Cardiorespiratory responses to incremental exercise in dominant somatotypes

INTRODUCTION

Somatotype rating is used to categorise human physiques using parameters related to body shape and composition. These parameters are adiposity, musculoskeletal robustness and linearity or slenderness. W.H. Sheldon first used the word “somatotype” in 1940.^[1] The word ‘somatotyping’ today refers to a variety of method-specific procedures, all of which are based on the original Sheldonian notions and use a three-component rating system. Heath and Carter pioneered the most frequently utilised somatotyping technique. This technique has three components – endomorphy, mesomorphy and ectomorphy – that empirically characterise relative fatness, relative musculoskeletal development and relative body linearity, respectively.^[2] For example, a 2-5-1 rating expressed in this form would read as two for endomorphy, five for mesomorphy and one for ectomorphy. Thus, these figures indicate the magnitudes of the three components. A rating of ½–2½ for a component is considered low, 3–5 is considered moderate, 5½–7 is high, and 7½ and above is very high.^[3]

It is known that anthropometric parameters influence the ability to perform physical activity. Heath and Carter’s anthropometric method of somatotype determination takes into consideration ten anthropometric parameters. These are height, weight, skinfold thickness (triceps, subscapular, supraspinal and medial calf), bone breadth (bi-epicondylar humerus and femur) and limb girth (arm flexed and tensed calf). It is a better predictor of body composition than other methods.^[4] Compared to only using body mass index (BMI) and waist-hip ratio, this technique provides more accurate data on body composition. Thus, somatotype is a crucial component of someone’s physical fitness and health profile. During physical activity and training, people of various somatotypes exhibit unique performance capabilities.^[5] It has been demonstrated that the dominant somatotype affects functional responses during maximal exercise.^[5,6]

Cardiopulmonary exercise testing (CPET) offers a comprehensive evaluation of integrative exercise responses encompassing the pulmonary, cardiovascular, hematopoietic, neuropsychological and skeletal muscle systems that are not adequately reflected by the measurement of individual organ system function.^[7] Hence, the objective of the present study was to measure cardiorespiratory responses to incremental exercise in different somatotypes.

MATERIALS AND METHODS

This study was approved by the Institute Ethics Committee for Human Subjects (Ref. No.: IECPG-520/23.09.2021, RT-02/28.10.2021 dated 29.10.21).

Written informed consent was taken from all participants as per the institute’s ethical norms.

RESULTS

CPET finding in different somatotypes

We examined the absolute values and percentage predicted values of CPET parameters in various somatotypes, as shown in Table 2 and Figures 1-3. We found that mesomorphs significantly outperformed endomorphs in terms of peak VO₂, peak VO₂ %predicted, peak VO₂/kg, peak VO₂/kg %predicted, METS, METS %predicted, V.E, oxygen pulse (O₂ pulse) and VE/VO₂ values. In contrast, ectomorphs significantly outperformed endomorphs in terms of peak VO₂/kg and METS values. Mesomorphs achieved significantly lower maximum HR during exercise than ectomorphs and had significantly smaller BR than endomorphs and ectomorphs but significantly higher %predicted O₂ pulse compared to endomorphs and ectomorphs. Other parameters were comparable.

Table 2: This graph displays the parameters of the cardiopulmonary exercise test in different somatotypes.

CPET parameters	Endomorphs (n=20)	Mesomorphs (n=15)	Ectomorphs (n=15)	P-value
Peak oxygen consumption (mL/min)	2151±287.8	2487±364.3	2342±403.8	Pa=0.01
Peak oxygen consumption (%predicted)	66.96±10.11	78.13±11.95	70.06±8.18	Pa=0.003
Peak oxygen consumption/kg	30.11±5.52	36.04±6.16	38.32±5.38	Pa=0.0057 Pb<0.0001
Peak oxygen consumption/kg (%predicted)	66.96±10.11	78.13±11.95	70.06±8.18	Pa=0.003
METS	8.77±1.86	10.29±1.74	10.95±1.54	Pa=0.026 Pb=0.0004
METS %predicted	66.92±10.09	78.13±11.95	70.06±8.18	Pa=0.003
RQ	1.27 (1.05–1.58)	1.31 (1.15–1.58)	1.26 (1.09–1.44)	P=0.80
BR	53.80±17.16	38.38±11.87	52.79±9.47	Pa=0.004 Pc=0.001
Tidal volume (L (btps))	1.78±0.50	2.03±0.41	1.99±0.40	P=0.17
V.E	71.13±25.39	95.32±18.63	80.29±14.43	Pa=0.002
Respiratory frequency (1/min)	38.19±6.89	48.25±11.34	40.92±7.03	Pa=0.001 Pc=0.03
O2 pulse (mL/beat)	12.80 (9.20–21.90)	14.80 (10.30–24.00)	12.85 (10.10–18.50)	Pa=0.02
O2 pulse %predicted	77.50 (51.00–115.00)	90.00 (67.00–147.00)	76.50 (17.60–98.00)	Pa=0.006 Pc=0.033
HR (bpm)	171.5 (142.00–194.00)	166.00 (125.00–186.00)	178.00 (159.00–189.00)	Pc=0.04
HR % predicted	87.23±8.673	82.67±10.55	88.94±5.418	P=0.097
HRR (bpm)	23.00 (5.00–54.00)	20.50 (9.00–55.00)	17.00 (4.00–36.00)	P>0.99
VE/VO2	34.24±5.99	39.40±7.02	35.80±5.82	Pa=0.03
VE/VCO2	27.45 (19.50–42.40)	29.10 (25.60–40.50)	26.55 (23.00–34.50)	P=0.17
OUES	2550±422.9	2647±414.2	2645±447.8	P=0.70
OUES (%predicted)	81.00±14.04	83.80±10.01	83.72±12.23	P=0.70
VO2 at anaerobic threshold (mL/min)	1686±406.1	1651±326.2	1795±382.5	P=0.51
VO2 at anaerobic threshold (%pred)	75.40±16.02	66.73±11.02	76.89±13.93	P=0.09
End-tidal PO2 (PetO2)	105.7±6.41	109.7±4.60	106.2±4.60	P=0.07
End-tidal PCO2 (PetCO2)	44.04±6.26	39.87±4.82	42.78±4.50	P=0.06

aEndomorphs vs. Mesomorphs, ^bEndomorphs vs. Ectomorphs, ^cMesomorph vs. Ectomorphs. Values presented are mean±standard deviation or median (minimum–maximum), analysed by one-way Analysis of Variance (post hoc-Tukey) or Kruskal–Wallis test (post hoc-Dunn’s), respectively. OUES: Oxygen uptake efficiency slope, METS: Metabolic equivalent, RQ: Respiratory quotient, BR: Breathing reserve, HR: Heart rate, HRR: Heart rate reserve, VE/VO₂: Ventilatory equivalents for oxygen, VE/VCO₂: Ventilatory equivalent for carbon dioxide, O₂: Oxygen pulse, V.E: Minute ventilation, PO₂: partial pressure of O₂, PCO₂: partial pressure of CO₂

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Figure 1:

The graphs depicting cardiopulmonary exercise parameters in different somatotypes: (a) Peak VO₂ (b) Peak VO₂ %predicted (c) Peak VO₂/kg (d) Peak VO₂/kg % predicted (e) METS (f) METS % predicted Values are plotted as mean ± standard deviation or median (minimum to maximum). *P < 0.05, **P < 0.01 and ***P < 0.001, ****P ≤ 0.0001 for inter group comparison. VO₂: Peak oxygen consumption; METS: Metabolic equivalent in exercise testing.

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Figure 2:

The graphs depicting the cardiopulmonary exercise parameters in different somatotypes: (a) Minute ventilation, (b) Respiratory frequency (c) Breathing reserve (d) Tidal volume, (e) Heart rate, (f) Heart rate % predicted. Values are plotted as mean ± standard deviation or median (minimum to maximum). *P < 0.05, **P < 0.01 for inter group comparison.

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Figure 3:

The graphs depicting the cardiopulmonary exercise parameters in different somatotypes: (a) Heart rate reserve (b) Oxygen pulse (c) Oxygen pulse % predicted (d) PetO₂ (e) PetCO₂ (f) VE/ VO₂. Values are plotted as mean ± standard deviation or median (minimum to maximum). *P < 0.05, **P < 0.01 and for inter group comparison. petO₂: End-tidal PO₂; PetCO₂: End-tidal PCO₂; VE/VO₂: Ventilatory equivalent for oxygen.

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Correlation between determinants of somatotype and the parameters of CPET

We investigated the correlation between somatotype determinants and the cardiopulmonary exercise test parameters listed in Table 3 and Figure 4. Weight had a positive correlation with O₂ pulse and OUES. BR, VO₂ at anaerobic threshold, VO₂ at anaerobic threshold %predicted, and OUES all showed positive correlations with height. Humerus breadth was positively correlated with OUES. Arm girth was inversely associated with HR but positively correlated with O₂ pulse and VE/VCO₂ slope. Calf girth was positively correlated with oxygen pulse but negatively correlated with peak VO₂/kg, METS, breathing reserve, heart rate and heart rate % predicted.

Table 3: Correlation between determinants of somatotype and cardiopulmonary exercise test parameters.

Spearman correlation	Weight	Height	Humerus breadth	Arm girth	Calf girth
Peak VO2/kg	r=−0.55	r=0.02	r=−0.11	r=−0.49	r=−0.37
	P=5.48	P=0.86	P=0.40	P=7.73	P=0.003
METS	r=−0.50	r=0.06	r=−0.05	r=−0.48	r=−0.33
	P=3.82	P=0.62	P=0.70	P=1.08	P=0.009
BR	r=0.03	r=0.39	r=0.01	r=−0.22	r=−0.10
	P=0.77	P=0.002	P=0.91	P=0.08	P=0.45
HR	r=−0.18	r=0.12	r=−0.17	r=−0.35	r=−0.34
	P=0.16	P=0.28	P=0.18	P=0.005	P=0.007
HR %pred	r=−0.03	r=−0.11	r=−0.16	r=−0.19	r=−0.26
	P=0.79	P=0.33	P=0.22	P=0.14	P=0.04
VO2/HR	r=0.29	r=0.14	r=0.21	r=0.26	r=0.29
	P=0.02	P=0.26	P=0.09	P=0.04	P=0.02
VO2 at AT	r=0.24	r=0.36	r=0.13	r=0.05	r=0.15
	P=0.06	P=0.004	P=0.29	P=0.69	P=0.23
VO2 at AT %pred	r=0.15	r=0.27	r=0.07	r=3.80	r=0.09
	P=0.24	P=0.03	P=0.55	P=0.99	P=0.47
Respiratory compensation	r=0.29	r=0.17	r=0.01	r=0.22	r=0.15
	P=0.02	P=0.18	P=0.89	P=0.08	P=0.23
VE/VCO2 slope	r=0.11	r=−0.14	r=0.08	r=0.29	r=0.17
	P=0.40	P=0.27	P=0.54	P=0.02	P=0.18
OUES	r=0.32	r=0.35	r=0.27	r=0.12	r=0.27
	P=0.01	P=0.006	P=0.03	P=0.33	P=0.03

In this correlation, P values and r-values are presented, and the bold text represents a significant correlation analysed by the Spearman correlation test. METS: Metabolic equivalent, HR: Heart rate, BR: Breathing reserve, AT: Anaerobic threshold, VE/VCO₂: Ventilatory equivalent for carbon dioxide, OUES: Oxygen uptake efficiency slope, VO₂: Oxygen consumption

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Figure 4:

The graphs show correlation between somatotype dimensions and cardiopulmonary exercise test parameters. Calf girth correlates negatively with (a) peak VO₂/kg and (b) METS. Height correlates positively with (c) breathing reserve and (d) VO₂ at anaerobic threshold. Arm girth correlates positively with (e) VO₂/HR. Calf girth correlates positively with (f) VO₂/HR. Arm girth correlates positively with (g) VE/VCO₂ slope.

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DISCUSSION

In the present study, cardiorespiratory responses to incremental exercise have been investigated in young adults having dominant somatotypes.

Compared to other approaches, the Heath and Carter method is a better predictor of body composition since it accounts for variables including height, weight, skinfold thickness, bone width and limb girths. This approach offers more precise information on body composition than BMI and waist-hip ratio alone.

Mesomorphs having higher muscle mass compared to endomorphs may explain their significantly higher peak VO₂, peak VO₂% predicted, peak VO₂/kg and peak VO₂/kg% predicted compared to endomorphs. Imms et al. have reported greater oxygen consumption during contraction of the large mass muscle (quadriceps) than that during small mass muscle (hand gripping) at 20% maximum voluntary contraction.^[9] The significantly lower values in endomorphs may be explained by their comparatively slower metabolism, which causes more fat accumulation in the body. Pourhassan et al. studied the relationship between submaximal oxygen uptake and body composition and reported a strong association between VO₂submax and fat-free mass (FFM) and concluded that FFM is the determinant of VO₂ submax.^[10] Saha has determined the impact of somatic and body composition variables on aerobic capacity in different somatotypes. She observed a negative correlation between VO₂ max and body fat percentage, body surface area and endomorphy component of somatotype, while it correlated positively with the lean body mass, percentage of skeletal muscle mass and mesomorphy component of somatotype.^[11] Oda et al. also reported a significant negative correlation between peak oxygen uptake with total body fat percentage.^[12] These findings suggest that VO₂max is influenced by the total active muscle mass being recruited during exercise, where the more muscle mass is involved during exercise, the higher the VO₂max.^[13]

A MET is the quantity of oxygen consumed while at rest, the value of which is around 3.5 mL O₂/kg/min (1.2 kcal/min for a person weighing 70 kg). The MET concept offers a straightforward, understandable method for describing the energy expenditure of physical activity as a multiple of resting metabolic rate. The energy cost of an activity may be calculated by dividing the relative oxygen cost of the activity (ml O₂/kg/min) by 3.5.^[14] In the present study, METS values were significantly lower in endomorphs than other somatotypes for maximum physical activity. The amount of skeletal muscle is a key factor in the rise in metabolism during exercise and the absolute maximum oxygen consumption. Lean tissue has a significant relationship with basal metabolism, and skeletal muscles are the source of energy used during physical activity.^[15] This might be the reason why mesomorphs achieved higher METS than endomorphs. Thus, higher VO2peak/kg and METS values observed in mesomorphs may be explained by the higher muscle mass in these individuals.

In an exercising person, maximal oxygen uptake is limited by the ability of the cardiorespiratory system to deliver oxygen to the exercising muscles.^[16] The increase in the O₂ pulse after the training session may reflect the degree of peripheral and cardiac adaptation to training. In our study, we observed that O2 pulse (the amount of oxygen consumed per heartbeat during exercise), which can be used as an indirect indicator of cardiac stroke volume,^[17] was significantly higher in mesomorphs as compared to endomorphs. Chaouachi et al. have also reported higher values of O₂ pulse in mesomorphs in comparison to the endomorphs and ectomorphs’ groups.^[18] We also observed that O₂ pulse significantly correlated with arm and calf girths. The calf muscle pump plays a very important role in increasing venous return, which can also affect the cardiac output.

We found that mesomorphs had significantly higher V.E than endomorphs, and respiratory frequency was significantly higher compared to endomorphs and ectomorphs, but the BR was significantly lower as compared to endomorphs and ectomorphs. While exercising, VTs and respiratory rates are increased, increasing oxygen consumption. This is generally achieved by raising the respiratory rate because VTs are frequently not raised. Uneven body fat distribution may restrict diaphragmatic excursion and impede further VT augmentation during exercise.^[19] Mesomorphs have a significantly smaller BR, which may be related to their increased V.E.

Subhan et al. reported that there is no significant difference in maximal HR achieved during exercise among persons who are overweight, normal weight and obese as determined by BMI.^[20] Nevertheless, we noticed that ectomorphs achieved significantly higher maximal HR during exercise than mesomorphs. The reason behind this is not yet clear.

High airway resistance might be the cause of the VE/VO₂ and VE/VCO₂ not rising with maximum activity.^[21] We found that VE/VO₂ was significantly higher in mesomorphs than in endomorphs. This may be a result of their significantly higher respiratory frequency and V.E. One of the possibilities might be that endomorphs have a significantly higher peripheral airway resistance, leading to a decreased VE/VO₂ ratio.

Mesomorphs have a higher percentage of muscular components, and endomorphs have relatively more body fat than mesomorphs.^[22] Excess body fat may exert an unfavourable burden and a hindering action on cardiac function, particularly during exhausting exercise when excessively hyperactive body muscles fail to uptake enough oxygen due to the deposition of a proportionately higher amount of fat mass. Extra body fat affects mechanical efficiency for a given workload and impairs cardiorespiratory functions.^[23]

CONCLUSION

Mesomorphs have higher peak oxygen consumption than endomorphs, along with higher METS, V.E and O₂ pulse. Clinicians should consider somatotype when interpreting the results since, even though all the participants were in good health, there is still variation in their cardiorespiratory responses.