stiffness. However, there was no detectable

217

difference in femoral-ankle PWV between triathletes and sedentary counterparts. Previous

218

studies on femoral arterial stiffness in runners and swimmers25) and cyclists26) reported219

conflicting results. The result of this study is consistent with the study of Nualnim et al.25) that220

there were no significant differences in femoral arterial stiffness among runners, swimmers,

221

and sedentary peers. Leg artery is a muscular artery with less compliant walls; contribution to222

blood flow and pressure is greater in VC versus arterial stiffness in peripheral muscular

223

arteries. Adaptation of leg arterial stiffness may be non-essential for triathletes.

224
225
226

This study demonstrated that triathletes have greater lower-leg VC based on
venous occlusion plethysmography and that the higher VC is associated with higher aerobic

Page 10227

capacity. The lower-leg VC could be used as an index of conditioning of triathletes and to228

discover a talented triathlete. A decrease in VC with aging increases blood pressure. Again,229

aerobic capacity is a predictor of cardiovascular events27). Investigating vascular adaptations

230

to triathlon could potentially demonstrate the beneficial effects of triathlon as a lifelong sport.

231
232

This study has several limitations. First, this was a cross-sectional study with a233

small sample size. Second, we did not investigate the mechanisms underlying the greater VC

234

in triathletes. Third, we demonstrated that VC is correlated with maximal oxygen uptake but

235

did not conduct multivariate analysis due to small sample size. It is difficult to ascertain

236

whether the correlation between VC and maximal oxygen uptake suggests a causal

237

relationship. Further studies are warranted to establish the effects of triathlon on vascular238

function.

239
240

Conclusions

241

Triathletes have higher VC of the lower leg compared to untrained individuals, and it may be

242

associated with higher aerobic capacity relative to untrained counterparts.

Page 11

Conflict of interests
None.

Author contributions
HN and TO conceived, designed, and performed the experiments; HN analyzed data, prepared
figures, and drafted the manuscript; HT, SM, and TO revised the manuscript; and all authors
approved the final version of the manuscript.

Funding
This research was supported by JSPS KAKENHI (23K10638) and a grant from Advanced
Research Initiative for Human High Performance (ARIHHP), University of Tsukuba.

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Page 15

Table 1. Characteristics of participants.
Triathletes

Untrained

108Age, years

20.7 ± 1.3

21.5 ± 1.1

0.17

Height, cm

169 ± 6171 ± 50.49

Weight, kg

63.3 ± 7.6

64.2 ± 8.9

0.82

Body fat, %11.4 ± 2.1

16.2 ± 6.0

0.03

n

Values are means ± SDs.

P valuePage 16

Table 2. Blood pressure, heart rate, and arterial stiffness.
Triathletes

Untrained

P value

SBP, mmHg

115 ± 8117 ± 90.74

MBP, mmHg

83 ± 686 ± 80.30

DBP, mmHg

62 ± 665 ± 7

0.49

SBP, mmHg

133 ± 10131 ± 120.74

MBP, mmHg

87 ± 686 ± 90.77

DBP, mmHg

66 ± 667 ± 80.91

Heart rate, bpm

54 ± 765 ± 90.01

Femoral-ankle PWV, m/s

7.9 ± 0.9

7.6 ± 0.7

0.47

Brachial

Post-tibial

Values are means ± SDs. SBP, systolic blood pressure; MBP, mean bloodpressure; DBP, diastolic blood pressure; and PWV, pulse wave velocity.

Page 17

Table 3. Correlation with maximal oxygen uptake.
Maximal oxygen uptaker

P value

Body fat- 0.530.02

Heart rate

- 0.56

0.01

Lower-leg BF

0.70< 0.01

Lower-leg VC

0.69< 0.01

BF, blood flow and VC, vascular conductance.

Page 18

Figure Legends
Figure 1. Lower-leg blood flow (BF) in male triathletes and untrained men.
Values are means ± SDs.
Figure 2. Aerobic capacity in male triathletes and untrained men.
Values are means ± SDs.
Figure 3. Lower-leg vascular conductance (VC) in male triathletes and untrained men.
Values are means ± SDs.

Figure 1(Namatame et al.)(mL/dL/min)

Lower-leg BF

6

P = 0.01

5
4
3
2
1
0

Triathlon

ControlFigure 2(Namatame et al.)Maximal oxygen uptake(mL/kg/min)

P < 0.01

70
60
50
40
30

Triathlon Control

Figure 3(Namatame et al.)(mL/dL/min/mmHg)

Lower-leg VC

0.07

P = 0.02

0.06
0.05
0.04
0.03
0.02
0.01

Triathlon Control