RESEARCH: Studies from 31 Mar to 6 Apr 25
Sharing research and insights from coaches, scientists and athletes to help us improve endurance performance.
This week’s quick summary:
No effect of carbohydrate-protein on cycling performance and indices of recovery
Effect of plyometrics on bone mineral density in young adults
Fluid retention, cardiac volume overload, and peripheral edema in ultra-cyclists
Red cell volume expansion at altitude
Vitamin C–enriched gelatin before activity augments collagen synthesis
NUTRITION: No effect of carbohydrate-protein on cycling performance and indices of recovery
Research has suggested that adding protein to carbohydrate (CHO) intake during exercise might enhance performance and recovery. However, evidence remains inconsistent. In this study, the authors aimed to “determine whether adding protein to a CHO beverage would improve late-exercise cycle time-trial performance over CHO alone”.
STUDY DETAILS
12 trained male cyclists took part in a double-blind, crossover study.
Cyclists completed 120 min of steady-state cycling at ~55% VO2 Max, followed by a 1-hour time trial while consuming either CHO alone (65g/h) or CHO + protein (65g/h CHO + 19g/h protein) every 15 min.
Performance and recovery markers were assessed over 24 hours.
Time-trial completion time, post-exercise isometric strength, plasma creatine kinase concentrations, and muscle soreness were recorded.
No significant differences were found between treatments in time-trial performance, strength loss (CHO: 15%, CHO + Pro: 11%), muscle soreness, or plasma creatine kinase levels.
PRACTICAL TAKEAWAY
The results of this study showed that adding protein to carbohydrate intake during cycling does not enhance late-exercise time-trial performance or improve recovery markers within 24 hours. My recommendation is that athletes do not need to include protein in their sports nutrition. Rather, focus on carbohydrates during training and achieving daily protein intake goals.
RELATED RESEARCH
STRENGTH: Effect of plyometrics on bone mineral density in young adults
Osteoporosis, a condition characterised by reduced bone mass and increased fracture risk, is a major concern as individuals age. Peak bone mineral density (BMD) is typically achieved in early adulthood, and maintaining it may help prevent osteoporosis later in life. In this review, the authors aimed to “analyse the effects of plyometrics on BMD in young men and pre-menopausal women”.
REVIEW DETAILS
The review analyzed randomized controlled trials (RCTs) published between 1990 and 2022.
Participants included healthy men and pre-menopausal women, ages 18 to 60.
The intervention involved plyometric training, compared to a control group or resistance-only training.
BMD was measured using dual-energy x-ray absorptiometry (DXA), assessing baseline and follow-up scores.
Results showed a significant increase in BMD at ≥1 site in 10 of 12 studies, with a large positive effect seen in lumbar spine BMD.
PRACTICAL TAKEAWAY
This review suggests that plyometric exercises, such as jumping training, are an effective and time-efficient method for increasing bone mineral density in young adults. Previous studies I have shared have also shown the benefit of plyometrics for improving running economy. My recommendation is for athletes to include some sort of plyometric training in their weekly scheduled. I suggest starting with a simple addition of skipping in warm-ups before hard sessions, then progressing to more complex plyometric exercises as strength develops.
RELATED RESEARCH
PHYSIOLOGY: Exercise-induced fluid retention, cardiac volume overload, and peripheral edema in ultra-distance cyclists
Ultracycling pushes athletes to extreme endurance limits, yet its impact on fluid balance and potential peripheral edema remains underexplored. In this study, the authors “investigated how multi-day ultracycling affects electrolyte regulation, fluid retention, and cardiovascular strain”.
STUDY DETAILS
13 ultracyclists (5 female, 8 male) participated in a 6-day ride covering 1205km and 19,417m of elevation. They underwent clinical assessments before, during, and after the event.
Body weight remained stable, but total body water increased by 1.98L, and plasma volume expanded by 18.86%, indicating significant fluid retention.
NT-proBNP levels rose by 297.99ng/L, reflecting cardiac volume overload. Facial and eyelid edema peaked on day 5 before partially resolving post-event.
Urinary sodium concentration declined until day 4, while plasma osmolality and copeptin increased, suggesting a shift toward fluid conservation.
Bioelectrical impedance and echocardiography confirmed extracellular fluid expansion, likely due to renal sodium and water retention.
PRACTICAL TAKEAWAY
These results show that ultra-distance cyclists may experience notable fluid retention and cardiac volume overload despite stable body weight. The authors suggest that monitoring sodium intake and fluid balance is crucial, especially beyond day 4, to mitigate edema and cardiovascular strain. My recommendation for athletes taking part in these events is to ensure that their hydration during the event includes enough sodium and is at a high enough level to support the activity. In theory this should help with their total water balance. Additionally, I recommend allowing sufficient rest after an event of this nature for adequate recovery.
RELATED RESEARCH
ALTITUDE: Red cell volume expansion at altitude
Altitude exposure is known to increase hematocrit, but the exact role and timing of red cell volume expansion remain unclear. In this meta-analysis, the authors aimed to “determine how much altitude exposure is required to induce polycythemia in healthy lowlanders”.
STUDY DETAILS
The extent of red cell volume expansion depends on altitude, with higher elevations leading to a faster response.
The initial red cell volume of an individual influences the erythropoietic response, affecting the degree of adaptation.
A minimum of two weeks at an altitude above 4000m is necessary to produce a statistically significant red cell volume increase.
At altitudes below 3000m, no measurable red cell volume increase occurs within four weeks of exposure.
The analysis included 66 studies with 447 volunteers, using a mixed-model random-effects meta-analysis and Monte Carlo simulation to assess responses.
PRACTICAL TAKEAWAY
This analysis suggests that athletes seeking red cell volume gains should train at altitudes above 4000m for at least two weeks. At lower altitudes, longer exposure is necessary, and altitudes below 3000m may not produce measurable effects even after four weeks. These are higher altitudes and longer durations than most athletes consider for altitude training camps. My recommendation is to take into account that improving red cell volume through altitude training is a demanding intervention. Athletes need to commit to long periods at altitude or go to higher altitudes than most popular altitude training locations to see improvement. Therefore, it may be worth considering if other interventions (such as heat training) may be more effective.
RELATED RESEARCH
SUPPLEMENT: Vitamin C–enriched gelatin supplementation before intermittent activity augments collagen synthesis
Musculoskeletal injuries remain the most common issue in active individuals, with over half involving damaged connective tissues like ligaments and tendons. Previous research suggests that nutritional strategies may enhance collagen production and reduce injury risk. In this study, the authors “explored whether vitamin C–enriched gelatin could stimulate collagen synthesis”.
STUDY DETAILS
8 healthy male participants completed a randomised, double-blind, crossover trial comparing 5g or 15g of vitamin C–enriched gelatin with a placebo.
Supplements were consumed three times daily for 3 days, with a 6-minute rope-skipping session 1 hour after each dose to stimulate collagen synthesis.
Blood samples were collected at multiple time points before and after exercise and supplementation to measure amino acid content and collagen synthesis markers.
Circulating levels of glycine, proline, hydroxyproline, and hydroxylysine peaked 1 hour post-supplement, with the 15g gelatin dose producing the highest concentrations.
Engineered ligaments treated with post-supplement serum showed higher collagen content and better mechanical properties; the 15g gelatin group had double the collagen synthesis marker levels compared to placebo.
PRACTICAL TAKEAWAY
In this study, taking 15g of vitamin C–enriched gelatin 1 hour before short bouts of exercise increased markers of collagen synthesis and improved ligament properties in lab models. My recommendation for athletes aiming to rehabilitate tendon or ligament injuries is to follow a strict protocol which uses gelatin supplementation with vitamin C and specific plyometric exercises that focus on their injury site. The dose used in this study was 15g of gelatin taken 1 hour before skipping for 6 minutes and this was repeated three times per day.
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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 (605 studies and practical takeaways). Last week, the newsletter covered studies on the following topics:
Different time course recovery of muscle after single- vs multi-joint exercises
Early time-restricted eating improves weight loss while preserving muscle
Pharmacological blockade of muscle afferents and perception of effort
Muscle protein synthesis with either 20g or 40g of ingested whey protein
Effects of an injected placebo on endurance running performance
