PHYSIOLOGY: Changes in Running Kinematics, Kinetics, and Spring-Mass Behavior over a 24-h Run
Last week I shared a study about the biomechanics of marathon runners. This study "investigated the changes in running mechanics and spring-mass behavior over a 24-h treadmill run (24TR)". In these extremely thorough study, the authors measured multiple metrics:
Kinematics, kinetics, and spring-mass characteristics of the running step were assessed in 10 experienced ultralong-distance runners before, every 2 h, and after a 24TR using an instrumented treadmill dynamometer.
The findings were that:
Subjects' running pattern and spring-mass behavior significantly changed over the 24TR with a 4.9% higher step frequency on average (because of a significantly 4.5% shorter contact time), a lower maximal GRF (by 4.4% on average), a 13.0% lower leg length change during contact, and an increase in both leg and vertical stiffness (+9.9% and +8.6% on average, respectively).
During a 24TR, the changes in running mechanics and spring-mass behavior show a clear shift toward a higher oscillating frequency and stiffness, along with lower GRF and leg length change (hence a reduced overall eccentric load) during the support phase of running.
PRACTICAL TAKEAWAY - mechanics of running change over the course of long events. It's important to train for this shift and to be prepared for the running form that will appear later in races.
PHYSIOLOGY: Effect of General Warm-Up Plus Dynamic Stretching on Endurance Running Performance in Well-Trained Male Runners
My general advice about stretching is that static stretching before exercise is not good and that if you want to stretch then do some form of dynamic stretching. This study looked at warm-ups and dynamic stretching with the aim to compare "the acute effects of general warm-up (GWU) and GWU plus dynamic stretching (GWU + DS) on endurance running performance in well-trained male runners". The dynamic stretching group performed the following warm-up:
In the GWU + DS intervention, dynamic stretching was performed for ten repetitions as quickly as possible for the five muscle groups of the lower extremities. The total duration of the dynamic stretching was 3 min and 45 s. Endurance running performance was assessed at 1 min 15 s after the dynamic stretching.
The results showed that:
The time to exhaustion after GWU + DS intervention was significantly shorter than that after GWU intervention.
PRACTICAL TAKEAWAY - dynamic stretching may be detrimental to performance if included in a warm-up.
HEAT: The effects of pre- and per-cooling interventions used in isolation and combination on subsequent 15-minute time-trial cycling performance in the heat
I've shared multiple different studies on heat (see resources page) and preparation for this environmental condition. One of those previous studies suggested that cooling the neck may help reduce the impact of thermal stress. In this study the authors set out to investigate "the effects of pre- and per-cooling interventions on subsequent 15-min time-trial (TT) cycling performance in the heat".
The results are interesting as they show a perceptual benefit, but no increased performance:
Pre-cooling induced thermoregulatory benefits for ~45 min and perceptual benefits for the same duration when supplemented with per-cooling. Neck per-cooling offered no such benefits when used in isolation.
Neither pre- nor per-cooling, in isolation or combination, improved subsequent 15-min cycling time-trial performance in well-trained participants in the heat (40 °C).
PRACTICAL TAKEAWAY - cooling may provide some perceptual benefit, but doesn't appear to improve performance.
HYDRATION: Guidelines for Glycerol Use in Hyperhydration and Rehydration Associated with Exercise
I have heard about using glycerol to improve hydration prior to performance, but I've never investigated it thoroughly. This study starts out by explaining what the goal and mechanisms are:
Glycerol-containing beverages create an osmotic gradient in the circulation favouring fluid retention, thereby facilitating hyperhydration and protecting against dehydration. Many studies have shown that increases in body water by 1 L or more are achievable through glycerol hyperhydration.
The authors intended to investigate "the evidence for glycerol use in facilitating hyperhydration and rehydration, and provides guidelines for athletes wishing to use this compound". Their recommendations are:
- Endurance athletes intending to hyperhydrate with glycerol should ingest glycerol 1.2 g/kg BW in 26 mL/kg BW of fluid over a period of 60 minutes, 30 minutes prior to exercise.
- Ingesting glycerol 0.125 g/kg BW in a volume equal to 5 mL/kg BW during exercise will delay dehydration.
- Adding glycerol 1.0 g/kg BW to each 1.5 L of fluid consumed following exercise will accelerate the restoration of plasma volume.
PRACTICAL TAKEAWAY - using glycerol may benefit hydration status and performance in hot conditions.
LOAD: Relationships between Workload, Heart Rate Variability, and Performance in a Recreational Endurance Runner
This is a case study of a single recreational runner, but it provides some useful insights in various training load measurements. The authors recommend that:
The current results confirm the practicality of concurrent HRV and sRPE monitoring in recreational runners, with the RMSSD:RR ratio indicative of specific adaptations.
Excessive training volume may be associated to both elevated monotony and reduced RMSSD:RR.
Identification of mesocycle patterns is recommended for better individualization of the periodization used.
PRACTICAL TAKEAWAY - HRV and RPE can be effectively used together to help monitor training load.
CHO: Metabolic, hormonal and performance effects of isomaltulose ingestion before prolonged aerobic exercise
In this study the authors set out to test a low-GI carbohydrate. Their goals were to investigate "the effects of isomaltulose ingestion compared to glucose and maltodextrin on fat and carbohydrate oxidation rates, blood glucose levels and serum hormone concentrations of insulin and glucose-dependent insulinotropic polypeptide (GIP)".
The results showed that:
Isomaltulose ingestion led to lower baseline postprandial concentrations of glucose, insulin and GIP compared to maltodextrin and glucose.
Consequently, blood glucose fluctuations were lower during treadmill running after isomaltulose ingestion, while no between-condition differences were observed for CHO and fat oxidation rates, treadmill running performance and gastrointestinal discomfort.
PRACTICAL TAKEAWAY - the use of a lower-GI carbohydrate like isomaltulose may be beneficial for health while not impacting performance compared to glucose and maltodextrin.
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