Breathing Training Beats Jump Training for Young Runners’ Lungs, and Their Pupils Reveal Why

In a finding that could reshape how coaches prepare adolescent distance runners, a randomized controlled trial has shown that twelve weeks of inspiratory muscle training produced substantially larger gains in lung function than plyometric jump training in youth middle-distance athletes. More intriguingly, the two training styles left distinct fingerprints on the athletes’ pupillary light reflex, a non-invasive window into the autonomic nervous system, suggesting that different forms of conditioning may sculpt not just muscles and lungs but the very neural circuits that regulate them.

The study, published in Frontiers in Physiology, recruited ninety competitive runners aged fourteen to eighteen from regional athletics clubs and schools in Tamil Nadu, India. All were experienced middle-distance athletes competing in events from 800 meters to 3000 meters, with at least two years of structured training and a current volume of four or more sessions per week. The researchers randomly assigned thirty participants each to an inspiratory muscle training group, a plyometric training group, or a control group that continued normal running routines. Eighty-six participants, or 95.6 percent, completed the full twelve-week protocol and were included in the primary analysis.

The inspiratory muscle training protocol was demanding and precisely dosed. Using threshold devices that provide consistent resistance throughout the inspiratory range of motion, athletes performed thirty inspiratory efforts twice daily, five days per week, amounting to three hundred efforts weekly. Training intensity began at 30 percent of each athlete’s maximal inspiratory pressure in the first week and progressed by five percentage points weekly, reaching 75 percent by week ten and holding at 80 percent through week twelve. Weekly assessments of maximal inspiratory pressure allowed the load to be adjusted as the respiratory muscles strengthened, applying the same progressive-overload principle that weightlifters use for skeletal muscle.

The plyometric group, by contrast, trained three times per week in supervised sessions lasting forty-five to sixty minutes. Their program included depth jumps, box jumps, horizontal bounds, reactive jumps, and medicine ball throws, with training volume ranging from eighty to one hundred twenty foot contacts per session. Intensity progressed from bilateral movements to unilateral exercises while drop heights and reactive components increased, all designed to enhance the stretch-shortening cycle that underpins explosive athletic movement. Certified strength and conditioning specialists supervised every session, while the inspiratory training group’s home sessions from week three onward were monitored through adherence logs and weekly check-ins.

When the researchers measured lung function at baseline and again after twelve weeks, the differences between the groups were striking. The inspiratory training group improved forced expiratory volume in one second from 4.12 to 4.45 liters, an 8 percent gain, and forced vital capacity from 4.89 to 5.28 liters, also an 8 percent increase. Peak expiratory flow rose from 628 to 672 liters per minute. The plyometric group showed more modest but still significant improvements, with forced expiratory volume rising about 4.2 percent. The control group remained essentially unchanged across all measures. The most dramatic effect appeared in maximal inspiratory pressure, the direct measure of inspiratory muscle strength, which surged by 38 centimeters of water in the inspiratory training group, an effect size of 2.25 that the authors classified as very large, compared with only 12 centimeters of water in the plyometric group.

Importantly, the ratio of forced expiratory volume to forced vital capacity remained stable in all three groups. This preservation indicates that the improvements came from enhanced respiratory muscle strength rather than any change in airway caliber, a reassuring safety signal given concerns about exercise-induced bronchoconstriction in young athletes. Neither training modality induced pathological airway changes, and no serious adverse events were reported throughout the trial.

The most novel dimension of the study lay in its use of pupillometry. In a darkened room after five minutes of dark adaptation, each athlete received a standardized light stimulus to the right eye while a portable dynamic pupillometer recorded pupil diameter from both eyes at thirty hertz. The pupillary light reflex is governed by the autonomic nervous system: constriction velocity and maximum constriction percentage are associated with parasympathetic responsiveness, while re-dilation velocity has been linked to sympathetic function, though it is also influenced by parasympathetic withdrawal and measurement conditions. No previous study had examined how these reflex dynamics respond to inspiratory muscle or plyometric training in youth athletes.

The results revealed what the authors describe as distinct autonomic signatures. The inspiratory training group showed a 17.3 percent increase in constriction velocity, rising from 5.2 to 6.1 millimeters per second, along with a 10.5 percent increase in maximal constriction percentage. The plyometric group, meanwhile, displayed the largest improvement in re-dilation velocity, a 22.6 percent increase from 3.1 to 3.8 millimeters per second. The researchers propose that the inspiratory group’s faster constriction may reflect enhanced parasympathetic responsiveness, potentially arising from strengthened respiratory muscles reducing the work of breathing and its associated sympathetic activation, or from repetitive inspiratory resistance loading activating mechanoreceptors in the chest wall. The plyometric group’s faster re-dilation, conversely, may represent adaptive sympathetic responsiveness to the repeated high-intensity stretch-shortening cycles that demand rapid neural activation for force production.

Exploratory correlation analyses added another layer of intrigue. Changes in maximal inspiratory pressure were moderately associated with changes in pupillary constriction velocity across the pooled sample, and changes in forced expiratory volume correlated with changes in maximal constriction percentage. The authors caution that these correlations, computed on change scores across all three groups, may partly reflect between-group separation rather than pure within-participant physiological coupling, and they remain hypothesis-generating rather than proof of a mechanistic link between respiratory strength and autonomic regulation.

The authors are careful about the limits of their findings. Running performance was not assessed, so the results must be interpreted as physiological rather than performance evidence. The trial was not prospectively registered, participants and trainers could not be blinded, and the complete-case analysis excluded four withdrawn participants rather than imputing their data. Only forced expiratory volume was used in the sample-size calculation, making the remaining outcomes exploratory despite Bonferroni-corrected testing. Factors known to influence pupillary responses, such as sleep, screen exposure, and stress, were not systematically documented, and no formal pubertal maturation staging was performed across the fourteen-to-eighteen age range.

Nevertheless, the study represents the first randomized controlled trial to directly compare these two conditioning modalities on both pulmonary function and autonomic markers in youth middle-distance runners. The 8 percent gains in forced expiratory volume and vital capacity exceed the typical 2 to 3 percent year-over-year improvements attributable to natural adolescent growth, consistent with a genuine training effect. The authors suggest that a periodized approach combining both modalities might prove optimal: foundational inspiratory training during general preparation phases to build respiratory muscle strength, concurrent training during specific preparation, and maintenance-level inspiratory work during competition while emphasizing plyometric and speed work. Whether such combined programs deliver synergistic benefits, and whether the pupillary signatures observed here predict competitive performance or overtraining risk, remain questions for future trials. For now, the message for young runners and their coaches is clear: the muscles that power every breath respond to targeted training with remarkable specificity, and the eyes may reveal how the nervous system adapts alongside them.

Subject of Research: Comparative effects of inspiratory muscle training and plyometric training on pulmonary function and pupillary light reflex in youth middle-distance runners

Article Title: Effects of twelve-week inspiratory muscle vs. plyometric training on pulmonary function and pupillary light reflex in youth middle-distance runners—a three-arm randomized controlled trial

Article References: W., V., Tejaswi, J., Azeezul Kabeer, D., Karmakar, D., Kambitta Valappil, I. N., Parpa, K., Katanic, B., Geantă, V. A., Vveinhardt, J., & Govindasamy, K. (2026). Effects of twelve-week inspiratory muscle vs. plyometric training on pulmonary function and pupillary light reflex in youth middle-distance runners—a three-arm randomized controlled trial. Frontiers in Physiology, 17, Article 1781766. https://doi.org/10.3389/fphys.2026.1781766

Image Credits: AI Generated

DOI: 10.3389/fphys.2026.1781766

Keywords: inspiratory muscle training, plyometric training, pulmonary function, pupillary light reflex, autonomic nervous system, youth athletes, middle-distance running, spirometry, maximal inspiratory pressure, randomized controlled trial, exercise physiology, adolescent athletes