Relationship between (non)linear phase II pulmonary oxygen uptake kinetics with skeletal muscle oxygenation and age in 11–15 year olds

Abstract

New Findings Do the phase II parameters of pulmonary oxygen uptake (V̇normalO2) kinetics display linear, first‐order behaviour in association with alterations in skeletal muscle oxygenation during step cycling of different intensities or when exercise is initiated from an elevated work rate in youths. Both linear and non‐linear features of phase II V̇normalO2 kinetics may be determined by alterations in the dynamic balance between microvascular O2 delivery and utilization in 11–15 year olds. The recruitment of higher‐order (i.e. type II) muscle fibres during ‘work‐to‐work’ cycling might be responsible for modulating V̇normalO2 kinetics with chronological age. Abstract This study investigated in 19 male youths (mean age: 13.6 ± 1.1 years, range: 11.7–15.7 years) the relationship between pulmonary oxygen uptake (V̇normalO2) and muscle deoxygenation kinetics during moderate‐ and very heavy‐intensity ‘step’ cycling initiated from unloaded pedalling (i.e. U → M and U → VH) and moderate to very heavy‐intensity step cycling (i.e. M → VH). Pulmonary V̇normalO2 was measured breath‐by‐breath along with the tissue oxygenation index (TOI) of the vastus lateralis using near‐infrared spectroscopy. There were no significant differences in the phase II time constant (τtrueV̇O2normalp) between U → M and U → VH (23 ± 6 vs. 25 ± 7 s; P = 0.36); however, the τtrueV̇O2normalp was slower during M → VH (42 ± 16 s) compared to other conditions (P < 0.001). Quadriceps TOI decreased with a faster (P < 0.01) mean response time (MRT; i.e. time delay + τ) during U → VH (14 ± 2 s) compared to U → M (22 ± 4 s) and M → VH (20 ± 6 s). The difference (Δ) between the τtrueV̇O2normalp and MRT‐TOI was greater during U → VH compared to U → M (12 ± 7 vs. 2 ± 7 s, P < 0.001) and during M → VH (23 ± 15 s) compared to other conditions (P < 0.02), suggesting an increased proportional speeding of fractional O2 extraction. The slowing of the τtrueV̇O2normalp during M → VH relative to U → M and U → VH correlated positively with chronological age (r = 0.68 and 0.57, respectively, P < 0.01). In youths, ‘work‐to‐work’ transitions slowed microvascular O2 delivery‐to‐O2 utilization with alterations in phase II V̇normalO2 dynamics accentuated between the ages of 11 and 15 years.

Investigating the effect of sex, maturity, training status, and physical activity on performance and health-related parameters in children, adolescents, and adults

“…The results of Willcocks et al (2010) are supported by those of Breese et al (2019) who reported a decrease in the MRT of the tissue oxygenation index (TOI, %) during transitions to moderate and very-heavy cycling transitions in children and adolescents.…”

“…Recent advances in technology have allowed paediatric researchers to non-invasively examine muscle deoxygenation kinetics using near infrared spectroscopy (NIRS), typically examined at the m. vastus lateralis (Barstow, 2019;Breese, Saynor, Barker, Armstrong, & Williams, 2019;Marwood et al, 2010;Willcocks, Williams, Barker, Fulford, & Armstrong, 2010). The infrared light utilised is typically within the 700 -900 nanometre (nm) wavelength (Barstow, 2019), which allows the detection of lightabsorbing chromospheres, namely haemoglobin (HHb) and myoglobin (Mb; Barstow, 2019;Boone, Koppo, Barstow, & Bouckaert, 2009;La Mantia, Neidert, & Kluess, 2018;Ryan, Southern, Reynolds, & McCully, 2013).…”

“…The slowing of the [HHb] response with advancing age was attributed to a greater muscle mass in the older participants, facilitating a greater local O2 extraction, thus initiating a right-ward shift of the [HHb] response (Breese et al, 2019). However, the novel finding of Breese et al (2019) was that during the transition from moderate to very-heavy intensity exercise the slower pulmonary V ̇O2 kinetics were a result of a slower microvascular blood flow, not oxygen delivery (Breese et al, 2019).…”

“…The slowing of the [HHb] response with advancing age was attributed to a greater muscle mass in the older participants, facilitating a greater local O2 extraction, thus initiating a right-ward shift of the [HHb] response (Breese et al, 2019). However, the novel finding of Breese et al (2019) was that during the transition from moderate to very-heavy intensity exercise the slower pulmonary V ̇O2 kinetics were a result of a slower microvascular blood flow, not oxygen delivery (Breese et al, 2019). Endurance training augments this relationship, engendering a right-ward shift in both children (McNarry et al, 2011b) and young adults (Boone et al, 2009), which has been attributed to an increased abundance of type I muscle fibres and an increased SVmax and Q ̇max increasing oxygen delivery capacity (McNarry et al, 2014b;McNarry, Welsman, & Jones, 2011c).…”

“…One method of mV ̇O2 assessment, which has been increasingly utilised over the last decade in paediatric exercise science due to being non-invasive and relatively inexpensive in comparison to other techniques, is near infrared spectroscopy (NIRS; Barstow, 2019;Breese et al, 2019;McNarry et al, 2015). NIRS can estimate mV ̇O2 by utilising near infrared light in the 700-900 nanometre (nm) wavelength, calculated using the diffusion approximation of the transport theory of light, expressed as:…”