A week ago, a new study published in Frontiers Physiology titled, “Effectiveness of Grounded Sleeping on Recovery After Intensive Eccentric Muscle Loading” investigated the effects of grounding on recovery in athletes.1
What the Heck Is Grounding?
For those who are unaware of what grounding is, the authors give a very brief explanation here in their introduction,
Grounding, earthing, or grounded sleeping, is a process in which the athlete becomes grounded via an electrically conducted device. The person is grounded in an indirect way that corresponds to being barefoot with direct, continuous contact with the earth. Nowadays, it is almost impossible to be earthed, due to urbanization, insulating footwear or bituminization. There are various grounding systems available that permit contact with the surface of the Earth.
This indirect way of earthing or grounding is based on trivial conductive systems like sheets, mats, wrist or ankle bands, adhesive patches that can be used during sleeping or working, or inside footwear. These devices get coupled to the Earth by a typical cord slotted into a grounded wall outlet (Oschman et al., 2015).
Referring to Chevalier et al. (2006); Oschman (2007), and Oschman et al. (2015) the main hypothesis about earthing is based on the connection to the surface of the Earth, which is satiated with free electrons. This indirect or direct contact with the Earth enables “mobile” electrons to migrate into the body. Oschman (2007) suggests that these free electrons act as antioxidants in the organism and could neutralize reactive oxygen species (ROS).
ROS are byproducts of mitochondrial metabolism of oxygen and delivered by the oxidative burst as part of the inflammation response. Harman (1956, 2009) postulated that these reactive chemical species are linked to the aging process, originally known as free-radical theory of aging, and in the 1970s was extended to the mitochondrial theory of aging.
Over the past several years, an emerging body of evidence is starting to indicate that ROS are associated with tumorigenesis, cancer and chronic inflammatory systemic diseases (Reddy and Clark, 2004; Waris and Ahsan, 2006; Gupta et al., 2012). Consequently, Oschman (2007) suggests that the earthing based mobile electrons could also prevent or diminish inflammation.
So the basic hypothesis behind grounding is that the Earth contains free electrons, and these free electrons can reach the body when it is in direct contact with the ground and the electrons act as antioxidants to neutralize certain compounds known as reactive oxygen species, which in excess, can damage the cells within the body and promote inflammation, and a whole host of other problems.
The Problem with Free Radicals and Antioxidants
It’s a very appealing hypothesis. One that has had a significant influence on nutrition research and has led to several studies on the effects of antioxidants found in both foods and supplements. For example, nearly a decade ago, several databases contained the Oxygen Radical Absorbance Capacity (ORAC) of foods due to the sudden interest in antioxidants and their ability to neutralize free radicals within the body.
However, as more conflicting evidence emerged, several government agencies removed such databases due to the lack of evidence that the ORAC content of a food had any impact on clinical outcomes. Here’s what the USDA wrote about removing the database from their website,
“In 2012 USDA’s Nutrient Data Laboratory (NDL) removed the USDA ORAC Database for Selected Foods from the NDL website due to mounting evidence that the values indicating antioxidant capacity have no relevance to the effects of specific bioactive compounds, including polyphenols on human health.”
However, there are still many ORAC databases that exist, often hosted by non government websites and other organizations who believe that this information is useful. See this example from the Orac-Info-portal.de
This statement needs to be put in context. Antioxidants in both foods and supplements have been studied, however, much of the evidence has been of low quality and has not been robust for many health outcomes.
Here’s a summary of a few Cochrane systematic reviews and meta-analyses (which often tend to be more high quality, transparent, and thorough than other systematic reviews and meta-analyses):
AUTHORS’ CONCLUSIONS: There is moderate to low-quality evidence that high dose antioxidant supplementation does not result in a clinically relevant reduction of muscle soreness after exercise at up to 6 hours or at 24, 48, 72 and 96 hours after exercise.
There is no evidence available on subjective recovery and only limited evidence on the adverse effects of taking antioxidant supplements. The findings of, and messages from, this review provide an opportunity for researchers and other stakeholders to come together and consider what are the priorities, and underlying justifications, for future research in this area.2
AUTHORS’ CONCLUSIONS: Taking vitamin E or beta-carotene supplements will not prevent or delay the onset of AMD. The same probably applies to vitamin C and the multivitamin (Centrum Silver) investigated in the one trial reported to date. There is no evidence with respect to other antioxidant supplements, such as lutein and zeaxanthin.
Although generally regarded as safe, vitamin supplements may have harmful effects, and clear evidence of benefit is needed before they can be recommended. People with AMD should see the related Cochrane Review on antioxidant vitamin and mineral supplements for slowing the progression of AMD, written by the same review team.3
AUTHORS’ CONCLUSIONS: We found no evidence to support antioxidant supplements for primary or secondary prevention. Beta-carotene and vitamin E seem to increase mortality, and so may higher doses of vitamin A. Antioxidant supplements need to be considered as medicinal products and should undergo sufficient evaluation before marketing.4
Thus, much of the evidence from antioxidant supplements has been highly mixed over the years, often suggesting little to no benefit, or inconsistent effects. Many papers also discuss the concerns of high-doses of anxtioxidant supplements actually having a pro-oxidant effect. These concerns are supported by animal research that suggest that antioxidants may actually promote tumor growth in mice models of various cancers. However, it’s worth remembering these are animal studies and many phenomena seen in animal models don’t often translate to human trials.4–8
The Problem with Grounding
Anyway, back to this study on using grounding devices to deliver electrons from the Earth to the human body for recovery. Here’s what the authors write on the current state of evidence:
Actually, evidence-based research regarding the effectiveness of grounding is lacking. The narrative review of Chevalier et al. (2012) included grounding studies that indicated improvements in sleep (Ghaly and Teplitz, 2004), indices of DOMS (Brown et al., 2010; Brown et al., 2015), autonomic tone (Sinatra, 2011) and reduction in blood viscosity (Chevalier et al., 2013; Brown and Chevalier, 2015).
Due to the potentially reduced blood viscosity, enhanced blood flow velocity, improved sleep quality and decreased muscle damage, it is suggested that grounding could be implemented as a viable, effective recovery tool after strenuous exercise. However, currently, the evidence of treatment strategies to accelerate recovery after EIMD is still inconsistent (Connolly et al., 2003).
Therefore, the aim of this study was to investigate the effectiveness of grounded sleeping on the time course of DOMS and athletic performance after intensive downhill running. We hypothesized that grounded sleeping would alleviate exercise induced muscle and accelerate the recovery of athletic performance after strenuous downhill running.
It’s also worth noting that grounding has often been promoted by alternative health professionals. For example, here is alternative health guru, David “Avocado” Wolfe demonstrating the prowess of grounding in front of a live audience
It’s also worth nothing that this practice has been heavily critcized by skeptic groups and the scientific community.
“Dr. Mercola claims that a process called “grounding” or “earthing” can significantly change your health. Grounding or earthing refers to contact with the Earth’s surface electrons by walking barefoot outside or sitting, working or sleeping indoors connected to conductive systems, transfering the energy from the ground into the body.
Emerging research supports that this may result in reduced pain, better sleep and less inflammation. The logical explanation for the reduction in inflammation is that the Earth’s negatively charged antioxidant electrons enter the body and neutralize positively charged free radicals in the body. To get this benefit, Dr. Mercola recommends grounding or earthing sheets, made with fine thin strands of silver and which connect to an outlet; these cost about $200."
Regular readers of this blog should immediately recognize the above as being nonsense. Basically, it’s the overlaying of “science-y”-sounding terminology to earth worship, where the power of the earth somehow maintains and protects us, and the cause of all illness is because of man’s “disconnectedness” from the earth. Basically, it’s magical thinking on par with homeopathy. Yet it is the rationale for why Clint Ober recommends that everyone go barefoot and sleep on the ground.
Now that we have that background, we can dive back into the methods of this study. Some quick details:
"Twenty-two healthy sport science and physiotherapy students (mean ± SD; n = 22, 10 women, 12 men, age: 23.8 ± 3.2 years, weight: 67.2 ± 7.6 kg, height: 174.2 ± 6.3 cm) were recruited for this study…
A triple-blinded (participant, tester, and data analyst) randomized controlled design was used to evaluate the effects of 10 days recovery including grounded sleeping (GRD) or sham-grounded sleeping (UGD) after a single intensive downhill treadmill running intervention designed to induce DOMS…
All participants underwent a 20-min exercise bout of intensive downhill running (-25% slope, 12 km ⋅ h-1) on a motorized treadmill (Saturn 300/100 rs, h/p/cosmos sports & medical GmbH, Germany)…
During the 10-day post intervention, the GRD group slept grounded with a conductive sheet connected with a grounded wall outlet, while the UGD group slept sham-grounded. Both groups received identical sheets provided by BTZ (Badisches Therapie Zentrum, Baden-Baden, Germany) prior to the start of the study…"
The Problems with the Analyses
Okay, seems reasonable. Perhaps I could’ve missed some other interesting details in the materials and methods but what really caught my eye was this in the statistical analysis section,
“Alpha level of significance was set to 0.05. In addition, the values obtained were evaluated by calculating the effect size (η2p) and statistical power. The Statistical Package for the Social Sciences (Version 24.0; SPSS Inc., Chicago, IL, United States) was used for statistical analysis.”
No, I’m not horrified that they used SPSS, but this sentence about using obtained values for calculating effect size and statistical power made it seem like they were calculating observed power. I was doubting myself and thought, “Maybe I’m just jumping the gun, perhaps I should give the authors the benefit of the doubt.”
So then I head over to the results section…
"The time course of the absolute values in measured variables across the 10-days recovery period is presented in Table 3. With respect to the CMJ jump height there was a main effect of time (P < 0.001, η2p = 0.50, power = 1.0) and group, with a systematically lower reduction in GRD compared with UGD (-8.2 ± 5.4% vs. -14.3 ± 5.4%, P = 0.017, η2p = 0.25, power = 0.70) but no interaction in the time course of recovery between the two groups (P = 0.79). Lowest CMJ performance was achieved on the 1st day post intervention (Figure 2)…
For the DJ jump height, ground contact time and jump coefficient there was a main effect of time (all P < 0.001, η2p = 0.28 to 0.88, power = 1.0)…
For the MVIC in the dominant leg, a main effect of time (P < 0.001, η2p = 0.49, power = 1.0) and group (P < 0.03, η2p = 0.22, power = 0.61) with a less pronounced reduction in performance in GRD compared with UGD (-9.5 ± 16.8% vs. -17.3 ± 38.3%) was found. Day-to-day analysis revealed group × time interactions within the first 3 days with a more pronounced recovery in GRD compared with UGD (P < 0.05) (Figure 3). For the non-dominant leg, only a main effect of time was found (P < 0.001, η2p = 0.49, power = 1.0)…
With respect to CK levels main effects of time (P < 0.001, η2p = 0.30, power = 0.98) and group (P = 0.007, η2p = 0.31, power = 0.81) and an interaction effect time × group (P = 0.001, η2p = 0.26, power = 0.95)…
Regarding VAS only a significant effect of time (P < 0.001, η2p = 0.55, power = 1.0) with no main effect of group (P = 0.13) or interaction effect (P = 0.46) was found. VAS was highest at day 2…
So the authors are calculating observed power using the effect sizes they got from the study. I’ve written about this issue here and here. To reiterate, the problem with using the observed data to calculate statistical power is that it’s circular. Statistical power is a pre-design frequentist concept, “if I design this study with this many participants, in the long run, I’ll find a statistically significant effect this many times”. This is design power, which is based on beliefs of the population structure and effect size, which often tend to be overoptimistic.
The problem with using data from the study to calculate power is that it adds no new information and is not reflective of the actual power of the study. Let’s unpack this. A small study will likely yield noisy estimates with large standard errors, and trying to use such estimates to calculate the power of the study makes little sense.
If the study gives a statistically significant result, you’ll often get “high observed power” making you more confident in your results, if it’s not statistically significant, you’ll get “low observed power”, and in the latter case, you may be think “oh, our study didn’t have enough statistical power to detect an effect… blah blah blah.” Point is, single small studies do not provide enough useful information to draw any meaningful conclusions, but researchers often don’t think this way and rely on post-hoc observed power calculations to determine whether there study was useful or not.
Unforunately for them, observed power adds no new information and is simply a transformation of the observed P-value, which was discussed by Hoenig & Heisey nearly two decades ago.9 So what can we look at? The compatibility intervals.
All the effect sizes in the interval are reasonably compatible with the test model and its assumptions, while those outside of the interval are less so, but not completely incompatible. It’s far more useful to see what’s more compatible and what’s less compatible, rather than trying to improperly calculate the “power” of a study after we already have the data, which really isn’t even the actual statistical power of the study.
Also, note that the authors calculated 100% observed power for some of the outcomes. That means that they believe that if they used a similar design in the long run, they would always detect a statistically significant effect for a particular effect size of interest. Always. That should be an immediate red flag to anyone analyzing the data from such a study.
1. Müller E, Pröller P, Ferreira-Briza F, Aglas L, Stöggl T. Effectiveness of Grounded Sleeping on Recovery After Intensive Eccentric Muscle Loading. Frontiers in Physiology. 2019;10. doi:10.3389/fphys.2019.00035
2. Ranchordas MK, Rogerson D, Soltani H, Costello JT. Antioxidants for preventing and reducing muscle soreness after exercise. The Cochrane Database of Systematic Reviews. 2017;12:CD009789. doi:10.1002/14651858.CD009789.pub2
3. Evans JR, Lawrenson JG. Antioxidant vitamin and mineral supplements for preventing age-related macular degeneration. The Cochrane Database of Systematic Reviews. 2017;7:CD000253. doi:10.1002/14651858.CD000253.pub4
4. Bjelakovic G, Nikolova D, Gluud LL, Simonetti RG, Gluud C. Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases. The Cochrane Database of Systematic Reviews. 2012;(3):CD007176. doi:10.1002/14651858.CD007176.pub2
5. Assi M, Derbr’e F, Lefeuvre-Orfila L, R’ebillard A. Antioxidant supplementation accelerates cachexia development by promoting tumor growth in C26 tumor-bearing mice. Free Radical Biology & Medicine. 2016;91:204-214. doi:10.1016/j.freeradbiomed.2015.12.019
6. Hawk MA, McCallister C, Schafer ZT. Antioxidant Activity during Tumor Progression: A Necessity for the Survival of Cancer Cells? Cancers. 2016;8(10). doi:10.3390/cancers8100092
7. Sayin VI, Ibrahim MX, Larsson E, Nilsson JA, Lindahl P, Bergo MO. Antioxidants Accelerate Lung Cancer Progression in Mice. Science Translational Medicine. 2014;6(221):221ra15-221ra15. doi:10.1126/scitranslmed.3007653
8. Thyagarajan A, Sahu RP. Potential Contributions of Antioxidants to Cancer Therapy: Immunomodulation and Radiosensitization. Integrative Cancer Therapies. 2017;17(2):210-216. doi:10.1177/1534735416681639
9. Hoenig JM, Heisey DM. The Abuse of Power. Am Stat. 2001;55(1):19-24.