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Scanning Sports Medicine

Latest Clinical Research Published by ACSM

Kiningham, Robert B. MD, FACSM

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Current Sports Medicine Reports: April 2019 - Volume 18 - Issue 4 - p 93-94
doi: 10.1249/JSR.0000000000000587
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Grounded Running Reduces Musculoskeletal Loading

The health benefits of jogging are undeniable, but so is the injury risk, particularly among relatively deconditioned and overweight adults. Cumulative musculoskeletal load is thought to be a major contributor to running injuries, so an intervention that reduces the cumulative musculoskeletal load could decrease the risk of injury. This intriguing study published in the April 2019 issue of Medicine & Science in Sports & Exercise® (MSSE), altered the gait technique of runners at slow speeds to see if musculoskeletal loading could be reduced. Specifically, they studied the effect of eliminating the “flight phase” of running on muscle and skeletal loading, as well as impact intensity.

Traditionally, one of the four characteristics that distinguishes running from walking is the presence of a flight phase when both feet are off the ground. However, it has been observed that a significant number of “runners” at slow speeds actually engage in “grounded running” (GR), which is “running” without a flight phase. The other criteria for running are present in their gait: a vertical ground reaction force pattern showing a single maximum situated around midstance; a maximal bent knee around midstance; and in-phase fluctuations of kinetic and gravitational potential loading. Bonnaerens and colleagues (1) designed an experiment in which healthy young men underwent three conditions: slow aerial running (SAR) at 2.10 m·s−1, GR at 2.10 m·s−1, and aerial running at a population average running (PAR) speed of 3.20 m·s−1. Ground reaction forces (GRF), axial tibial acceleration (TA), vertical instantaneous loading rates (VILR), and oxygen consumption (V˙O2) were measured during each condition.

Thirty healthy males (average age, 23 years; body mass index [BMI], 22.9) were recruited. They were initially tested on their ability to perform GR, as determined by calculating stance time by stride time or duty factor (DF). A DF greater than 50% indicates the absence of a flight phase. Three subjects were unable to achieve a DF > 50% when instructed to engage in GR, and they were not included in the analysis. The three conditions were conducted in random order for 5 min each separated by a 3-min rest period. It was observed that subjects switched to GR from SAR by increasing stance time by 21.9% and decreasing swing time by 15.6% while keeping step frequency and step length the same (speed was 2.10 m·s−1 in both conditions). Analysis of GRF data revealed that muscle loading was about 20% lower for GR than SAR. Impact intensity, as measured by maximal TA and maximal VILR, was 31% to 35% lower in GR than SAR. As expected, the PAR condition had the highest loading and impact intensity. Energy expenditure for GR was actually 5% higher than for SAR.

This study had several interesting findings. The authors make the case that GR should be considered a running gait despite not having a flight phase. They demonstrated that with simple instructions, healthy young men can successfully perform GR at slow speeds. GR was found to significantly reduce muscle and skeletal loading and impact intensity at slow speeds compared to running slowly with a flight phase. Contrary to their hypothesis, energy expenditure for GR was slightly higher than for SAR at the same speed. This increased energy expenditure may have been due to the fact that the subjects were not habituated to GR, and thus were running with (for them) an unnatural gait.

This study has several limitations. The subjects were healthy, young active men, which is not the population in which GR is relevant. The authors chose to use active men so that they could conduct the “control” arm of the experiment, which was the PAR at 3.2 m·s−1. Now that this initial experiment has been done, it should be applied to more deconditioned, less active men and women to see if they can easily adapt GR, and if similar decreases in musculoskeletal loading and impact intensity occur. The truly clinically relevant study would then be a trial in which subjects are randomized to GR or traditional SAR to see if fewer running injuries occur in the GR group.

Bottom line: Grounded running (running without a flight phase) at slow speeds induces significantly less musculoskeletal loading and impact intensity than slow running with a flight phase. Future trials need to be done to see if GR results in fewer running injuries among runners who run at slow speeds.

Morning Versus Evening Aerobic Training Effects on Blood Pressure in Treated Hypertension

When patients ask me the best time to exercise, my usual answer is “whenever you will exercise.” My point is that exercise done regularly at any time is a lot better than exercise done sporadically at a specific time. However, this study out of Brazil challenges the assumption that the impact of exercise is the same regardless of the time of day it is performed.

This study, also published in the April 2019 issue of MSSE (2), compared the blood pressure (BP) lowering effect of aerobic training done in the morning to aerobic training done in the evening. The subjects were all men between the ages of 30 and 65 years who had been taking anti-hypertension medication for at least 4 months and were not currently exercising more than once a week. Exclusion criteria included secondary hypertension or target-organ damage, BMI ≥ 35, insulin use, presence of cardiovascular disease, taking beta-blockers or nondihydropyridine calcium channel blockers (because of their effect on cardiac autonomic modulation assessment), or abnormal resting ECG. Subjects were randomly assigned to one of three groups: morning training (MT), evening training (ET), or a control group (C), half of which stretched in the morning and half stretched in the evening. Morning sessions were done from 7 a.m. to 9 a.m. and evening sessions were done from 6 p.m. to 8 p.m.

Two maximal cardiopulmonary bike ergometer exercise tests were done in the morning and in the evening on different days prior to starting the exercise training sessions. Subjects also underwent two resting cardiovascular evaluations, one in the morning and one in the evening of the same day. The primary outcome variable was clinic BP. Secondary outcomes included changes in ambulatory BP (averaged over 24 h), and cardiovascular autonomic modulation and cardiac sympathovagal tone calculated from HR and BP variability.

The training intervention for the MT and ET groups consisted of progressive aerobic training on cycle ergometer for 45 min for 10 wk. Training intensity was based on the results of the maximal cardiopulmonary exercise test done at the start of the study, and adjusted according to continuously monitored heart rates during the exercise sessions. The C group performed stretching exercises for 30 min.

Only the data for subjects attending at least 75% of the exercise sessions were included in the analysis, making this a non-intention-to-treat analysis. Fifty subjects completed the study, 15 in each of the MT and ET groups and 20 in C. Exercise intensity was closely monitored and similar for the experimental groups. Weight did not change in any group, while V˙O2max increased significantly and similarly in both MT and ET but did not change for C subjects. Therefore, the exercise stimulus appeared to be equal for the experimental groups.

After 10 wk of training, clinic systolic BP decreased significantly compared with C only for the ET group during the morning and evening cardiovascular assessments. These changes were accompanied by decreased systemic vascular resistance, decreased vasomotor sympathetic modulation, and increased baroreflex sensitivity. The average systolic BP decrease in the ET group was −5 ± 6 mm Hg during the morning assessment and −8 ± 7 mm Hg in the evening assessment. There was no change in the 24 h, waking, or asleep ambulatory systolic BP in any group. Diastolic BP did decrease significantly by −3 ± 5 mm Hg in the 24 h and −3 ± 4 mm Hg while asleep in the ET group but not in the MT group.

The strength of this study was the extensive efforts that were made to ensure that the two experimental groups were similar and that the exercise stimulus was the same. However, the study has limited generalizability. The study population was very specific. Whether or not ET is more beneficial than MT in other groups, for example, women or people not on antihypertensive medication, or on other health assessment variables besides BP is not known.

Bottom line: Aerobic training done in the evening is more effective than identical training in the morning in decreasing clinic systolic BP and 24 h and sleep ambulatory diastolic BP in men taking antihypertensive medication.

The author declares no conflict of interest and does not have any financial disclosures.


1. Bonnaerens S, Fiers P, Galle S, et al. Grounded running reduces musculoskeletal loading. Med. Sci. Sports Exerc. 2018; 51:708–15.
2. Brito L, Peçanha T, Fecchio R, et al. Morning vs evening aerobic training effects on blood pressure in treated hypertension. Med. Sci. Sports Exerc. 2018; 51:653–62.
Copyright © 2019 by the American College of Sports Medicine