The aim of this investigation is to analyse the potential benefits of wearing a new commercially available microcurrent device combined with different exercise training modalities on exercise outcomes, body composition, recovery including muscle damage, general markers of health and immune function in athletes.

The investigation involves two randomised, balanced, double-blind parallel group between-participants design, aimed to analyse the effects of combining microcurrent with resistance and endurance training. Participants, once considered eligible for the study will be familiarised with the respective exercises, as well as tested for baseline values. Thereafter participants will be randomly assigned to one of the following intervention groups (1) Microcurrent (MCR+RT) with resistance training (2) Microcurrent (MCR+END) with endurance training (3) Sham with resistance training (SH+RT) and (4) Sham with endurance training (SH+END). Participants will perform 3 supervised training sessions per week (24 total workouts). Participants will wear the microcurrent or sham devices during 3 hr after workouts. Each group will follow a 10-week resistance or endurance training intervention combined with one of the two specific treatments (MCR or SH). Measurements of body composition, muscle thickness, performance, salivary and blood markers as well as delayed onset of muscle soreness will be determined before and after each particular (resistance or endurance training) intervention.

Participants It is anticipated that sixty participants, recruited from the Medway University Campus, will take part in the project. Inclusion criteria are: regularly trained male or female athletes, aged 18 to 45 years old, with at least 3 months of experience in resistance or endurance training, with no musculoskeletal injuries, metabolic conditions, or diseases or use of medications, smoking, and nutritional supplements known to affect physical performance, muscle damage or recovery processes (e.g., creatine, whey protein, and amino acids, vitamin or mineral supplementation, etc) within 6 weeks prior to the start of the study.

After being informed of all risks and potential benefits involved, participants will sign a written informed participation consent form. Procedures will be in accordance with the Helsinki Declaration and will be approved by the Research Ethics Committee of the University of Greenwich.

Intervention Resistance training groups

Familiarization period:

Participants will undertake 3 sessions of familiarization (1 week). To ensure a correct execution of the selected exercise a qualified strength and conditioning coach will control and assists participants. All participants will be instructed about the appropriate use of the Rate of Perceived Exertion OMNI-RES (0-10) scale to control the load and training intensity during each workout.

The resistance-training program is designed to increase strength and muscle mass of all major muscle groups. Under the supervision of strength and conditioning coaches, preferable a MSc Strength and Conditioning student from the University of Greenwich. The program will be undertaken on three non-consecutive days per week, Training workout will be performed during the afternoon (between 3 pm and 6 pm) with at least 48 hours between sessions.

The intervention period consists of a 8-week periodised resistance training programme divided into 3 blocks: First block (week 1 to week 3) using a moderate load intensity of around 70% 1RM; Second block (week 4 to week 6) where the intensity increases to >75% to 80% 1RM and the third block (week 7 to week 8) where the highest loads (>80 to 85% 1RM) are implemented. The Rate of Perceive Exertion OMNI-RES (0-10) scale (RPE) will be used to appropriately select the loading zone for each particular exercise during the workouts (Naclerio et al., 2015a, Naclerio et al., 2011)

Each workout session begins with individualized warm-up (5-minute warm-up stretches, followed by one set of eight repetitions of six resistance training exercises without any additional weight). Workouts will involve 3 sets of 8 to 10 RM (self maximal estimation) with approximately 2 min of rest of the following exercises:

1. Parallel back squat
2. Hang clean
3. Alternate lunges with dumbbells
4. Bench press
5. Upright row
6. Double leg dead lift
7. Push Press
8. Front shoulder press and
9. Biceps curl.

Each workout will last between 45 to 60 min.

The load will be increased or decrease based on the self-perception of the participants. When a minimum of 8 Reps is no possible to complete the participants will rest for 15sec and complete the set. Additionally, the participants can decide to reduce the load for the next set. Conversely, when more than 10 reps can be performed, the participants will stop the set, increase the load and complete the 10RM set.

Endurance training Participants will commit to follow a polarised triphasic endurance-training model. This model contains three intensity zones calculated as low intensity [≥ the first ventilatory threshold (VT1), ~ 70% HRmax]; moderate intensity [between VT1 and respiratory compensation point or ventilatory threshold 2 (VT2), >70 < 90% HRmax]; and high intensity [>VT2, 90% HRmax] (Esteve-Lanao et al., 2007). Participants will train 4 to 6 times per week with a total percentage distribution of 75 to 80% at low intensity; 10% at moderate intensity, and 15 to 10% at high intensity. Participants have to be completed the same time exposure to the MCR or SH device after the end of the intervention period.

Microcurrent or shadow

Both the microcurrent and sham devices will look exactly the same in terms of appearance, colour, size and weight. As the current transmitted from the microcurrent device is insufficient to stimulate sensory nerve fibres, this stimulus is imperceptible and together with the same appearance, participants nor strength and conditioning coaches or researchers involved in testing will be able to identify participants under the MCR or the SH treatment. Only one researcher not involved in the assessment and training supervision will know the participant allocation during the study.

Microcurrent or sham devices will be codified and placed on the participants before each training session. The participants will remove the device 10 to 15 min after completing each training session and return it to the strength and conditioning coach.

Inclusion Criteria:

• Regularly trained endurance or strength athletes
• Minimum of 6 months of experience

Exclusion Criteria:

• Musculoskeletal injuries, metabolic diseases
• Use of medications
• Smoking
• Consuming any nutritional supplements that potentially affect physical performance (e.g., creatine, whey protein, and amino acids) within 6 weeks prior to the start of the study

Double Blind (Subject, Investigator)