Clin Physiol Funct Imaging (2015) 35, pp104–109
doi: 10.1111/cpf.12133
Effects of different periods of hypoxic training on glucose metabolism and insulin sensitivity Takuma Morishima1, Yuta Hasegawa1, Hiroto Sasaki1, Toshiyuki Kurihara2, Takafumi Hamaoka2 and Kazushige Goto2 1
Graduate School of Sport and Health Science, Ritsumeikan University, and 2Faculty of Sport and Health Science, Ritsumeikan University, Shiga, Japan
Summary Correspondence Kazushige Goto. Faculty of Sport and Health Science, Ritsumeikan University, 1-1-1, Nojihigashi, Kusatsu, Shiga 525-8577, Japan E-mail: [email protected]
Accepted for publication Received 17 October 2013; accepted 3 January 2014
Key words endurance training; insulin sensitivity; length of training period; normobaric hypoxia; short-term training
This study examined the effects of different periods of hypoxic training on glucose metabolism. Sedentary subjects underwent hypoxic training (FiO2 = 150%) for either 2 weeks (2-week group; n = 11) or 4 weeks (4-week group; n = 10). The 2-week group conducted training sessions on 6 days week 1 for 2 weeks, whereas the 4-week group conducted training sessions on 3 days week 1 for 4 weeks. Body fat mass or abdominal fat area did not change after training period _ 2max increased in both groups after training period (42 2 in either group. VO versus 43 2 ml min 1 kg 1 in 2-week group, 41 1 versus 42 2 ml min 1 kg 1 in 4-week group). Both groups showed a reduction in mean blood pressure after training period (92 3 versus 90 3 mmHg in 2-week group, 91 2 versus 87 2 mmHg in 4-week group, P≤005). No change was observed in blood glucose response after glucose ingestion after training period. However, area under the curve for serum insulin concentrations after glucose ingestion significantly decreased in only 4-week group (6910 763 versus 5812 872 lIU ml 1 120 min, P≤005). In conclusion, hypoxic training reduced blood pressure with independent on training duration. However, a longer period of hypoxic training led to greater improvements in insulin sensitivity compared with equivalent training over a shorter period, suggesting that hypoxic training programmes for more than 4 weeks might be more beneficial for improving insulin sensitivity.
Introduction Obesity and its associated complications, particularly metabolic syndrome and type 2 diabetes, are significant health problems that are becoming increasingly prevalent. Exercise under hypoxic condition may represent a new approach to prevent metabolic syndrome because hypoxic training was reported to decrease body fat mass (Wiesner et al., 2010), blood pressure (Schobersberger et al., 2003) and arterial stiffness (Nishiwaki et al., 2011) in various populations. Furthermore, hypoxic training confers greater improvements in insulin sensitivity compared with equivalent training under normoxic conditions in healthy people (Haufe et al., 2008) and in patients with type 2 diabetes (Mackenzie et al., 2011). We recently reported that a 4-week endurance training under hypoxic condition (FiO2 = 150%) resulted in a significant improvement in postprandial glucose regulation (insulin sensitivity) compared with endurance training under normoxic condition (Morishima et al., 2013). As an acute effect, endurance exercise at a simulated altitude of 2000 m was associated with enhanced 104
carbohydrate oxidation and blood lactate responses compared with exercise under normoxic conditions, but the serum free fatty acid (FFA) and glycerol responses to exercise were significantly impaired in hypoxic conditions (Katayama et al., 2010). Based on these findings, hypoxic stimuli facilitate glucose metabolism during exercise, resulting in improved insulin sensitivity. Although the mechanism involved in this response is not fully elucidated, it appears likely that enhanced skeletal muscle glucose uptake may be involved (Gamboa et al., 2011) because hypoxia itself stimulates the translocation of glucose transporter (Cartee et al., 1991). The improvements in insulin sensitivity in response to exercise training are influenced by several factors, including exercise intensity and duration, training frequency and the length of training period. The length of training period is particularly important among these factors because longer periods can lead to an apparent training effect, but may impede regular exercise in hectic lifestyles. Although traditional training regimens need to be several weeks (at least 4 weeks) to achieve adequate effects (Lim et al., 2008; Dela & Stallknecht, 2010;
© 2014 Scandinavian Society of Clinical Physiology and Nuclear Medicine. Published by John Wiley & Sons Ltd 35, 2, 104–109
Effect of short-term hypoxic training, T. Morishima et al. 105
Hordern et al., 2011), shorter training regimens may be more beneficial to complete exercise training programmes. From this context, the purpose of this study was to examine the effects of normobaric hypoxic training for either 2 or 4 weeks on glucose metabolism. We hypothesized that 2 weeks of hypoxic training would result in a similar improvement in insulin sensitivity to that observed over 4 weeks of hypoxic training.
Table 1
General characteristics before and after the training period. Before training
Age (years) Height (cm) Body weight (kg) BMI (kg m 2)
Methods Subjects Sedentary men [mean standard error (SE), age, 243 12 years; height, 1734 11 cm; body weight, 771 13 kg; body mass index (BMI), 255 07 kg m 2] participated in this study. The subjects were not participating in any training programmes at the start of this study. All of the subjects were informed about the experimental procedure and the purpose of the present study, and provided written informed consent. The study was approved by the Ethics Committee for Human Experiments at Ritsumeikan University, Japan. Experimental design and training procedure After completing the baseline measurements, the subjects were randomly assigned to either the 2-week hypoxic training group (2-week group; n = 11) or the 4-week hypoxic training group (4-week group; n = 10). There were no significant differences in the general characteristics between the two groups (Table 1). The subjects in the 2-week group participated in hypoxic training on 6 days week 1, whereas those in the 4-week group participated in hypoxic training on 3 days week 1. Subjects in both groups completed 12 training sessions. Each training session consisted of 60-min cycling at _ 2max) evaluated under 65% of maximal oxygen uptake (VO hypoxic conditions (FiO2 = 150%). The heart rate (HR) was continuously measured using a wireless monitor (Acculex Plus; Polar Electro Oy, Kempele, Finland) in all training sessions. Percutaneous oxygen saturation (SpO2, Smart pulse; Fukuda Denshi, Tokyo, Japan) and rating of perceived exertion (RPE) were monitored during the first and last training _ 2max and insusessions. Body composition, blood pressure, VO lin sensitivity (evaluated by an oral glucose tolerance test; OGTT) were determined before and after the period of the training regimen.
Measurements before and after the training period Maximal oxygen uptake _ 2max was determined using an incremental exercise test on VO a cycle ergometer (828E, Monark, Stockholm, Sweden). The test began at 60 W, and the load was increased progressively
SBP (mmHg) DBP (mmHg) Mean BP (mmHg) _ 2max VO (ml min 1) _VO2max/body weight (ml min 1 kg 1) TTE (s)
2 4 2 4 2 4 2 4 2 4 2 4 2 4 2 4 2 4
weeks weeks weeks weeks weeks weeks weeks weeks weeks weeks weeks weeks weeks weeks weeks weeks weeks weeks
2 weeks 4 weeks
24 25 174 173 79 75 26 25 134 131 69 70 92 91 3225 3033 42 41
After training 2 2 2 1 4 2 2 1 4 3 2 2 3 2 143 111 2 1
812 32 809 35
79 75 26 25 132 124 67 67 90 87 3323 3110 43 42
P-value
4 2 1 1 5 3 2 2 3 2 130 107 2 2
895 34 888 37
NS NS NS NS NS P
doi: 10.1111/cpf.12133
Effects of different periods of hypoxic training on glucose metabolism and insulin sensitivity Takuma Morishima1, Yuta Hasegawa1, Hiroto Sasaki1, Toshiyuki Kurihara2, Takafumi Hamaoka2 and Kazushige Goto2 1
Graduate School of Sport and Health Science, Ritsumeikan University, and 2Faculty of Sport and Health Science, Ritsumeikan University, Shiga, Japan
Summary Correspondence Kazushige Goto. Faculty of Sport and Health Science, Ritsumeikan University, 1-1-1, Nojihigashi, Kusatsu, Shiga 525-8577, Japan E-mail: [email protected]
Accepted for publication Received 17 October 2013; accepted 3 January 2014
Key words endurance training; insulin sensitivity; length of training period; normobaric hypoxia; short-term training
This study examined the effects of different periods of hypoxic training on glucose metabolism. Sedentary subjects underwent hypoxic training (FiO2 = 150%) for either 2 weeks (2-week group; n = 11) or 4 weeks (4-week group; n = 10). The 2-week group conducted training sessions on 6 days week 1 for 2 weeks, whereas the 4-week group conducted training sessions on 3 days week 1 for 4 weeks. Body fat mass or abdominal fat area did not change after training period _ 2max increased in both groups after training period (42 2 in either group. VO versus 43 2 ml min 1 kg 1 in 2-week group, 41 1 versus 42 2 ml min 1 kg 1 in 4-week group). Both groups showed a reduction in mean blood pressure after training period (92 3 versus 90 3 mmHg in 2-week group, 91 2 versus 87 2 mmHg in 4-week group, P≤005). No change was observed in blood glucose response after glucose ingestion after training period. However, area under the curve for serum insulin concentrations after glucose ingestion significantly decreased in only 4-week group (6910 763 versus 5812 872 lIU ml 1 120 min, P≤005). In conclusion, hypoxic training reduced blood pressure with independent on training duration. However, a longer period of hypoxic training led to greater improvements in insulin sensitivity compared with equivalent training over a shorter period, suggesting that hypoxic training programmes for more than 4 weeks might be more beneficial for improving insulin sensitivity.
Introduction Obesity and its associated complications, particularly metabolic syndrome and type 2 diabetes, are significant health problems that are becoming increasingly prevalent. Exercise under hypoxic condition may represent a new approach to prevent metabolic syndrome because hypoxic training was reported to decrease body fat mass (Wiesner et al., 2010), blood pressure (Schobersberger et al., 2003) and arterial stiffness (Nishiwaki et al., 2011) in various populations. Furthermore, hypoxic training confers greater improvements in insulin sensitivity compared with equivalent training under normoxic conditions in healthy people (Haufe et al., 2008) and in patients with type 2 diabetes (Mackenzie et al., 2011). We recently reported that a 4-week endurance training under hypoxic condition (FiO2 = 150%) resulted in a significant improvement in postprandial glucose regulation (insulin sensitivity) compared with endurance training under normoxic condition (Morishima et al., 2013). As an acute effect, endurance exercise at a simulated altitude of 2000 m was associated with enhanced 104
carbohydrate oxidation and blood lactate responses compared with exercise under normoxic conditions, but the serum free fatty acid (FFA) and glycerol responses to exercise were significantly impaired in hypoxic conditions (Katayama et al., 2010). Based on these findings, hypoxic stimuli facilitate glucose metabolism during exercise, resulting in improved insulin sensitivity. Although the mechanism involved in this response is not fully elucidated, it appears likely that enhanced skeletal muscle glucose uptake may be involved (Gamboa et al., 2011) because hypoxia itself stimulates the translocation of glucose transporter (Cartee et al., 1991). The improvements in insulin sensitivity in response to exercise training are influenced by several factors, including exercise intensity and duration, training frequency and the length of training period. The length of training period is particularly important among these factors because longer periods can lead to an apparent training effect, but may impede regular exercise in hectic lifestyles. Although traditional training regimens need to be several weeks (at least 4 weeks) to achieve adequate effects (Lim et al., 2008; Dela & Stallknecht, 2010;
© 2014 Scandinavian Society of Clinical Physiology and Nuclear Medicine. Published by John Wiley & Sons Ltd 35, 2, 104–109
Effect of short-term hypoxic training, T. Morishima et al. 105
Hordern et al., 2011), shorter training regimens may be more beneficial to complete exercise training programmes. From this context, the purpose of this study was to examine the effects of normobaric hypoxic training for either 2 or 4 weeks on glucose metabolism. We hypothesized that 2 weeks of hypoxic training would result in a similar improvement in insulin sensitivity to that observed over 4 weeks of hypoxic training.
Table 1
General characteristics before and after the training period. Before training
Age (years) Height (cm) Body weight (kg) BMI (kg m 2)
Methods Subjects Sedentary men [mean standard error (SE), age, 243 12 years; height, 1734 11 cm; body weight, 771 13 kg; body mass index (BMI), 255 07 kg m 2] participated in this study. The subjects were not participating in any training programmes at the start of this study. All of the subjects were informed about the experimental procedure and the purpose of the present study, and provided written informed consent. The study was approved by the Ethics Committee for Human Experiments at Ritsumeikan University, Japan. Experimental design and training procedure After completing the baseline measurements, the subjects were randomly assigned to either the 2-week hypoxic training group (2-week group; n = 11) or the 4-week hypoxic training group (4-week group; n = 10). There were no significant differences in the general characteristics between the two groups (Table 1). The subjects in the 2-week group participated in hypoxic training on 6 days week 1, whereas those in the 4-week group participated in hypoxic training on 3 days week 1. Subjects in both groups completed 12 training sessions. Each training session consisted of 60-min cycling at _ 2max) evaluated under 65% of maximal oxygen uptake (VO hypoxic conditions (FiO2 = 150%). The heart rate (HR) was continuously measured using a wireless monitor (Acculex Plus; Polar Electro Oy, Kempele, Finland) in all training sessions. Percutaneous oxygen saturation (SpO2, Smart pulse; Fukuda Denshi, Tokyo, Japan) and rating of perceived exertion (RPE) were monitored during the first and last training _ 2max and insusessions. Body composition, blood pressure, VO lin sensitivity (evaluated by an oral glucose tolerance test; OGTT) were determined before and after the period of the training regimen.
Measurements before and after the training period Maximal oxygen uptake _ 2max was determined using an incremental exercise test on VO a cycle ergometer (828E, Monark, Stockholm, Sweden). The test began at 60 W, and the load was increased progressively
SBP (mmHg) DBP (mmHg) Mean BP (mmHg) _ 2max VO (ml min 1) _VO2max/body weight (ml min 1 kg 1) TTE (s)
2 4 2 4 2 4 2 4 2 4 2 4 2 4 2 4 2 4
weeks weeks weeks weeks weeks weeks weeks weeks weeks weeks weeks weeks weeks weeks weeks weeks weeks weeks
2 weeks 4 weeks
24 25 174 173 79 75 26 25 134 131 69 70 92 91 3225 3033 42 41
After training 2 2 2 1 4 2 2 1 4 3 2 2 3 2 143 111 2 1
812 32 809 35
79 75 26 25 132 124 67 67 90 87 3323 3110 43 42
P-value
4 2 1 1 5 3 2 2 3 2 130 107 2 2
895 34 888 37
NS NS NS NS NS P
