The impact of low level laser treatment on skeletal muscle and skin tissue mitochondrial respiration, metabolic activity and signaling in vivo in humans

Low Level Laser Therapy (LLLT), also known as photobiomodulation, involves
utilizing light, often from a low-power laser or LED ranging between 5mW and
500mW, to target a pathological area, aiming to stimulate tissue regeneration,
alleviate inflammation, and provide pain relief. This technique has been
utilized for over four decades to treat musculoskeletal, tissue healing and
neurological issues. This light generally falls within the specific red or
near-infrared (NIR) spectrum (600nm - 1000nm), and it boasts a power density of
1mW to 5W/cm2. Treatment usually entails exposing the affected region to the
light for approximately a minute, repeated a few times weekly over several
weeks. It's important to note that unlike other medical laser interventions,
LLLT does not operate through ablation or thermal mechanisms; instead, it
relies on a photochemical process similar to photosynthesis in plants, where
light is absorbed and triggers a chemical transformation. Therefore, the laser
light is absorbed by the skin without causing heat damage, allowing it to
deeply penetrate tissues. Among the proposed effects are the stimulation of
mitochondrial respiration, enhancement of tissue oxygenation, and facilitation
of tissue regeneration.
Current body of research shows the greatest positive effects of LLLT when used
to treat cancer related oral mucositis and chronic pain. More recently LLLT has
been suggested to be a potential therapy for controlling blood glucose levels,
treat insulin resistance and support functional capacity outcomes in COPD
patients. All these (potential) positive effects have underlying mechanisms
that are not fully under stood.
LLLT has been shown to affect muscles after a single treatment. In rat models
LLLT can reduce muscle fatigue, decrease muscle damage and inhibit inflammation
processes. Similarly, LLLT showed increased muscle performance and improvements
of muscle metabolic state when combined with exercise in an acute setting in
humans. Interestingly, these acute effects have been proven when LLLT is
applied more long-term, over several weeks, with improvements in muscle
performance and damage. It has been suggested that the positive effects of LLLT
on muscle tissue are based on changes in energy metabolism due to a stimulation
of mitochondria, activation of muscle stem cells and favorable changes in
muscle remodeling gene expression. However, there is no in vivo data in human
on these underlying mechanism that can support muscle remodeling. Based on in
vitro research, suggested effects on muscle mitochondria might be the most
promising.
When muscle is stimulated by LLLT the skin undergoes LLLT at the same time.
Therefore the skin is simultaneously a target for positive remodeling
processes. It has been shown that LLLT can promote angiogenesis in the skin,
increase signaling of anti-inflammatory proteins, increase collagen synthesis,
support wound healing. Similarly to muscle, in vivo data to support these
suggestions and their underlying mechanisms in human are lacking.
To design better therapies using LLLT for a variety of conditions it is
important to understand the underlying mechanisms in a variety of tissues.
Within our research group collection of muscle and skin samples is considered a
standard procedure and both tissues are suggested to be affected by LLLT. Next
to that, in combination with our experience in the assessment of mitochondrial
respiration, gene expression, protein signaling and enzyme activity, we will be
able to study the underlying mechanisms of LLLT on tissue remodeling.

Primary objective: To assess the impact of acute laser treatment on muscle
tissue mitochondrial respiration in vivo in healthy, young adults.

Secondary objective: To assess the impact of acute laser treatment on muscle
cellular energy, anabolic, angiogenic and inflammatory pathways, along with
enzyme activity.

Tertiary objectives: To assess the impact of acute laser treatment on skin
cellular energy, anabolic, angiogenic and inflammatory pathways, along with
enzyme activity.

The present study utilizes an acute within-subject design in healthy young
adult participants. In total, 12 healthy young adults (6 men and 6 women) will
participate in the study. Participants* legs will be randomly assigned to low
level laser treatment or no treatment (Figure 1). Each participant will
participate in a screening session (~1 h) and 1 experimental test day (~1.5 h).

One leg of the subjects will receive LLLT, while the other leg will receive no
treatment. After the treatment muscle and skin biopsy samples will be taken
from both legs.

The risks involved in participating in this experiment are minimal. LLLT has
been shown to have no side effects and induce no harm. Muscle and skin biopsies
will be obtained under local anesthesia by an experienced physician. The muscle
biopsy may cause some minor discomfort, which is comparable to muscle soreness
or the pain one has after bumping into the corner of a table. Participants will
visit the University two times. The first visit will involve a screening visit
(1 h), during which the eligibility of the participant will be assessed and the
informed written consent will be obtained. For the second visit (experimental
trial, 1.5 h) participants are required to come to the University in a fasted
state, not having consumed any food or beverages (except for water) as from
22:00 the evening before. Also, 2 days prior to the experimental trial
participants need to record their food intake and activities performed. During
these 2 days participants are not allowed to perform heavy physical exercise or
drink alcohol. Filling out the food and activity log properly will take the
participant about 30 min each day. There is no direct benefit for the
participants, except from their contribution to scientific knowledge.