RESEARCH: Studies from 3 to 9 Feb 25
Sharing research and insights from coaches, scientists and athletes to help us improve endurance performance.
This week’s quick summary:
CHO restriction during recovery enhances fat oxidation in subsequent exercise and maintains performance when combined with caffeine
Explosive-strength training improves 5km time by enhancing running economy
Reduced training frequency maintains increased aerobic power
Caffeine intake improves running performance and time to exhaustion
Individually optimised footwear may reduce overuse injury risk
NUTRITION: Carbohydrate restriction during recovery from high-intensity-interval training enhances fat oxidation during subsequent exercise and does not compromise performance when combined with caffeine
In general, I recommend avoiding carbohydrate (CHO) restriction, as research shows that while restricting CHO can enhance fat oxidation, it may also impair performance. On the other hand, I always recommend caffeine, as it is well known to enhance endurance by altering substrate metabolism. In this study, the authors set out to "examine whether CHO restriction increases maximal fat oxidation (MFO) and whether caffeine mitigates performance losses."
STUDY DETAILS
17 trained female endurance athletes took part in a randomised, double-blind, placebo-controlled, crossover study.
Athletes followed three diet conditions: CHO restriction without caffeine (FASTED), CHO restriction with 300mg caffeine before exercise (FASTED+CAFF), and CHO ingestion after high-intensity interval training (HIT) (FED).
Each experimental block included evening HIT, followed by a fat oxidation test and a 20-minute time trial (20TT) the next morning.
MFO was assessed via a fat oxidation test, and cycling power output was recorded during the 20TT.
MFO was highest in FASTED+CAFF (0.57g/min) compared to FED (0.50g/min). 20TT power output was 6.9% higher in FASTED+CAFF than FASTED and 4.2% higher than FED.
PRACTICAL TAKEAWAY
The results of this study showed that female endurance athletes aiming to enhance fat oxidation may benefit from CHO restriction, while caffeine intake before exercise helps maintain power output despite low CHO availability. I remain cautious about recommending CHO restriction after training, as the potential costs may outweigh the benefits. However, for athletes incorporating some form of calorie restriction, I recommend using caffeine (3-6mg/kg bodyweight, taken ~60min before training) for all key sessions.
RELATED RESEARCH
STRENGTH: Explosive-strength training improves 5km running time by improving running economy and muscle power
One of the key factors in running performance is running economy, which is typically improved by increasing mileage and training at race pace. However, plyometric or explosive-strength training can also enhance running economy. In this study, the authors “investigated whether replacing a portion of endurance training with explosive-type strength training could enhance neuromuscular characteristics and improve 5km time without negatively impacting aerobic capacity”.
STUDY DETAILS
18 endurance athletes were divided into an experimental group (E, n=10) and a control group (C, n=8).
Over 9 weeks, 32% of E’s training was replaced with explosive-strength exercises, while C maintained traditional endurance training. Total training volume remained equal.
A 5km time trial, running economy (RE), maximal 20m sprint speed (V20m), a 5-jump test (5J), maximal anaerobic running test (MART), and VO2 Max were assessed.
E improved in 5km time, RE, V MART, V20m, and 5J. C showed no improvements in these measures.
VO2 Max increased in C but remained unchanged in E. 5km time improvement was correlated with RE and V MART gains.
PRACTICAL TAKEAWAY
The findings of this study showed that replacing some endurance training with explosive-strength exercises can improve 5km performance through better neuromuscular efficiency and running economy. This approach enhances speed and efficiency without increasing VO2 Max. My recommendation for athletes is to include two explosive-strength training sessions per week in their training plan. Exercises mentioned in the study include:
various sprints of 20–100 m
jumping exercises:
alternative jumps
bilateral countermovement jumps
drop and hurdle jumps
1-legged jumps
leg-press and knee extensor-flexor exercises
RELATED RESEARCH
TRAINING: Reduced training frequencies and maintenance of increased aerobic power
Endurance training and in particular high-intensity intervals can improve VO2 Max, but less is understood about the minimum frequency needed to maintain these gains. In this study, the authors aimed “to determine how often athletes must train to sustain their VO2 Max improvements”.
STUDY DETAILS
12 participants (average age 23) completed a 10-week endurance programme of cycling and running for 40 minutes per day, 6 days per week.
After 10 weeks, they were split into two groups, training either 4 or 2 days per week for 15 additional weeks, maintaining the same intensity and duration.
VO2 Max increased by 25% (cycling) and 20% (running) after the first 10 weeks.
Both groups maintained their VO2 Max over the following 15 weeks when tested every 5 weeks.
The findings suggest that VO2 Max can be preserved with just 2 or 4 high-intensity sessions per week.
PRACTICAL TAKEAWAY
The results of this study provide insight into the training required to maintain VO2 Max during periods of reduced training. Findings suggest that maintaining VO2 Max requires 33–66% of normal training volume. However, this likely depends on an athlete's training history and typical volume. While individual responses may vary, the study offers useful guidance for athletes facing temporary training limitations.
I recommend athletes reducing their training volume aim for at least 60–70% of their usual load while including 1–2 high-intensity sprint sessions per week.
RELATED RESEARCH
SUPPLEMENT: Effects of caffeine intake on endurance running performance and time to exhaustion
Caffeine is a well-established performance enhancer, particularly in aerobic sports. While its benefits for endurance exercise are well-documented, most research has focused on cycling rather than running. In this review, the authors aimed to "perform a systematic review and meta-analysis of the existing literature on the effects of caffeine intake on endurance running performance”.
REVIEW DETAILS
21 randomised controlled trials with 254 participants (220 men, 19 women, and 15 unspecified) were included. Participants were classified as 167 recreational and 87 trained runners.
The caffeine doses ranged from 3-9mg/kg, administered in crossover trials comparing caffeine to placebo under single- or double-blind conditions.
Running performance was measured using time-to-exhaustion tests and time trials. A meta-analysis assessed the results with a standardised mean difference calculation.
Caffeine significantly improved time to exhaustion in running trials, showing a medium effect size for both recreational and trained runners.
Caffeine reduced time to complete endurance time trials, but with a small effect size compared to placebo.
PRACTICAL TAKEAWAY
This review confirms that caffeine supplementation can enhance endurance running by increasing time to exhaustion and slightly improving time trial performance. My recommendation for athletes is to use caffeine before races and key training sessions. The optimal dose appears to be 3-6mg/kg bodyweight taken 60’ before running.
RELATED RESEARCH
Effects of moderate exercise on the pharmacokinetics of caffeine
Caffeine ingestion during exercise to exhaustion in elite distance runners
EQUIPMENT: Towards functionally individualised designed footwear recommendation for overuse injury prevention
Overuse injuries are a common concern in running, and footwear individualisation may help reduce this risk. In this scoping review, the authors set out to “examine footwear design features with the potential for individualisation to explore how different runner subgroups respond to these modifications”.
REVIEW DETAILS
107 studies on adult runners were included in the review, with a majority analysing male participants.
Studies assessed potential interactions between footwear features and runner subgroups (e.g., age, sex) for injury risk factors and biomechanical responses.
Footwear elements with individualisation potential include midsole properties, outsole profile, and upper construction, all of which influence biomechanics and comfort.
Female runners may be more sensitive to footwear-induced biomechanical changes and overuse injuries, highlighting the need for targeted research.
Despite promising trends, current research lacks comprehensive data collections on how specific footwear features systematically influence injury risk across diverse runners.
PRACTICAL TAKEAWAY
This review found that the evidence for shoe individualisation to prevent injuries was still limited and they recommended that further research is needed. However, they did note that certain features of the upper, midsole, and outsole could show potential for personalisation and reduction in injury risk. I think that there is a large range of different shoe brands and models that allow runners to experiment and find a shoe that works best for them. Therefore, my recommendation is to test different shoe models to find those that are most comfortable and fastest in field tests before trying to modify or individualise a pair of shoes.
RELATED RESEARCH
Does orthotics use improve comfort, speed and injury rate during running?
Running shoes for preventing lower limb running injuries in adults
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 (565 studies and practical takeaways). Last week, the newsletter covered studies on the following topics:
Low energy availability surrogates are associated with REDs outcomes
The intensity paradox and its impact on the fitness of older adults
Hydrolysed collagen supplementation for resistance exercise
Effects of caffeine on resistance exercise
Increased running speed and previous cramps predict cramping
