RESEARCH: Studies from 9 to 15 Dec 24
Sharing research and insights from coaches, scientists and athletes to help us improve endurance performance.
This week’s quick summary:
The training intensity distribution of marathon runners
The metabolic response to 14 days of low energy availability
How strongly does appetite counter weight loss?
Variability in muscle fiber–type distribution affects running economy
The optimal weight carriage system for runners
TRAINING: The training intensity distribution of marathon runners across performance levels
Understanding training intensity distribution (TID) from a range of athletes is helpful for the purpose designing new training plans. In this study, the authors set out “to quantify the TID of marathon runners across a wide range of performance levels”.
STUDY DETAILS
The study analysed training sessions from 16 weeks preceding 151,813 marathons completed by 119,452 runners.
TID was quantified using a three-zone approach (Z1, Z2, and Z3), with critical speed defining the boundary between Z2 and Z3, and 82.3% of critical speed marking the transition between Z1 and Z2.
Average training volume across all runners was 45.1 ± 26.4km/week, with the fastest runners (120-150 min marathon time) accumulating over three times more volume than slower runners.
The proportion of Z1 training was higher in progressively faster groups, while Z2 and Z3 training remained relatively stable across performance levels.
A pyramidal TID approach was most common, adopted by over 80% of the fastest runners, with strong negative correlations between marathon time and training volume, and the proportion of training in Z1.
PRACTICAL TAKEAWAY
This study shows that marathon training is relatively simple. A pyramidal TID distribution with similar sessions in Z2 and Z3 by all levels of athletes appears to be effective. The fastest runners run significantly more and to achieve this they need to run in Z1. My recommendation for athletes training for the marathon is to plan some key race pace sessions (Z2 in this model), some key higher intensity threshold and VO2 Max intervals, and then to add as much easy training volume to each week as possible (depending on their own constraints whether those are physical, time-based, or motivational).
RELATED RESEARCH
NUTRITION: The whole-body and skeletal muscle metabolic response to 14 days of highly controlled low energy availability in endurance-trained females
Low-energy availability (LEA) can occur during periods when athletes are aiming to lose weight or during periods of extremely high training load. In general, it is advisable to avoid LEA as it can lead to performance losses and potential health consequences. In this study, the authors set out “to investigate the effects of 14 days of LEA versus optimal energy availability (OEA) on various physiological parameters and exercise performance in endurance-trained females”.
STUDY DETAILS
Twelve endurance-trained females (V̇O2 Max 55.2 ± 5.1 mL/min/ kg) participated in the study.
Participants completed two 14-day randomised, blind, cross-over, controlled dietary interventions: OEA (51.9 ± 2.0 kcal /kg FFM/day) and LEA (22.3 ± 1.5 kcal/kg FFM/day).
Exercise training volume was maintained during both interventions at approximately 8 hours per week at 79% heart rate max.
LEA resulted in a 7.8% impairment in 20-min time trial endurance performance, which persisted after 3 days of refuelling.
Fat utilization increased post-LEA, with higher resting plasma free fatty acids, larger reductions in FFA during exercise, and increased resting fat oxidation.
PRACTICAL TAKEAWAY
This study shows that endurance-trained female athletes should be cautious about maintaining low energy availability, as it can impair performance even after short-term refuelling. My recommendation, particularly for female athletes, is to avoid any periods of low-energy availability. This may require careful planning during training blocks and diligent daily protocols to ensure enough food is consumed before, during, and after training.
RELATED RESEARCH
Chronic carbohydrate restriction improves endurance capacity and body composition in men and women
Relationship between energy deficits and body composition in elite female gymnasts and runners
PHYSIOLOGY: How strongly does appetite counter weight loss? Quantification of the feedback control of human energy intake
One of the challenges of losing weight is that the body adapts to lower nutrition intakes by adapting the rate of energy used. In this study, the authors set out “to quantify how strongly appetite counters weight loss by examining energy intake changes during long-term covert manipulation of energy balance”.
STUDY DETAILS
153 patients participated in a 52-week placebo-controlled trial using canagliflozin, a sodium glucose co-transporter inhibitor.
Canagliflozin increased urinary glucose excretion, causing weight loss without patients being directly aware of the energy deficit.
A validated mathematical method calculated energy intake changes during the trial.
The relationship between body weight time course and calculated energy intake changes was analysed using engineering control theory principles.
Results showed weight loss led to a proportional increase in appetite, with patients eating approximately 100 kcal/day more per kilogram of lost weight.
PRACTICAL TAKEAWAY
This study showed that to counter weight loss, the body increased the participants’ appetite. The body naturally aims to stay in a state of homeostasis and this can be a challenge for athletes aiming to lose weight. My recommendation for athletes with weight loss goals is to measure their calorie intake and estimate the calories burned per day to try and achieve a small deficit. Using appetite and physical sensations is unlikely to result in effective weight loss.
RELATED RESEARCH
PHYSIOLOGY: Inter-individual variability in muscle fiber–type distribution affects running economy but not running gait at submaximal running speeds
Running economy is one of the critical components of endurance running performance. In this study, the authors set out “to resolve the ongoing debate by addressing potential confounding factors often overlooked in prior research, such as the effect of different running speeds, the homogeneity of investigated groups, and the potential impact of the adopted running gait”.
STUDY DETAILS
Participants were divided into two groups based on their triceps surae muscle fiber-type distribution: a predominantly slow-twitch group (ST; n=11) and a predominantly fast-twitch group (FT; n=10).
Muscle fiber-type distribution was determined by measuring carnosine levels using 1H-MRS, with the ST group having a carnosine z-score of -1.31 and the FT group having a z-score of 0.83.
Running economy was measured through indirect calorimetry across a range of speeds (2-4 m/s), along with running kinematics, kinetics, and muscle activity of the lower limb.
The ST group demonstrated, on average, 7.8% better running economy than the FT group, and this difference was consistent across all tested speeds.
Both groups showed nearly identical kinematics, kinetics, and muscle activity patterns across submaximal running speeds.
PRACTICAL TAKEAWAY
This study showed that runners with a higher proportion of slow-twitch muscle fibers in their calf muscles may have a natural advantage in running economy. While this characteristic is largely genetic, endurance training can potentially increase the proportion of slow-twitch fibers. My recommendation for athletes based on this study aligns with the recommendations from the TID study above: athletes aiming to perform in endurance running events should run as much easy training volume as they can cope with.
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EQUIPMENT: The optimal weight carriage system for runners: comparison between handheld water bottles, waist belts, and backpacks
Endurance runners often need to carry water and nutrition during long-distance events. Previous research has explored various carriage systems, but their comparative effects on running economy and physiological demands remained unclear. This study aimed "to compare the economy and physiological demands of different carriage systems".
STUDY DETAILS
Twelve recreational runners (average age 22.8 years, BMI 24.5 kg/m², VO2 Max 50.4 ml/kg/min) participated in the study.
Participants completed four 60-minute treadmill runs at individual speeds (average 9.5 km/h), carrying either no load or 1.0 kg in a handheld water bottle, waist belt, or backpack.
Running economy was assessed using energy cost (CR), oxygen cost (O2 cost), heart rate (HR), and rate of perceived exertion (RPE).
All measured variables (CR, O2 cost, HR, and RPE) increased over time during the runs.
No significant differences were found between the three carriage systems in terms of their effects on running economy or physiological demands.
PRACTICAL TAKEAWAY
Based on this study, runners can choose between handheld water bottles, waist belts, or backpacks for carrying 1.0 kg of water or nutrition during a one-hour run without concern for significant differences in running economy or physiological impact. My recommendation is for athletes to use the water carriage method they find most convenient and comfortable for them. My personal preference is not to use handheld bottles as I believe they have a cost of carriage with the weight further away from the core (although this is not shown in the study).
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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 (525 studies and practical takeaways). Last week, the newsletter covered studies on the following topics:
Which exercises target the gluteal muscles best?
Factors affecting sea-level performance following altitude training
Resistance training-induced changes in protein synthesis
The role of exogenous ketones in road cycling
Cold water immersion and percussive massage on recovery after exercise
