RESEARCH: Studies reviewed this week: 03 May 2021 to 10 May 2021

PHYSIOLOGY: Detection of the Anaerobic Threshold in Endurance Sports: Validation of a New Method Using Correlation Properties of Heart Rate Variability

This winter I used HRV Logger and the DFA1a metric to measure my aerobic threshold and to manage the intensity of my training (phase 1, phase 2 of my general preparation, HRV4Training blog on my base training). This recent paper from Bruce Rogers investigates the potential for using DFA1a to measure the anaerobic threshold.

The metrics in the study were used to make a:

Comparison of the HR reached at the second ventilatory threshold (VT2) was made to the HR reached at a DFA a1 value of 0.5 (HRVT2).

The results from this study showed that:

The HR associated with a DFA a1 value of 0.5 on an incremental treadmill ramp was closely related to that of the HR at the VT2 derived from gas exchange analysis.

PRACTICAL TAKEAWAY - DFA1a at 0.5 can be used as a proxy for determining VT2.

PHYSIOLOGY: The Importance of ‘Durability’ in the Physiological Profiling of Endurance Athletes

I have always wondered how useful laboratory tests are compared to field tests as the condition used in the lab are so different from those in training and racing. In addition to the different setting, there is the nature of the test. In this study the authors note that "attributes are typically assessed in well-rested athletes. However, as has been demonstrated in the literature and supported by field data presented here, the attributes measured during routine physiological-profiling assessments are not static, but change over time during prolonged exercise".

In this review the authors propose that:

Current models used in the routine physiological profiling of endurance athletes do not account for these shifts. Therefore, applied exercise physiologists working with endurance athletes would benefit from development of physiological-profiling models that account for shifts in physiological-profiling variables during prolonged exercise and quantify the ‘durability’ of individual athletes, here defined as the time of onset and magnitude of deterioration in physiological-profiling characteristics over time during prolonged exercise.

PRACTICAL TAKEAWAY - understanding athlete durability is important in testing and in understanding test results.

CHO: Effect of altered pre-exercise carbohydrate availability on selection and perception of effort during prolonged cycling

I've shared multiple papers on the impact of CHO on performance (see the resources tab). This paper is interesting as it tried to assess the "effect of altered carbohydrate (CHO) availability on self-selected work rate". The design of the study was as follows:

Eight endurance-trained men undertook two experimental cycling time-trials after glycogen-depleting exercise and 2 days of: (a) high (9.3 +/- 0 g CHO kg(-1) day(-1)) (HC) and (b) low CHO intakes (0.6 +/- 0.1 g CHO kg(-1) day(-1)) (LC), via a double-blinded crossover design. All feedback regarding performance was removed during both exercise trials.

The authors found that:

When compared with time-trial cycling performed after a HC diet, reduced CHO availability does not initially alter self-selected work rate in endurance athletes who are deceived of their CHO status prior to exercise.
This finding suggests that reduced work rate during exercise following lowered CHO intake may, in part, be a consequence of the subject's awareness of dietary CHO restriction rather than solely a physiologically mediated action.

PRACTICAL TAKEAWAY - awareness of diet and it's implications are important factors that could alter how athletes go about pacing.

CHO: Postexercise muscle glycogen synthesis with combined glucose and fructose ingestion

Glucose and fructose blends have been shown to be superior to pure glucose for CHO ingestion during exercise (see notes 1, notes 2, and notes 3). In this paper the authors tested to "evaluate the efficacy of using combined glucose and fructose (GF) ingestion as a means to stimulate short-term (4 h) postexercise muscle glycogen synthesis compared to glucose only (G)"

The results showed that:

Mean muscle glycogen synthesis rates during the 4-h recovery period did not differ between the two conditions.
Plasma glucose and serum insulin responses during the recovery period were similar in both conditions, although plasma lactate concentrations were significantly elevated during GF compared to G.

PRACTICAL TAKEAWAY - glucose/fructoses solutions were equally effective as glucose alone at restoring glycogen post-exercise. Therefore it's not necessary to use a special solution for recovery purposes.

FAT: Effects of a 14-day high-carbohydrate diet on exercise performance of a low-carbohydrate adapted athlete

This case study is a useful practical test to understand what happens to a LCHF athlete after consuming a high-CHO diet for 14 days. The conditions were that:

A trained male cyclist (VO 2peak =70 mL • kg-1 • min-1) following a LC diet (≤ 50g CHO • day-1) underwent a familiarization session to determine the baseline VO 2peak value and calculate the training intensities. Two testing sessions were performed following 14-days of LC and HC diet, respectively. The training loads were kept identical during both periods.

The results were:

Following the HC diet, time to exhaustion decreased in the moderate-intensity CP (+9%) but increased in the high-intensity CP (-3%).
These results suggest that introduction of a HC diet to a LC adapted athlete results in increased ability to perform high-intensity endurance performance while it decreases moderate intensity performance.

PRACTICAL TAKEAWAY - be carefully when changing diets as the impact may not be what is expected.

HYDRATION: Rehydration during Endurance Exercise: Challenges, Research, Options, Methods

This thorough review provides an excellent guide for hydration practices.

Some of my notes and highlights include:

  • Do not gain weight during endurance exercise.
  • Consume fluid at a rate less than 700 mL/h to reduce the risk of EHN.
  • If salt depletion is suspected (e.g., increased salt appetite or salt craving), it is prudent to consider adding specific dietary food items to ensure that daily sodium intake replaces exercise-induced sodium loss.
  • Athletes should be aware that sodium intake, while not discouraged, may provide little or no defense against EHN during prolonged exercise and the effects are unpredictable.
  • Experiment with rehydration options during training sessions, before using them in competition or in hot environments.

PRACTICAL TAKEAWAY - read this review!

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