RESEARCH: Studies from 26 May to 1 June 25
Sharing research and insights from coaches, scientists and athletes to help us improve endurance performance.
This week’s quick summary:
Effect of 90’ and 120’ of running on the determinants of endurance performance
Sex differences in durability
Effects of hypoxic conditions on the gastric emptying rate
Inspiratory muscle training for middle-distance runners
Dietary carbohydrates influences short-term heat acclimation
PHYSIOLOGY: The effect of 90 and 120 min of running on the determinants of endurance performance in well-trained male marathon runners
Endurance performance in marathon running is influenced by VO2 Max, fractional utilisation at lactate threshold (FULT), and running economy (RE). These metrics are also closely related to the speed at lactate threshold (sLT). While these physiological variables are known to decline with fatigue, little is understood about their precise time-course deterioration during prolonged running. In this study, the authors aimed to clarify "how VO2 Max, FULT, RE, and sLT are affected after 90 and 120 minutes of continuous running in trained athletes".
STUDY DETAILS
14 well-trained male marathon runners (VO2 Max 63.1mL·kg⁻¹·min⁻¹; marathon time 2:46:58) completed three testing sessions: unfatigued, post-90min, and post-120min runs.
Each prolonged run was completed in the heavy-intensity domain (10% above lactate threshold 2), with respiratory gases collected every 15min to assess RE.
VO2 Max declined by 3.1% after 90min and 7.1% after 120min.
FULT increased by 2.8% after 90min and 4.9% after 120min, largely due to the reduction in VO2 Max.
RE worsened steadily (4.2% post-90min, 5.8% post-120min), and sLT dropped from 14.0 to 13.0km·h⁻¹ across the same time points.
PRACTICAL TAKEAWAY
This study showed that physiological determinants of endurance performance deteriorate meaningfully after 90min of heavy-intensity running, with more pronounced effects after 120min. My recommendation for runners is to consider these deteriorations in physical attributes and to account for them through key training sessions and good pacing during the marathon. One session that can help athletes become better at coping with marathon fatigue is 7km at marathon pace, 1’ easy, 3 x 3km at 10km pace with 1’ easy in between, and then 7km at marathon pace again.
RELATED RESEARCH
PHYSIOLOGY: Sex differences in durability: A field-based study in professional cyclists
Durability, the ability to sustain high performance over time and fatigue, has become recognised as a key performance determinant in endurance sports such as cycling. While durability has been assessed in male cyclists, little is known about how female cyclists compare. In this study, the authors aimed to “determine potential sex differences in durability”.
STUDY DETAILS
The study included 84 professional cyclists (42 female, 42 male) monitored over 1–5 seasons.
Power data from both training and competition were used to create record power profiles for 10s, 1min, 5min, and 20min efforts.
Power outputs were compared across different fatigue levels, defined as accumulated work of 0, 10, 20, and 30kJ/kg.
No meaningful decline in power output was observed below 10kJ/kg of accumulated work for either sex.
Female cyclists showed a greater relative decline in power output than males after 20kJ/kg and 30kJ/kg, particularly for 1min to 20min efforts, with differences increasing as fatigue accumulated.
PRACTICAL TAKEAWAY
This study showed that female professional cyclists experience greater declines in power output with increasing fatigue compared to male peers. It is not clear from this study why that might be - is it physiological or a result of different training? My recommendation for all athletes is to start by considering the demands of the race when planning training. For female athletes in long races, there may be some benefit to including more intensity in a fatigued state such as the marathon session in the practical takeaway above. Other alternatives may be including threshold or sprint intervals after accumulating 2-3 hours of work.
RELATED RESEARCH
ALTITUDE: Effects of endurance exercise under hypoxic conditions on the gastric emptying rate and intestinal cell damage
Previous research shows that endurance exercise can reduce gastric emptying and affect gastrointestinal function. Hypoxic conditions are known to increase cardiovascular and metabolic strain during exercise, but their effects on digestion remain unclear. In this study, the authors set out to “examine the effects of gastric emptying rate and intestinal cell damage following a single session of endurance exercise under hypoxic or normoxic conditions”.
STUDY DETAILS
11 healthy male participants completed two 60min treadmill runs at 70% vMax, once under normoxia (FiO₂ 20.9%) and once under hypoxia (FiO₂ 14.5%).
Running velocity was lower in hypoxia (10.8±0.5km/h) compared to normoxia (11.4±0.7km/h), despite matching relative intensity.
Gastric emptying was delayed in hypoxia, with peak ¹³C excretion time increasing from 38.5±5.0min in normoxia to 45.5±9.6min in hypoxia.
Ratings of nausea increased only after exercise in hypoxia.
No significant differences were found between conditions for plasma I-FABP, adrenaline, or noradrenaline levels, suggesting no added intestinal cell damage under hypoxia.
PRACTICAL TAKEAWAY
This study showed that endurance running under hypoxic conditions slows gastric emptying and increases post-exercise nausea compared to the same relative intensity under normoxia. My recommendation for athletes is to perform a period of acclimation before a race at altitude. Then, based on how they have adapted (and for athletes who don’t have the chance to go to altitude), to adjust their race nutrition plans and pacing plans to account for the altitude. Most likely, these adjustments will be lowering the intended pace and reducing nutrition intake to match the lowered intensity.
RELATED RESEARCH
PHYSIOLOGY: Inspiratory muscle training included in therapeutic and training regimens for middle-distance runners
Respiratory muscle training, particularly inspiratory muscle training (IMT), has been shown to improve ventilatory efficiency and endurance performance. However, the comparative efficacy of different IMT devices and their effects across genders in trained middle-distance runners remains unclear. In this study, the researchers aimed to “evaluate the effectiveness of respiratory muscle training in runners in relation to gender and trainers (PowerBreathe and Threshold)”.
STUDY DETAILS
32 high-level middle-distance runners (men and women) were randomly assigned to PowerBreathe IMT, Threshold IMT, or a sham control group.
Each group underwent IMT using either PowerBreathe or Threshold devices; the control group performed sham-IMT.
The intervention lasted several weeks, though the exact length was not specified.
VO₂/kg, peak expiratory flow (PEF), maximal inspiratory (PImax) and expiratory pressure (PEmax), lactic acid concentration, and lactate threshold were assessed.
PowerBreathe IMT significantly improved VO₂/kg, PEF, PImax, PEmax, reduced lactic acid levels, and increased lactate threshold in both sexes. Threshold IMT showed only a significant increase in PEmax, with no changes in other parameters.
PRACTICAL TAKEAWAY
This study showed that PowerBreathe IMT effectively improves ventilatory function, respiratory muscle strength, and endurance-related parameters in trained middle-distance runners. My recommendation for athletes is to use the PowerBreathe device for inspiratory muscle training. The devices are relatively cheap and the training is only a few minutes per day so the cost to potential benefit makes it an easy tool to recommend.
Alain Tremblay wrote to me to share his concerns about this study:
The authors did not even follow their methods which stated that ANOVA would (appropriately) be used to compare changes between groups. They only report changes from baseline to post training separately for each very small group of 5-6 people who were also starting a prep phase training block. No comparisons between the groups are provided at all (I suspect because the ANOVA was n.s. and therefore conveniently omitted…).
Intrasubject test-test variations in some of the parameters such as PEF and PI/PEmax can be very large even on the same day, and other physiologic measurements greatly affected by the phase of training the participants were in (they were not at a steady state). This study provides no evidence that these devices have any usefulness!
RELATED RESEARCH
HEAT: Dietary carbohydrates influence the performance outcomes of short-term heat acclimation
Heat acclimation (HA) improves physiological responses to heat, but short-term, exercise-intensive HA has been linked to impaired endurance performance immediately following acclimation. Nutritional strategies, particularly carbohydrate (CHO) intake, may influence these outcomes. Prior research shows that higher CHO availability supports performance in hot environments, yet few studies have evaluated this in the context of short-term HA. In this study, the authors aimed to “determine whether a high-carbohydrate (HC) diet can enhance 3.22km run time trial (TT) performance in the heat following exercise-intensive short-term HA”.
STUDY DETAILS
14 healthy military-age males were randomly assigned to either a high-carbohydrate (70% kcal from CHO) or moderate-carbohydrate (35% kcal from CHO) diet during and for one week following a 6-day HA protocol.
All participants completed daily exercise-intensive HA sessions and underwent testing for heart rate, core and skin temperatures, sweat rate, and TT performance in the heat.
Both groups showed physiological heat adaptation, with decreased heart rate, lower core and skin temperatures, and increased sweat rate after HA.
The high-CHO group improved 3.22km TT times significantly more than the comparison group both one and five days post-HA.
No differences were observed between groups in HA responses or relative effort during the TT, indicating the performance benefit was diet-related.
PRACTICAL TAKEAWAY
This study showed that consuming a high-carbohydrate diet during and after short-term heat acclimation improved endurance performance in the heat without altering heat adaptation markers. My recommendation for athletes performing heat training is to consider that the added stimulus of heat will have greater physiological demands. This means that it should be supported by greater carbohydrate intake to enable the right adaptations and benefits from performing under this stimulus.
RELATED RESEARCH
Quick summary from last week’s paid newsletter
Paid subscribers receive a newsletter every week and have full access to all newsletters listed in the archives (645 studies and practical takeaways). Last week, the newsletter covered studies on the following topics:
Ingestion of glucose or sucrose prevents liver but not muscle glycogen depletion
Sodium hyperhydration in female cyclists exercising in the heat
Long-term exercise capacity in SARS-CoV-2-positive elite athletes
Dose-response relationship between evening exercise and sleep
Boston Marathon performance outcomes associated with LEA indicators
