Each summary that I prepare adds to my archives and is distributed as a newsletter. If you're interested in either of those you can find them here:
- All the studies I've shared are available on the RESOURCES PAGE.
- The weekly summary is distrubted by email through my SUBSTACK NEWSLETTER.
This week's quick summary:
- Repeated-bout effect and lower-leg biomechanics
- The myth of exercise-induced immune suppression
- Response of human energy expenditure to physical activity
- Prior band-resisted squat jumps improve running performance
- Slow-paced breathing intervention improves sleep and performance
DOWNHILL: The repeated bout effect influences lower-extremity biomechanics during a 30-min downhill run
Downhill sections are crucial for performance in trail running ultramarathons so preparing for them in training is vital. Prior exposure and training using the repeated-bout effect can attenuate the negative impacts of descents. The authors of this study researched how this training impacts our running mechanics by determining “if the repeated bout effect influences changes in lower-extremity biomechanics over the course of a 30-min downhill run".
STUDY DETAILS
- Eleven male participants completed two bouts of 30-min downhill running (DR1 and DR2) at 2.8 m.s−1 and −11.3° on an instrumented treadmill.
- Maximum voluntary isometric contraction (MVIC) and perceived quadriceps pain were assessed before-after, and throughout the run, respectively.
- DR2 resulted in attenuated loss of MVIC, and perceived quadriceps pain compared to DR1.
- In general, participants ran with an increased duty factor towards the end of each running bout; however, increases in duty factor during DR2 (+5.4%) were less than during DR1.
- Significant reductions in leg stiffness and joint quasi-stiffness were observed during DR1 but not during DR2.
- The repeated bout effect significantly influenced lower-extremity biomechanics over the course of a downhill run.
PRACTICAL TAKEAWAY
A single session of downhill running helps to improve running biomechanics and future downhill running performance. This is good news for athletes who do not have regular access to mountainous terrain as they can plan a few 30' sessions before goal races and still see the benefit in the race. My recommendation is to do at least one 30' downhill session at race pace about three weeks out from the race. If an athlete has more access to steep terrain, then a downhill session every two to three weeks before a goal trail race will have significant benefit in the race.
PHYSIOLOGY: Debunking the myth of exercise-induced immune suppression
Training disruptions can have significant impact on performance which is why athletes should be as cautious as possible to avoid becoming sick leading up to events. One of the common perceptions of coaches and athletes is that "a vigorous bout of exercise can temporarily suppress immune function". In this paper, the authors "deconstruct the key pillars which lay the foundation to this theory—referred to as the “open window” hypothesis".
STUDY DETAILS
- Taken together, evidence that participation in an acute bout of vigorous exercise leads to heightened infection incidence remains spurious.
- In the context of mass participation sporting events, it is likely that increased exposure to pathogens, or the influence of environmental factors that can affect immune function (e.g., travel, sleep disruption) most likely explain genuine infections.
- Strong evidence implies that a reduction in the frequency and function of lymphocytes (and other immune cells) in peripheral blood in the hours following vigorous and prolonged exercise does not reflect immune suppression.
- Despite declines in fitness and immune competency, aging does not appear to negate the immunological benefits that can be attained from exercise, and indeed, frequent participation in exercise across the lifespan may lead to immune benefits, even in older age.
- We conclude that regular physical activity and frequent exercise are beneficial, or at the very least, are not detrimental to immunological health.
PRACTICAL TAKEAWAY
Vigorous exercise does not suppress the immune system. This is good news as it means that athletes do not have to avoid hard sessions around travel or leading into races based on a concern about immune suppression. However, it is important to note that even without immune suppression, there are certain situations that can pose a risk of both immune suppression and infection that should be avoided (travel, sleep disruptions, exposure to mass events).
PHYSIOLOGY: Is the response of human energy expenditure to increased physical activity additive or constrained?
Balancing energy expenditure and energy intake to ensure an energy balance is important to avoid periods of low energy availability. In male elite cyclists the correlation between daily intake and expenditure was only 0.6, and the variation between male and female athletes was significant. Understanding the response of energy expenditure to physical activity can help guide how athletes manage their nutrition.
STUDY DETAILS
- Human total energy expenditure (TEE) is the energy cost of all metabolic processes and is comprised of several components:
- sleeping metabolic rate (SMR);
- arousal (when awake); and
- cold- and heat-induced energy expenditure.
- The energy constrained hypothesis (constrained model) proposes that increased physical activity decreases other components of metabolism to constrain TEE.
- The evidence from empirical studies in humans often used to support the constrained energy expenditure hypothesis is underdeveloped, and more empirical data are needed with additional considerations of measurement and statistical approaches to confirm or refute this hypothesis.
- However, the evolutionary argument for energy expenditure compensation and constraint under conditions of increased TEE is persuasive.
- Energy expenditure should not be considered in isolation because there are important interactions between components of energy intake and energy balance which consequently affect energy expenditure.
- Based on current evidence, there is insufficient evidence to fully support either the additive or the constrained model of human energy expenditure.
- The available evidence indicates that in many scenarios, the effect of increasing physical activity on TEE will be mostly additive although some energy appears to “go missing” and is currently unaccounted for.
PRACTICAL TAKEAWAY
Measuring and accounting for energy expenditure is not simple. While increased physical activity does increase total energy expenditure, the relationship is not a direct increase and there is some "missing" expenditure. Practically, I would suggest that for athletes trying to control or lose weight, relying on calculations of energy expenditure to determine a calory deficit may not be accurate. The best metric to follow will be weight and then careful and iterative refinements in diet should be used to control it.
TRAINING: Prior band-resisted squat jumps improves running and neuromuscular performance in middle-distance runners
A previous study I shared showed that strides with a weight-vest can act as a priming effect that improves running economy. I think that this is a relatively risky priming activity so an alternative such as that investigated by this study is worth exploring. The authors set out "to characterize post-activation potentiation (PAP) conditioning stimulus effects on a subsequent 5x1 km running trial".
STUDY DETAILS
- A randomized, within subjects, repeated measures study utilized 12 male, endurance-trained athletes, who performed a full warm-up, conditioning exercise intervention (4x5 repetition maximum band-resisted squat jumps) or a control condition prior to a 5x1 km time trial run.
- Measures included the interpolated twitch technique (ITT), evoked contractile properties, maximum voluntary isometric contractions (MVIC) plantar flexor force, drop jump, rating of perceived exertion, and heart rate.
- The PAP stimulus reduced the time to complete the run, and decreased the time to complete kilometer one.
- F100 (force produced in the first 100ms of the MVIC) and MVIC force with PAP increased at kilometers 3, 4, and 7min post-run.
- Voluntary activation (ITT) increased at 7min post-run with PAP, yet decreased at 7min post-run in the control condition.
- A prior band-resisted squat protocol decreased running time and improved neuromuscular properties in endurance athletes running 5x1 km.
PRACTICAL TAKEAWAY
Post-activation potentiation appears to be a valuable warm-up activity to improve endurance performance. I would recommend trying the protocol from this study (4x5 reps of band-resisted squat jumps) before a training session and if it is effective to include it in a race warm-up.
BREATHING: A smartphone enabled slow-paced breathing intervention in dual career athletes
Breathing interventions can be effective for improving sleep and rhythmic breathing and inhalation strengthening can improve performance. This study set out to "discuss a four-week intervention delivered to dual career athletes which included screening stress and wellbeing, and a focus group discussion to capture athlete reflections on the slow-paced breathing (SPB) intervention".
STUDY DETAILS
- Eight dual career athletes (age = 20.75 ± 1.38, 3 female) competing at either national (4) or international (4) level (years of experience = 8.93 ± 3.32) agreed to take part.
- They were involved in a range of sports including wheelchair racing, athletics, basketball, golf and football.
- The intervention consisted of session 1: vmHRV and stress testing, session 2: SPB education workshop, four weeks of breathing training, session 3: vmHRV and stress testing (post), session 4: focus group.
- The athletes were instructed to practice breathing for 10 minutes a day, this was chosen given there was no dose response found for different durations of SPB regarding vmHRV during and immediately after SPB.
- Athletes clearly saw value in the intervention as reported in the focus group and observations of the data showed that for the majority of athletes wellbeing was improved and psychological distress reduced.
- Findings suggest SPB is successfully delivered via smartphones, positively influences stress management, sleep and performance, and may be a simple tool for practitioners and athletes to utilize.
PRACTICAL TAKEAWAY
Slow-paced breathing can be an effective means of managing stress, improving sleep, and positively influencing performance. In this study, the breathing practice was delivered by a smartphone application. My recommendation is to download an application and test a slow-paced breathing protocol. One option worth trying is HRV4Biofeedback (note, I work for HRV4Training).
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