Introduction
Starting school is a major stage of psychological and social adaptation and one of the most important periods of functional development [2,13]. Physical, social and personal development components are closely connected and actively forming and reorganising to meet school’s rapid pace [8,10]. The breadth of influences on the child at this time determines educational success and overall social and emotional stability [3]. Reduced activity, prolonged sitting and sharply increased gadget use lower pupils’ functional resilience [13].
Regular physical education and sport produce multifactorial changes in functional systems, enhancing adaptation and resistance to adverse influences [7,14]. Specialists are seeking to increase adaptive effects through nonspecific functional loads on the whole body or individual systems [6,9].
Some researchers regard hypoxic training alongside exercise as such a universal stimulus, improving functional state, work capacity and vitality [1,11,16]. Studies support its use both in healthy individuals and in treatment and rehabilitation of debilitated or ill people [12,15,17].
Despite national and international interest in hypoxic enhancement of functional resilience, questions about improving children’s capacities and physiological mechanisms remain poorly studied. We found no research on hypoxic training for physical development and functional resilience in primary-school children. Available publications lack data on children’s functional fitness.
We therefore aimed to study the influence of hypoxic training on physical development and functional fitness in children aged seven to eight.
Study organisation and methods
The study took place in Moscow general schools and involved 122 first- and second-grade pupils aged seven to eight. All were somatically healthy and cleared for physical education.
An eight-month programme of breath-holding and physical activity during breath holds was proposed to assess cardiorespiratory changes and indirect hypoxic tolerance. Experimental work had two stages.
At the first stage, a baseline experiment assessed functional fitness in children aged seven to eight. Three groups were formed from its results: an experimental group of 42 children and two control groups of forty each. Comparing hypoxic and functional resilience with two controls rather than one was necessary to evaluate the proposed hypoxic-training method while excluding the effect of swimming itself, which substantially trains the cardiorespiratory system.
A formative experiment then tested the developing method. The experimental group (EG) and control group 1 (CG1), besides one weekly pool lesson, swam twice more weekly. EG sessions additionally included interval and maximal voluntary breath holds, underwater swimming, collecting objects from the bottom and swimming varying distances while holding the breath, totalling ten minutes of hypoxic work. CG2 swam once weekly as the third physical education lesson; all also practised football, martial arts or dance at least twice weekly.
EG and CG1 sessions ran in parallel, each lasting forty-five minutes.
To determine the participants’ cardiorespiratory response, a standard hypoxic load lasting fifteen seconds was proposed. Using a RI-FOX pulse oximeter from Riester, Germany, heart rate and blood oxygen saturation (SpO2) were recorded: resting heart rate, resting saturation, heart rate immediately after the standard breath hold, and saturation immediately after that breath hold.
Heart-rate response was the post-hold-to-resting heart-rate ratio. Chest circumference, height and weight assessed morphological and functional changes. Vital capacity used Spirotest 5260, Riester, Germany. Statistical significance used Student’s t-test, p<0.05.
Results and discussion
Despite individual variation, physical-development measures were within age norms [10]. Height ranged 126.32–128.19 cm (Table 1). Additional swimmers, EG and CG1, were slightly taller and lighter than children in other sports, CG2, without significant differences. This may reflect aerobic training and initial selection, since ectomorphic children more often choose swimming [5]. Smaller chest circumference in swimmers supports this interpretation.
Baseline vital capacity, reflecting respiratory functional performance, was highest in CG1 and lowest in CG2.
Repeat measurement of morphological and functional parameters revealed the following trends. Height increased by approximately five centimetres in all groups. The greatest body-weight increase occurred in control group 2. Relative to baseline, this group gained 6.93%, compared with 3.31% in control group 1 (Figure 1).
Vital capacity and chest circumference increased most in EG and CG1, the additional swimmers. Significant changes occurred only in EG, which also performed hypoxic loads. Vital capacity rose 22% in EG, 11% in CG1 and 5% in CG2.
Efficient bodily functioning reflects functional fitness [12], expressed here as lower frequency and greater volume parameters of autonomic systems [4]. Cardiorespiratory resilience testing identified the following patterns.
Resting oxygen saturation agreed with literature despite minor variation [6,11]. Values were 96–99%, averaging 98.43% (Table 3). Training scarcely affected saturation, with changes no greater than 1%.
At baseline, the standard hypoxic test lowered saturation and increased heart rate (Figure 2). After fifteen seconds of breath-holding, EG heart rate rose an average eleven beats/min and blood oxygen fell 8%. Controls showed the same pattern: SpO2 declined 7% in CG1 and 6% in CG2, with heart-rate increases of seventeen and twelve beats/min, respectively.
Baseline heart-rate response ratios were similar, 1.11–1.17 units. Normally the ratio should not exceed 1.2 [6]; higher values indicate an unfavourable cardiovascular response and marked adaptive strain during hypoxic or other loads [4,7].
The developed method combined breath-holding at relative muscular rest with hypoxic swimming exercises and different forms of underwater swimming.
All functional measures were repeated in April after the intervention. Resting cardiorespiratory function changed substantially; EG resting heart rate decreased significantly by 12% from baseline (Figure 2).
Resting heart rate changed less in controls: 1% in CG1 and 7% in CG2.
The standard hypoxic test showed that the intervention directly improved cardiorespiratory functional economy.
EG heart rate after the fifteen-second hold declined significantly to 91.71 versus 107.44 beats/min initially. The response ratio was 1.08 versus 1.11, a significant difference (p<0.05), indicating smaller cardiovascular shifts and better adaptation. Control changes were small and nonsignificant.
Only EG showed a significantly smaller post-test oxygen-saturation decline. Before breath-hold training, SpO2 fell 7.92%, similar to controls; afterward it fell only 0.33%. Controls remained essentially unchanged.
Conclusions
1. Hypoxic training does not significantly influence physical development. Functional changes, by contrast, are directly related to breath-holding exercises.
2. Hypoxic training improves functional fitness in seven- to eight-year-olds, significantly increasing cardiorespiratory economy and reducing the response to a standard breath-holding test.
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Full main-text translation of: Чайка Ж.Ю., Абрамов Г.О., Зверева А.А., Сороченкова М.В. Влияние гипоксической тренировки на функциональную подготовленность детей 7–8 лет. Новые исследования. 2021;3(67):31–39. DOI:10.46742/2072-8840-2021-67-3-31-39.
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