RESEARCH: Studies reviewed this week: 08 November 2021 to 14 November 2021

PHYSIOLOGY: Warm-up with a weighted vest improves running performance via leg stiffness and running economy

I've used a weighted vest for strength training while climbing and hiking and I'm familiar with the work on strength training and running economy, but I've never considered using a weighted vest during strides. This study set out to "determine the effects of "strides" with a weighted-vest during a warm-up on endurance performance and its potential neuromuscular and metabolic mediators". The protocol the study used was:

Each trial was preceded by a warm-up consisting of a 10-min self-paced jog, a 5-min submaximal run to determine running economy, and six 10-s strides with or without a weighted-vest (20% of body mass).

The results showed that:

The weighted-vest condition resulted in a very-large enhancement of peak running speed, a moderate increase in leg stiffness and a large improvement in running economy; there were also small-moderate clear reductions in cardiorespiratory measures.
Strides with a weighted-vest have a priming effect on leg stiffness and running economy.

PRACTICAL TAKEAWAY - strides with a weighted vest can improve running performance. However, this seems like a very risky protocol to start including in your warm-up so be cautious if you do decide to give it a try.

PHYSIOLOGY: Human skeletal muscle fiber type-specific responses to sprint interval and moderate-intensity continuous exercise

This study set out to understand the difference in response by muscle fibres to different training stimuli. The authors explained the protocol of the testing they used:

We examined mixed-muscle and fiber type-specific responses to a single session (study 1) and to 12 wk (study 2) of moderate-intensity continuous training (MICT) and sprint interval training (SIT) using Western blot analysis. MICT consisted of 45 min of cycling at ∼70% of maximal heart rate, and SIT involved 3 × 20-s “all-out” sprints interspersed with 2 min of recovery.

The results showed that:

Acute MICT and SIT elicited similar fiber type-specific responses of signaling proteins involved in mitochondrial biogenesis, whereas 12 wk of training revealed differential responses of mitochondrial content markers in type I but not type IIa fibers.
Only MICT increased [the] markers of mitochondrial content in type I fibers.

PRACTICAL TAKEAWAY - moderate-intensity continuous training is needed to increase mitochondrial biogensis in type 1 fibres while either moderate-intensity continuous training or sprint interval training can increase mitochondrial biogensis in type 2 fibres.

HEAT: Effects of Heat Acclimatization, Heat Acclimation, and Intermittent Exercise Heat Training on Time-Trial Performance

This study makes it clear exactly how to use heat acclimatization (HAz), heat acclimation (HA), and intermittent heat training (IHT). The test protocol involved:

A total of 26 male athletes completed five 4-km time trials in the heat (ambient temperature, 35.4°C ± 0.3°C; relative humidity, 46.7% ± 1.2%) on a motorized treadmill. After baseline time trial, participants performed HAz (109 ± 10 days) followed by post-HAz time trial. Then, participants completed 5 days of HA, which involved exercising to induce hyperthermia (38.50°C-39.75°C) for 60 minutes. Participants were then divided into 3 groups and completed IHT either twice per week (IHTMAX), once per week (IHTMIN), or not at all (IHTCON) over an 8-week period. Four-kilometer time trials were performed after 4 weeks (post-IHT4) and 8 weeks of IHT (post-IHT8).

The results showed that:

HA after HAz induces additional improvement in time-trial performance.
IHT twice per week shows improvement after 8 weeks, while once per week maintains performance for 8 weeks.
No IHT results in a loss of adaptations after 4 weeks and even greater losses after 8 weeks.

PRACTICAL TAKEAWAY - preparing for hot races can be challenging, but there are optimal strategies to do it and to maintain your adaptations through continued intermittent heat training.

EQUIPMENT: Increased footwear comfort is associated with improved running economy

I've shared two studies about shoe weight before (here and here) and both times my takeaways wer "prioritising comfort and appropriate cushioning over weight" and "when choosing race shoes choose the lightest appropriate shoe, but don't sacrifice significant comfort or cushion for weight". This review provides further proof about this type of decision.

The authors found:

The most comfortable footwear is associated with a reduction in oxygen consumption.
It can be concluded with moderate certainty that improved RE in recreational athletes is associated with wearing more comfortable footwear compared to less comfortable footwear.

PRACTICAL TAKEAWAY - choose comfortable shoes. My recommendation is always to choose the most comfortable shoe in the category that's appropriate for your competition. For example, for a short fast, road race, choose the most comfortable, lightweight racer.

HEAT: Exercise Heat Acclimation With Dehydration Does Not Affect Vascular and Cardiac Volumes or Systemic Hemodynamics During Endurance Exercise

This study sets out to answer the question of the impact of dehydration on adaptations during heat acclimation. This is an important practical study as it can definitely inform how we perform heat acclimation training. The protocol used in the study was that:

Seven males completed two 10-day exercise HA interventions with controlled heart rate (HR) where euhydration was maintained or permissive dehydration (-2.9 ± 0.5% body mass) occurred. Two experimental trials were conducted before and after each HA intervention where euhydration was maintained (-0.5 ± 0.4%) or dehydration was induced (-3.6 ± 0.6%) via prescribed fluid intakes.

The results showed that:

Neither HA intervention altered resting and euhydrated exercising Tre, BV, LV diastolic and systolic volumes, systemic hemodynamics, and VA coupling.
Furthermore, the thermal and cardiovascular strain during exercise with acute dehydration post-HA was not influenced by HA hydration strategy.

PRACTICAL TAKEAWAY - moderate dehydration does not impact the adaptations that come from heat training.

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