We are all still fully affected by the pandemic with various restrictions on our ability to circulate, meet people, exercise, socialise and perform our working duties. While this is painful for all us, we have to realise that such measures are absolutely important to reduce the spread of the virus and potentially save lives. By now we should all be familiar with the concept behind “flattening the curve” and we should be able to fully understand the relevance for our society to abide by the new rules introduced to safeguard public health.

Debates continue around the World, countries struggle to implement strategies and have to continuously adjust policies to make sure that the battered economies can survive while making sure public health remains a priority. Not an easy task for politicians and scientists involved in the decision making process, also when fake news, enthusiastic reports of preliminary trials, excessive optimism for some medical interventions and miraculous cures are continuously portrayed in the media. We all want this to end and return to normality, however reality is that it will take time and we need to be patient making sure scientists develop safe and effective solutions.

The World of sport has not been spared of course. For weeks, athletes have been dealing with cancellation of training activities, locking down of training venues, restrictions of access to coaches and support staff, cancellation of competitions. In recent days, some professional sports (in particular Football in Europe) have restarted training and competition activities and reports in the media seem to indicate a surge in injuries. I will attempt to discuss this providing some context, commentary and hopefully relevant information.

Before I make this attempt, it is important to state that there is no magic recipe and the only way to support athletes at this time is to safeguard their health, adopt individual approaches and carefully consider training interventions. What it is also important to state is that the press might overemphasise and over report injuries and illnesses putting a lot of pressure on sports science and sports medicine staff who are dealing with the unknown, just like any medical practitioner currently dealing with COVID-19. Thanks to rapid reporting, knowledge is growing every day and hopefully in few months time, we will be collectively better at supporting athletes and non-athletes in their return to sport. What we know today might change tomorrow and what we deal with today might be different from things we will deal with tomorrow. As a community, we should share knowledge and experiences and help each other in the quest to facilitate a safe return to sport not only for the professional athletes, but also for the general public keen and eager to return to ‘normality’.

What do we know about training during COVID-19?

While studies are ongoing with various international groups trying to collect evidence of the amount and type of training athletes have been performing during the lockdown/isolation/quarantine, we know just by looking at the social media and press reports that training activities have not stopped. Everyone has tried to help athletes continue their training with personalised or group training sessions performed at home.

Home training is not an easy thing to do as it depends a lot on the space available as well as the access to equipment. Also, in many countries, full lockdown measures were imposed (or are still imposed) which limit the possibility for athletes to exercise outside their homes and/or requires the use of masks or limitations in the distance from home allowed. Therefore, planning training for this situation requires creativity from the coaching staff and ways to engage the athletes individually or in groups to keep the motivation going and be able to sustain such training activities.

Football players have been sharing on social media their efforts.

Triathletes and swimmers had to improvise with personal pools, tethered swimming and dryland training as well as virtual competitions. Jan Frodeno also managed to complete a full Ironman at home!

Some track and field athletes managed to build a training facility in their back garden just like Greg Rutherford did before London 2012 and have been able to also compete. Watch the effort of the top Pole Vaulters in the World performing more than 30 jumps over the 5m height in their ultimate Garden Clash!

In general, all athletes have been incredibly resourceful in their ability to continue some form of training in order to retain their fitness to compete also reminding us why they are world class at what they do (the skills shown on this video are amazing, don’t try this at home unless you are as good as the athletes in the videos).

Many teams have also tried to continue group training sessions online using videoconferencing tools in order to also maintain the team ethos and attitudes while isolating.

As you can see from all the videos, the main characteristics of all these training sessions are:

• Limited space (most exercises are performed on the spot and/or with relatively limited movement)
• Use of some form of resistance (dumbbells, rubber bands, weights, weighted vests, bottles filled with water/sand etc.)
• Little and limited sports specific technical skills
• Absence of technical equipment for some sports (think about gymnastics/diving)
• Absence of contrast/opponents (think about how challenging is for combat sports but for any sports where interaction with the opposition occurs)
• No access to water for many in Aquatic sports (not all can afford or have access to a personal pool)
• Limited ability to perform technical skills at full speed (think about kicking a ball in football, throwing a ball in handball, throwing a javelin, repeating your floor routine in gymnastics, etc.)

So for every athlete, training has been highly challenging so far.

Cyclists are probably some of the few sports people who have been able to replicate most of their training activities thanks to the use of modern smart trainers and have been also able to compete online. However while this is possible, still the challenges of cycling in pelotons and/or on tracks and mountain bike paths require completely different skills which cannot be replicated when your bike is fixed on a smart trainer.

For sure, any form of training at home is better than nothing since it has been the only way to try to retain or improve fitness during isolation. So, whoever tried to design engaging training sessions for athletes in this situation a big well done, since it is for sure not easy. To the athletes capable of being resourceful and creative also a big well done. We all know and recognise that being away for a long time from your equipment, teammates, coaching staff and training environments is not easy and everyone able to retain the focus and drive deserves recognition. For many athletes in fact this long period of absence from their training environment is the longest ever experienced and it is possibly similar to the absence due to big injuries, but I will write more on that later.

What it is also important to consider is the fact that while training activities have been performed at home once or twice per day (or more in some cases), it is likely that the rest of the time the athletes have been quite sedentary since in many countries they had to abide to the restrictions imposed on leaving their household. We know from various studies (albeit not on elite athletes) that just few days of sedentary lifestyle can be enough to induce muscle loss, neuromuscular junction damage and fibre denervation, alter insulin resistance, negatively influence aerobic capacity, and induce changes in body mass and body composition. If you want to read more about it, I suggest you read this review published few days ago by my Italian colleagues highlighting all the physiological changes induced by sedentarism. While we know that athletes are different and they were probably able to maintain some degree of high intensity activity, it is likely that the reduction in activity during the day and the alterations in nutritional practices might have influenced their body composition as well as some physiological functions which may be relevant for their ability to return to ‘normal‘ training and competitions routines.

The effectiveness of the training at home initiatives will depend on what the athletes were able to do in terms of the type and frequency of activity as well as the volumes and intensities. Therefore, it is difficult to provide generic advice on what to do on return to full training. One thing for sure is the approach to be taken might be similar to what is normally observed in pre-season when athletes are assessed on their fitness status and programmes are developed accordingly.

What do we know about periods of detraining and human performance?

There are quite a lot to studies published on detraining, however most have been conducted on non-elite athletes and/or with periods of detraining determined by the complete absence of training for up to 3-4 weeks. What we have been experiencing so far are periods of reduced training in most cases and/or adapted training combined with home isolation. While we discuss the possible physiological implications, one should never underestimate the psychological toll this has taken on athletes and therefore this aspect should be taken into account when supporting athletes at home and when they return to training. It is not my expertise nor the scope of this blog article, but if you want to read more about psychological aspects of isolation, you can read this review on adolescents mental health related to COVID, this work on the emotional impact on healthcare workers with COVID and this excellent paper on the 520days simulated mission to Mars.

Back to detraining now. When we look at the ability to generate Force and Power, there have been some indications that a period of detraining might produce remarkable reductions in well trained American Football and Rugby players. This systematic review suggested that studies indicate that trained athletes can retain the majority of their strength over short periods of detraining (i.e. 2–3 weeks). Other papers have also suggested that elite athletes may be able to retain maximum strength gains for up to 30 days (3–4 weeks) days after training has ceased (however most studies cited refer to middle-aged or older individuals and/or to shoulder strength measures).

To me, one of the most relevant papers I always look at when understanding strength training and detraining is this classical paper of Hakkinen and Komi (Hakkinen K, Komi PV. Electromyographic changes during strength training and detraining. Med Sci Sports Exerc 1983; 15: 455-60). In this study, they had 14 male subjects (20-30 yr) accustomed to weight training that went through progressive strength training of combined concentric and eccentric actions three times per week for 16 wks and then detrained. While this study was a complete detraining from maximal strength training, it provides a very relevant overview of what it may happen in athletes unable to perform strength training routines they were used to. In this paper, the authors attributed the reduction in force generating capacity to the reduced neural drive evidenced in the EMG assessment.

More reviews on this and other aspects of training all indicate that periods of detraining (short or long) negatively affect muscle structure and function, the extent of which will depend on the duration of detraining, the individual athlete’s situation and characteristics and the extent of detraining (completed lack of training vs. other training activities). In the current situation, it may be possible that athletes are able to retain (if not improve) their strength and power abilities, provided they can experience appropriate training stimuli with enough volume and intensity to stimulate the neuromuscular system. However, this will need to be assessed when athletes are back to ‘normal’ training to identify the ones need of a re-introduction of strength and power training activities. While most studies refer to strength training exercises, it is important to consider that athletes training at home might have been able to perform strength training activities but not high speed movements requiring space (e.g. sprinting, jumping, throwing) at maximal or near maximal speed. In this case, little is known about the effects of detraining on sprinting, throwing speed, acceleration, etc. However the assumption is that if you don’t train such qualities you are likely to lose the ability to perform such tasks.

Detraining also affects the cardiovascular system. Recent work in semiprofessional soccer players has shown how remarkable the reduction in endurance capacity and repeated sprint ability is just after 2 weeks, but 2 weeks of retraining might bring it back to the previous levels.

A 2 weeks break characterised by detraining seems to be affecting more repeated sprint ability rather than endurance capacity in professional football players. We know that endurance capacity decreases with detraining but VO2 max might be maintained even with only one short 35-min high-intensity bout in well trained endurance athletes. Young well trained cyclists were shown to have marked reduction in various physiological parameters ((L · min⁻¹ = −8.8 ± 5.0%, mL · kg⁻¹·min⁻¹ = −10.8 ± 4.2%,), W_max (W = −6.5 ± 3.1%, W · kg⁻¹ = −8.5 ± 3.3%,), W_LT1 (W = −12.9 ± 7.0%, W · kg⁻¹ = −14.8 ± 7.4%,), W_LT2 (W = −11.5 ± 7.0%, W · kg⁻¹ = −13.4 ± 7.6%,) after 5 weeks of training cessation and an increase in body mass.

While we know quite a bit about detraining in general, we should be cautious in analysing the situation individually. In fact, many athletes have not been detraining at all and may be able to return fully fit (if not fitter) in most cases. For this reason, knowing what they have done and in what situation they are in when they resume activities would be a wise move.

Here we are making assumptions about athletes training from home and not affected by COVID-19 directly. In this case, there are a lot of other considerations to be taken into account.

What about the risk of injuries?

There have been already various reports in the press about injuries in Football due to the fact that this is the first sport returning to competitions. Various press outlets have reported injuries in Serie A teams returning to training, in Bundesliga teams during matches and training, in La Liga Teams in training. While there are not many details on the injuries, there seems to be reference to muscle strains in the calf, quadriceps, hamstrings. Such muscles are the ones at risk due to their involvement in sprinting, jumping, accelerating and decelerating.

At this stage it is impossible to ascertain if there is a higher incidence of injuries, there is no information on how the injuries occurred and why, there is no information if the athletes involved were directly affected by COVID-19 and therefore conclusions cannot be drawn. For sure there will be many press reports in the next few days and weeks but we will only know in the next months the true extent of this prolonged alteration in training habits on athletes. For now, we can only try to learn something every day.

The expectation is that the risk of injury increases with detraining, however this will depend a lot on the individual athlete, if he/she has been directly affected by COVID-19, the injury history, the sport they are involved in, the training they were able to do in isolation and the training and competitions they have to do when returning.

What we know is that a reduction in training has important consequences also on tendons. In particular, stiffness changes experienced in the Achilles’ tendons during detraining (if appropriate stimulation was not possible), might be related to changes in the structure of collagen fibers within the tendon. Therefore tendons and muscles in joints involving high speed movements are likely to require a gradual return to activity to reduce injury risks and the approach to be taken has to be very individual and adequate to the sport involved.

Is there any COVID-19 specific information out there?

As expected, there has been a large number of editorials, position stands and opinion papers published recently on sport and COVID-19. All are based on what we currently know and at the moment there is no experimental work published related to athletes (as of today). I am sure more will be published in the next few months.

For now, I suggest reading the following work:

Football Cannot Restart Soon During the COVID-19 Emergency! A Critical Perspective From the Italian Experience and a Call for Action

Return to Play After COVID-19: A Sport Cardiologist’s View

Coronavirus Disease 2019 (COVID-19): Considerations for the Competitive Athlete

Impact of potential physiological changes due to COVID-19 home confinement on athlete health protection in elite sports: a call for awareness in sports programming

Coronavirus disease (COVID-19): The need to maintain regular physical activity while taking precautions

Return to elite football after the COVID-19 lockdown

Position Stand: Return to Sport in the Current Coronavirus Pandemic (SARS-CoV-2 / COVID-19)

Finally, here you can find the Aspetar portal.

More information will be published for sure and we will be able to understand and know more about how to best serve athletes in the current situation.

Needless to say that while we focus on professional athletes, there is a bigger community of recreational athletes which requires support. For them, return to training and competition needs to be even more cautious to make sure the training activities are adequate and return to sport does not determine a prolonged reduction in physical activity due to injuries.

What about the athletes who have contracted the COVID-19 virus?

We know even less about this. Guidelines and advice are being produced as evidence is gathered and in line with the findings on the general population. The return for such athletes will depend a lot on the severity of the infection and their individual medical case.

The Lancet recently published some excellent work on respiratory health. Followed by a great blog and podcast here.

The American College of Cardiology has published a really useful article here highlighting how mechanisms of COVID-19 induced myocardial injury remain unclear but may be related to various aspects and require attention when reintroducing a patient to sport. Key papers on this aspect are the following two:

1. Baggish AL, Drezner JA, Kim JH, Martinez MW, Prutkin JM. The resurgence of sport in the wake of COVID-19: cardiac considerations in competitive athletes (Br J Sports Med Blog). 2020. Available at: https://blogs.bmj.com/bjsm/2020/04/24/the-resurgence-of-sport-in-the-wake-of-covid-19-cardiac-considerations-in-competitive-athletes/.
2. Phelan D, Kim JH, Chung EC. A game plan for the resumption of sport and exercise after coronavirus disease 2019 (COVID-19) infection. JAMA Cardiol 2020. [Epub ahead of print].

Few hours ago, the Professional Footballers’ Association in England has asked the Premier League to conduct extra research into the possible effect of Covid-19 on black, Asian and minority ethnic (BAME) players. This was triggered by data from the UK Office for National Statistics on COVID impact in the UK.

We will know more about the medical aspects of return to play once case reports will be published and more data will become available. At the moment, evidenced-based recommendations for return-to-play guidelines are currently limited and clearly subject to change as further data are obtained in parallel with improved COVID-19 case identification. Therefore, we need to be ready to change plans, adjust them when more knowledge becomes available and update the approach to the situations we face.

For sure a cautious approach is warranted and as a community we need to share information and develop safe and effective strategies.