Autor(es): Dr. Masoumeh Hosseini, Dr Naser Behpoor
Background & Objective: Regular and long term training causes physiological adaptation in heart which is in contrast with pathological adaptation. The objective of this study was to compare the structural and functional status of the heart in Iran’s elite male and female mountaineers .
Materials and Methods: The study’s sample consisted of twenty professional male and female mountaineers with mean age of 285.3 yrs, height of1739.6 cm, weight of 7313.61 kg, 6±1/7 yrs of continuous membership in the national team and 10/5±4/2 yrs of regular training in the mentioned course. All participants were healthy and were selected as available sampling. In resting status, heart rate, PR interval, the distance of ST segment from isoelectric line and T-wave voltage were measuring using electrocardiography and ejection fraction, LV end-diastolic and end-systolic diameters, thickness of heart walls, LV mass and LV mass index were measured using echocardiography, all acting as structural and functional parameters.
Results: Data analysis using t-student test showed that PR interval, T-wave voltage, the distance of ST segment from isoelectric line, LV end-diastolic diameter, LV mass & mass index, intra ventricular wall thickness & index and post LV wall thickness in the male group were all significantly more than those of the female group (p≤0.05). There was no significant difference between two groups for the other variables.
Conclusion: The structural and functional variables of male mountaineers’ hearts were observed to be better and higher than the female mountaineers, probably due to longer periods of training and larger body size.
The ability and capacity of an individual in performing athletic activities depends upon the function and efficiency of various body systems. Athletic exercise causes structural and functional changes in the heart of athletes, especially in the left ventricle. These changes are called “Heart Adaptations”, i.e. physiological changes, which are in contrast with pathological ones.
Physiological effects of these exercises mostly depend on the sport’s nature and style . Performing definite endurance sports increases the number of Mitochondria and Myofibrils in cardiac muscle cell, and increasing parasympathetic capability of the body considerably decreases resting pulse rate. Also conduction of electrical impulses becomes slower, which results in longer PR distance . Normally the ST segment is on the isoelectric line, but in athletes, because of ventricular hypertrophy and early ventricular Repolarization this segment rises above this line, and ventricular hypertrophy may cause registration of higher voltages for the T wave . Continuous or endurance athletic activities apply high volume pressures on the cardiac muscles, increasing the size of the chambers and thickness of ventricular walls. These changes are the pattern of eccentric hypertrophy . The majority of changes occur in the left ventricle, the most active heart chamber. End diastolic volume increases and because of thicker walls, the ventricle contraction is stronger which in turn increases stroke volume and ejection fraction and decreases end systolic volume. However, differences between individuals results in different responses to athletic exercises. Genetic is the major cause of variation in reactions .
Gates and et al (1999) compared the heart structure and function of elite male and female endurance skiers and observed that the LV end diastole, intra ventricular wall and post LV wall thicknesses and LV mass is significantly higher in male hearts . Fagard (2003) studied the heart of male and female endurance runners and found out that there was no significant difference between variables of pulse rate, PR distance and resting T wave voltage in the two groups .
Numerous studies have been performed on functional and structural condition of heart in various athletic fields, such as marathon running, swimming and skiing with emphasis on differences between genders. Some have found these differences insignificant and some have confirmed them [4, 6, 7, 8, 9, 10, 11, 12]. As respiration system goes under intense pressures in higher altitudes, cardiovascular system undergoes changes to compensate the decrease in the PaO2 caused by increase in altitude. Long term activities requiring oxygen transportation and aerobic energy system are more affected by low pressure environmental conditions in high altitudes [1, 12]. Therefore, gender related differences between male and female athletes, especially in blood volume and various body types, a scant number of studies performed about gender differences in mountaineers, contradictory results of previous studies and also higher altitude records for elite male mountaineers suggested the this theory that functional and structural condition of male and female mountaineers’ heart is different.
In this study the structural and functional condition of male and female mountaineers’ heart in resting status is examined and compared using electrocardiography and echocardiography, so it can be determined whether there is a difference between structural and functional condition of male and female mountaineers’ heart.
20 member of national mountaineering team were selected as available samples in two male (N=10) and female (N=10) groups, whom were a continuous member of Iran’s national mountaineering team for a mean of 6 years and a mean previous athletic practice of 10.5 years with regular weekly trainings (1 climb to 3500 – 4500 meters altitudes and 1 climb to 2500-3000 altitudes), no previous record of cardiac and vascular ailments, smoking or heart affecting drugs and completely healthy. Before carrying out the study, necessary information were parted with them explaining the method in which tests were to be performed and that they were completely harmless, also that all medical information related to the subject shall remain confidential. Then the subjects filled out the sport medicine questionnaire and signed permission forms. The general specifications of subjects are presented in Table 1.
Measuring Functional and Structural Variables of Heart
To study and compare functional and structural variables of male and female national team mountaineers’ heart in resting status, the subjects lied down for 5 minutes on the special bed and the variables : Number of heartbeats, PR distance, ST segment distance from isoelectric line and T wave voltage were measured using electrocardiogram record for both groups. Then by using one-dimensional and bi-dimensional echocardiography, LV ejection fraction percentage (EF%), intra ventricular wall thickness, post LV wall thickness, LV mass, LV end diastole and end systole diameter of both group were recorded and by providing height and weight inputs of subjects to the computer, all echocardiographic variables were adjusted according to the body surface level for more accurate comparisons.
All measuring procedures were performed in the Echo and Sports Test section of Rasoul Akram Hospital in three consecutive days under similar local and temperature conditions by a cardiovascular specialist supervised by the researcher using electrocardiography machine (Siemens, Made in Germany) and echocardiogram machine (Wing Mode, Made in USA, HP Sonos 1500).
Descriptive statistics were used to calculate means, variances and variation percentage of means. For hypothesis testing T-Student method was used and significance level of P ≤ 0.05 was selected in addition to observing all presumptions of this test. Statistical calculations were performed by SPSS software (version 13).
Table 2 demonstrates values related to structural and functional properties of heart for both groups.
By examining the study’s variables in both groups it was revealed that PR distance, ST segment distance from isoelectric line and T wave voltage, end diastole diameter, LV mass, post LV wall thickness and intra ventricular wall thickness of men were significantly higher than those of women (P ≤ 0.05). When echocardiography data were adjusted according to body surface of subjects, the remaining significantly different variables were LV mass and intra ventricular wall thickness, other variables were no more significantly different (P ≤ 0.05).
Comparing cardiac condition of study’s subject (male and female) indicated that there are significant differences between variables of PR distance, ST segment distance from isoelectric line and T wave voltage, end diastole diameter, LV mass and ventricular wall thicknesses of two genders.
Examining the variables resulted from electrocardiogram during resting status of male and female athletes showed that there is no significant difference between resting pulse rate of male and female athletes. This finding conforms to that of Fagard’s (2003), in which resting pulse rate of male and female athletes demonstrated no significant difference , while Wrested & Ekman (2002) study indicated a significant difference between resting pulse rate of male and female athletes . The difference in results can be attributed to type, intensity, duration of endurance sport and athletic record of subject.
The findings of study also indicated a significantly longer PR distance in male subjects compared to female ones, which conforms to that of Bjornstad’s (1992) , while Fagard (2003) observed no significant difference between PR distances of male and female athletes  which is in contrast with study’s findings.
PR distances depends upon number of heartbeats , although the mean heartbeats of the two groups were not significantly different, the PR distances were. This can be interpreted that there is no evident relation between resting pulse rate and PR distance. Bjornstad (1993) also observed a longer PR distance in athletes with LV hypertrophy, while there was a slight decrease in their heartbeat and concluded that elongation of PR distance has little relation with pulse rate and mostly is because of LV hypertrophy . Probably longer training sessions, climbing to higher altitudes and hypertrophy in LV contributes to longer PR distances of male subjects compared to female ones.
In this study the mean rise of ST segment from isoelectric line in male athletes (0.95 mm) compared to female athletes (0.45 mm) were significantly different. The phenomenon of ascending ST segment in healthy individuals is caused by early repolarization. Rising ST segment in athletes is not similar to ones occurring in cardiac ischemia, but it must be noted that ST segment position in athletes can change, just like a patient with ischemia [15, 16]. The difference between mean ST segment length of male and female subjects can be attributed to smaller ventricular mass in women. Wrested & Ekman (2002) study also showed higher ST segment in men compared to women . In contrast, Fagard (2003) and Langdeau (2001) observed no significant difference between ST segment length of male and female endurance athletes [6, 17]. The probable explanation for these contradictions can be attributed to intensity and duration of activity, type of sport and athletic record of subjects.
In current study mean T wave voltage in male athletes were significantly higher than that of the female ones. T wave alterations in athletes are essentially because of changes caused by repolarization of ventricles resulting from ventricular hypertrophy. It must be noted that ST length and T wave alterations are among the main repolarization changes in athletes and occurred only in athletes with intense trainings [15, 16]. The findings of current study are in contrast with those of Sharma’s (1999) , while conformed to that of Langdeau’s (2001) .
Comparing echocardiography variables of male and female athletes in the current study showed a significantly higher end diastole diameter in men than that of women. But after adjustment of this variables based on body surface level of subjects, the difference was eliminated. This difference was probably caused by higher blood volume and larger ventricular chamber in men, in addition to higher altitude experience and longer durations of activity in male subjects. Gates (1999) performed a study on elite male and female endurance skiers and observed that men had higher end diastole diameter compared to women . In contrast, Wrested & Ekman (2002) demonstrated that male and female endurance runners had no significant difference in LV end diastole diameter . The reasons for this contradiction are probably different assessment methods, different sports field and athletic record of subjects.
Mean LV end systole diameter of men was not significantly different than that of women’s. Wrested & Ekman (2002) and Hoogsteen (2004) also found no significant difference between elite male and female endurance athletes [7, 19]. In the current study the EF% of men showed no significant difference when compare to that of women’s. Considering the lack of significant difference for LV end systole diameter of the two groups, this result can be interpreted. When examining the EF%, and increase in EF% is observed in both groups that can be attributed to mountaineering exercises. Mean EF% was 76% for male and female athletes, with a considerable increase from normal individuals and normal conditions (60%) . Gates (1999) studies showed that EF% in exercised women increases more than normal percentages . Also Schneider (2002) study demonstrated considerably higher EF% in male mountaineers compared to normal percentage .
The study’s findings indicated significant difference between mean intra ventricular and post LV wall thicknesses in male group compared to female group. But after adjustments according to body surface level the difference in post LV wall variable was eliminated. These differences are probably caused by larger body, cardiac volume and mass in addition to longer record of athletic activity and climbing to higher altitudes. The results of current study conformed to that of Gates’ (1999) and Hoogsteen’s (2004), but were in contrast with that of Wrested & Ekman’s (2002) . This contradiction is probably because of difference in sports fields, duration, intensity and type of trainings and different statistical population of subjects .
The current article the amount of LV mass in men (208 g) compared with that of women’s (125 g) and mean LV mass index of men (92 m²/g) compared with that of women’s (61 m²/g) showed a significant difference. These differences are probably caused by longer athletic record and higher altitude climbs in men. In Maron study, 46% of male endurance athletes had LV hypertrophy . Wrested & Ekman’s (2002) observed significant difference in elite men and female endurance athletes for LV mass variable . Gates (1999) came upon similar results in comparing elite male and female endurance skiers. But when data adjustments were performed according to body surface levels, the differences were eliminated .
Because researchers used various sports fields and methods for assessments, these factors may have contributed to contradictory conclusions in various studies and sometimes difference results due to genetic and environmental factors. It is noteworthy that lack of control group and small number of test subjects, that are among the shortcomings of this study, extending the results to other cases should be practiced with less degree of reliance.
The result of this study is that the heart of athletes, especially the left ventricle grows larger due to sports activity. This hypertrophy causes no failure in general function of the heart, even improves the function of it, especially that of the left ventricle. The findings of this study showed that structural and functional condition of elite male and female mountaineers are in physiological conditions and cardiac variables of male mountaineers were observed to be in better and higher levels that those of female mountaineers, probably because of larger body, longer and more intense athletic activity and climbing to higher altitudes. in conclusion, in order to improve the function and efficiency of cardiac muscle, mountain climbing is recommended for healthy individuals, especially the athletes.
I’d like to hereby express my gratitude towards men and women of Iran’s national mountaineering team because of their participation in this study.
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Table 1 – General specifications of subjects
Table 1. A comparative Study of the Heart Status in Elite Male and Female Mountaineers
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The amounts are in terms of mean and standard deviation.
Table 2 – Comparison of electrocardiography and Echocardiography findings in male and female athletes
Table 2. A comparative Study of the Heart Status in Elite Male and Female MountaineersContenido disponible en el CD Colección Congresos nº 16*
Significant in comparison between the two groups (p≤0.05