Recently, I came across a study that intrigued me by investigating the potential benefits of integrating sprints into extended endurance rides. This study challenges the conventional wisdom I've been following, which suggests maintaining controlled power levels during endurance rides, typically staying below the 'first ventilatory threshold' (VT1) or within the range of 55-75% of my Functional Threshold Power (FTP) or 60-70% of my Maximum Heart Rate (Max HR). The core idea behind this approach is that VT1 marks the intensity where optimal fat oxidation occurs. Going beyond VT1 tends to increase carbohydrate utilisation for energy, leading to higher lactate production and decreased fat oxidation.
This study, conducted by Bent Rønnestad and his team, aims to assess whether incorporating sprints into a lengthy endurance ride could potentially enhance the anticipated adaptations from such training.
Key Discoveries and Implications:
I decided to delve into this study, which involved 12 elite male cyclists, each training around 13 hours per week, with a VO2max of about 73.4 ± 4.0ml/kg/min. Participants were engaged in two separate 4-hour indoor rides. In one ride, participants maintained power at 50% VO2max (Zone 2 intensity) throughout the 4 hours. In the other ride, participants performed a series of 3x 30-second sprints with 4-minute recovery intervals each hour for the first 3 hours, while maintaining power around 50% VO2max between sprints. The researchers evaluated various markers in participants' muscles and blood at different time intervals after the ride.
The study's notable findings include:
Enhanced Aerobic Adaptations: The endurance + sprint session displayed higher levels of mRNA molecules associated with improved fat oxidation and the development of muscle capillaries. For instance, the endurance-only session showed a 2.8-fold increase in PDK4 (a molecule linked to fat oxidation) 20 minutes post-session. In contrast, the endurance + sprint session exhibited a remarkable 11.9-fold increase in PDK4 at the same point.
Managed Muscle Fatigue: Although the sprint training induced immediate muscle fatigue after the session, there were no noticeable signs of muscle fatigue after 24 hours.
Varied Effects on Mitochondrial Density: While the sprint session appeared to suppress a key mRNA molecule (PGC-1α) responsible for increasing mitochondrial density, the study's implications regarding this aspect remain nuanced.
Strengths, Limitations, and Implications:
As I analyse this study, I recognise its strengths, including meticulous control over variables like food and supplement intake, as well as the timing of the sprints. However, I'm aware of its limitations, such as the focus on markers instead of direct measurements of adaptations, and the study's exclusive focus on elite athletes.
Benefits of Integrating Sprints: This study suggests that incorporating sprints into endurance rides can potentially benefit well-trained cyclists, without causing excessive fatigue. This information could prove particularly valuable when your training involves predominantly low-intensity sessions or when you're seeking to intensify your training within time constraints.
Boosting Fat Oxidation: Contrary to my expectations, it seems that adding sprints doesn't necessarily reduce the stimulus for improved fat oxidation; instead, it could even enhance this training effect.
As I contemplate the implications of this study for my own training, I understand that the strategic arrangement of the sprint sessions within controlled intervals—alternating with well-controlled low-intensity riding—could be pivotal. This setup appears crucial to avoid prolonged elevation of lactate levels, which could potentially hinder fat oxidation.
In conclusion, if my goal is to enhance my fat oxidation ability, incorporating well-structured sprints within controlled endurance rides might yield positive outcomes. However, I'll be cautious about incorporating sporadic sprints without a thoughtful plan, as this may yield less effective results. This study provides valuable insights for refining my clients training strategies, especially as I consider leveraging INSCYD metabolic testing to tailor plans according to my clients individual goals and metabolic profile.
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